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Abundance, Habitat Association, and Foraging Ecology of American Dippers and Other Riparian-associated Wildlife in the Oregon Coast Range

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by

John P. Loegering

A DISSERTAnON submitted to Oregon State University

in partial fulfillment of

the requirements for the degree of Doctor of Philosophy

Completed July 21, 1997 Commencement June 1998

•

AN ABSTRACT OF THE DISSERTATION OF

John P. Loegering for the degree of Doctor of Philosophy in Wildlife Science presented on July 21, 1997. Title: Abundance, Habitat Association, and Foraging Ecology of American Diwers and Other Riparian-associated Wildlife in the Oregon Coast Range. Abstract approved:

~J). ~J.--: ~

_

To quantify the distribution and abundance of the riparian-associated vertebrate community, I surveyed streams in four basins in the Oregon Coast Range, 1992-1994. I observed mostly birds with fewer observations of mammals. Belted Kingfishers (Ceryle

alcyon), American Dippers (Cinclus mexicanus), Great Blue Herons (Ardea herodias), and Mallards (Anus platyrhynchos) comprised >85% of these observations, but no one species was abundant Abundance of each species was affected by stream.order, basin, and season, but to varying degrees. Dippers and kingfishers selected channel unit habitats disproportionately to their availability. Key habitat components that were predictive of use were species specific. Riparian forests and streamside trees were important predictors of use by the three most abundant species; dippers, kingfishers, and herons. Second, I studied nest-site selection of dippers. Dippers selected nest sites based primarily on micro-habitat characteristics. Reproductive success was high and not associated with any habitat or parental foraging behavior. Suitable nest sites provided a physical space to place the nest, were above the upper flood line and inaccessible to ground predators, and were very near or extended over the stream's edge. Within the .context of mountain streams, dippers exhibited flexibility in their nest-site selection. Dippers used experimentally-creatednest sites, doubling the population on a 1o-kIn reach. Dipper populations appeared to be limited by the availability of suitable nest sites. Third, I studied foraging ecology of dippers by observing prey delivered to nestlings. Dippers fed nestlings a variety of invertebrate and vertebrate prey. Prey was mostly aquatic and composed primarily of mayflies, stoneflies, caddisflies, fish, and adult insects. Younger chicks were fed smaller prey and more mayflies than older chicks.

Older chicks were fed larger prey and more caddisflies and fish than younger chicks. Mayflies, stoneflies, and fish were fed more often to nestlings during the first than the second brood-rearing seasons. 'Jibe caloriccontent of prey delivered by males and females was similar. However, males delivered more, smaller prey items than females, and this was most pronounced when the females were broodingyoungchicks.

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©Copyright by John P. Loegering

July 21, 1997

All Rights Reserved


by

John P. Loegering

A DISSERTATION submitted to Oregon State University

in partial fulfillment of the requirements for the degree of Doctor of Philosophy

Completed July 21, 1997

CorrunencementJune 1998

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Doctor of Philosophy dissertation of John P. Loeeering presented on July 21. 1997

APPROVED:

Dean of Grad&£e School

I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request.

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ACKNOWLEDGMENTS First and foremost, I thank my major professor, Robert Anthony. I am grateful for

the superb support, guidance, and independence Bob gave me. Few students get the

opportunity to pursue their education with such freedom. I also am indebted to my

committee members Stan Gregory, John Hayes, ZoeAnn Holmes, Greg Linder, and Bill

McComb. Their comments, suggestions, and guidance greatly improved the focus of this

study as well as sharpened the fmal product. I acknowledge and appreciate the fmancial

support from the Coastal Oregon Productivity Enhancement (COPE) Program, directed

by Steve Hobbs, and the Bureau of Land Management. I also am grateful to the Oregon

Cooperative Wildlife Research Unit for fmancial and technical support throughout the

entire project.

I could not have completed this work without top-notch assistance in the field. It

was a privilege to work with a crew that responded so well to the challenges of chronic

rain, rugged topography, persistently leaky waders, long hours, and near-weekly

unexpected plunges into the stream. N. Verne Marr deserves the highest commendations.

He was an excellent field naturalist, keen observer, and diligent problem-solver. I also

am grateful for his patience, undauntable attitude, and sense of humor. I also thank Lisa

Loegering, Ken Popper, Amy Deller, Jennifer Purvine, and Julie Rosenthal for field

assistance. Bill Gerth was invaluable in helping me identify aquatic invertebrates.

I thank the many private landowners who allowed us access to their property. The

extent of our surveys could not have been completed without their permission. I am

grateful to Georgia-Pacific Corp., particularly Steve Delfs and Dick Paton, for assistance

and access and to the upper reaches of Drift Creek. I also thank the Siuslaw National

Forest and Bureau of Land Management for providing assistance and access to their

holdings.

My graduate experience would not have been complete without the support,

advice, assistance, and stimulation from fellow students, especially E. Pelren, C. Mam, J.

Snyder, and B. Steidl.

I cannot adequately thank my spouse and partner, Lisa. Lisa was involved with nearly every aspect of the project. She was patient, meticulous, and cheerful in the field. She keypunched the entire data set with admirable accuracy. She painstakingly read and improved various drafts of the dissertation. Finally, she supported me throughout the entire process. I am grateful. Finally, I thank Luke (age 4) and Isaac (2) for giving me a perspective I could not appreciate without them.

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TABLE OF CONTENTS

Chapter 1: General Introduction

1

Chapter 2: Distribution, Abundance, and Habitat Association of Riparian-associated Wildlife

3

INTRODUCTION

3

METHODS

5

Study Areas Stream Surveys Habitat Availability

5 7 10

STATISTICAL ANALYSES

11

RESULTS

13

"

Distribution and Abundance Streamside Habitat Features Channel Unit Use and Selection Stream Habitat Features DISCUSSION Distribution Abundance Streamside Habitat Association Channel Unit Selection Stream Habitat Association MANAGEMENT IMPLICATIONS Chapter 3. Nest-site Selection and Productivity of American Dippers

13 17 24 24 33 33 34 35 37 37 39 41

INTRODUCTION

41

METHODS

43

Study Area Nest Surveys .. , Artificial Nesting Structures

43 44 44

TABLE OF CONTENTS (Continued)


45

RESULTS

49

Habitat Selection Productivity Artificial Nest Sites DISCUSSION Habitat Selection Productivity Nest-site Dynamics Minimum Nest-site Requirements ~AGE~NTlMPllCATIONS

Chapter 4. Foraging Ecology of Breeding American Dippers

49

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70

INTRODUCTION

70

~THODS

73

Study Area Nest Observations Prey Preference Observation Biases STATISTICALANALYSIS Male - female Differences Early and Late Nesting Attempts Reproductive Success Prey Preference

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77

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80

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TABLE

on CONTENTS (Continued)

RESULTS Diets and Energy Composition Temporal Changes in Diet and Energy Delivered to Nestlings Prey Selection and Sexual Segregation during Brood Rearing Reproductive Success Censored Deliveries Prey Preference Bias DISCUSSION Diet and Temporal Variation in Diet Fed to Nestlings Prey Partitioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Male Parental Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prey Preference Reproductive Success SUMMARY

81

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85

90

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105

107

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Chapter 5: Summary

109

UTERATURE CITED

111

APPENDICES

125

LIST OF FIGURES

2.1

Oregon Coast Range study area map. .

3.1

Top view of a typical bridge crossing a mountain stream in the Oregon

Coast Range. .

48

The relationship between total number of American Dipper chicks fledged

/ nest site and stream shading from the overhead vegetation (A) and their

ranks (B) in the Oregon Coast Range, 1994

61

Abundance of active American Dipper nest sites along Drift and Lobster

creeks, Oregon Coast Range, 1993-1996

63

3.2

3.3

6

4.1

The number of mayflies (A), stoneflies (B), caddisflies (C), adult insects (D), fish (E), and total prey items (F) delivered / nestling / hour of observation to American Dipper nestlings in relation to chick age (n =91). . .. 83

4.2

The energy content (calories) of mayflies (A), stoneflies (B), caddisflies (C), adult insects (D), fish (E), and total prey items (F) delivered / nestling

/ hour of observation to American Dipper nestlings in relation to chick age

(n =91)

84

Cumulative frequency (%) of different-sized prey delivered to 5 age classes of American Dipper nestlings in the Oregon Coast Range. .

86

The number of mayflies (A), stoneflies (B), caddisflies (C), adult insects (D), fish (E), and total prey items (F) delivered / nestling / hour of

observation to American Dipper nestlings in relation to day number (n =

91)

88

The energy content (calories) of mayflies (A), stoneflies (B), caddisflies (C), adult insects (D), fish (E), and total prey items (F) delivered / nestling / hour of observation to American Dipper nestlings in relation to day

number (n =91). .

89

The difference (males - females) in the number of deliveries / nestling /

hour to American Dipper nests in relation to nestling ages in the Oregon

Coast Range (n = 77). .

93

4.3

4.4

4.5

4.6

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LIST OF FIGURES (Continued) Figure

4.7

4.8

4.9

Page

The difference (males - females) in the number of mayflies (A), stoneflies (B), caddisflies (C), adult insects (D), fish (E), and total prey items (F) delivered I nestling I hour to American Dipper nests in relation to nestling ages in the Oregon Coast :Range (n =77). .

94

The difference (males - females) in the energy (calories) contained in mayflies (A), stoneflies (I), caddisflies (C), adult insects (D), fish (E), and total prey items (F) delivered I nestling I hour to American Dipper nests in relation to nestling age in-the Oregon Coast Range

95

The difference (males - females) in the number of deliveries I hour to American Dipper nests where prey items were not seen (i.e., censored) in relation to nestling ages (A) and day numbers (B) in the Oregon Coast Range (n = 77). .

98

- - - - - - - ------

LISTOFTABLES

2.1

2.2

2.3

2.4

Habitat variables assessed at bird locations and randomly-selected points along Oregon Coast Range streams, 1992-1994. .

8

Physical characteristics of stream channel units identified during surveys of riparian-associated species in the Oregon Coast Range, 1992-1994 (from Bisson et al. 1982). .

9

Number of groups observed and mean group size of riparian-associated species in the Oregon Coast Range, 1992-1994

14

Abundance (individuals / 10 Ian of stream) of riparian-associated birds in 4-6th-order streams in the Oregon Coast Range, 1992. Values are least-squared means from the analysis of variance model including stream order, basin, and cycle effects (n = 53 surveys, 533 km of stream). .

15

2.5

Abundance (individuals / 10 km of stream) of riparian-associated birds in four basins in the Oregon Coast Range, 1992. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.6

Abundance (individuals / 10 km of stream) of riparian-associated birds during 1992-1994 in 4-5th order Drift and Lobster creeks, Oregon Coast Range. .

18

Streamside habitat characterizing sites used by and available to riparian-associated birds in the central Oregon Coast Range, 1992-94

19

Variables distinguishing between used and available streamside habitat for American Dippers, Belted Kingfishers, Great Blue Herons, and Mallards in the Oregon Coast Range, 1992-1994

20

Channel unit use by American Dippers (n = 95) and Belted Kingfishers (n =32) in Drift and Lobster creeks in the Oregon Coast Range, 1992-1994

25

Stream habitat characterizing sites used by and available to riparian-associated birds in the Oregon Coast Range, 1992. "

26

Variables distinguishing between used and available stream channel units for American Dippers, Belted Kingfishers, Great Blue Herons, and Mallards in the Oregon Coast Range, 1992. .

29

2.7

2.8

2.9

2.10

2.11

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LIST OF TABLES (Continued)

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

Micro- and macro-habitat variables considered in logistic regression models to discriminate between used and unused American Dipper nest sites for three nest types in the Oregon Coast Range, 1994

47

Total number of American Dipper nest sites (active and inactive), unused sites, and distance surveyed in 4-6th-order streams in the Oregon Coast Range, Cascades, and along the Oregon coast, 1994. .

50

Mean abundance (sites I linear 10 km of stream) of American Dipper nest sites (active and inactive) and unused nest sites in 4-6th-order streams in the Oregon Coast Range, Cascades, and along the Oregon coast, 1994. .

51

Proportion of American Dipper nests sheltered from the weather, accessible to avian and ground predators, and with a ledge present in the Oregon Coast Range, 1994. .

53

Micro- and macro-habitat characteristics at sites unoccupied and occupied by American Dipper nests on ledges, bridges, and in log cavities in the Oregon Coast Range, 1994

54

Streamside habitat at known American Dipper nest sites and randomly-selected locations in Drift and Lobster creeks in the Oregon Coast Range, 1992-94

57

Variables distinguishing between used and unused nest sites for American Dippers in the Oregon Coast Range, 1992-1994. .

58

Daily survival of American Dipper nests in Drift and Lobster creeks, among nest substrate types, at sites with natural and human-created substrates, and at natural and experimentally-created sites in Drift Creek in the Oregon Coast Range, 1993-1995. .

59

Daily survival of American Dipper broods prior to fledging in Drift and Lobster creeks, among nest substrate types, at sites with natural and human-created substrates, and at natural and experimentally-created sites in Drift Creek in the Oregon Coast Range, 1993-1995

60

LIST OF TABLES (Continued)

4.1

4.2

4.3

4.4

Macroinvertebrates and vertebrate prey used in preference trials for American Dippers in the Oregon Coast Range, 1993-94. .

76

Coefficients used to estimate weight and energy content of prey delivered to American Dipper nestlings in the Oregon Coast Range. .

79

Number of deliveries, number of prey items delivered, and estimated energy content of prey delivered to American Dipper nestlings in the Oregon Coast Range, 1993-1994, based on 2107 deliveries to nests in 270.7 hours of observation. .

82

Number and energy content (calories) I nestling I hour of prey delivered to nestlings during first and second broods (early and late seasons) by American Dippers in the Oregon Coast Range, 1993-94 (n 91 nest observation days). .

87

Number of nest deliveries, prey items delivered, and energy content (calories) delivered I nestlings I hour and % of observations where prey was not identified (censored) for chicks 0-10 days old, 11+ days old, and all ages combined by male and female American Dippers in the Oregon Coast Range, 1993-94

91

Number and energy content (calories) I nestling I hour of various prey delivered to nestlings by male and female American Dippers in the Oregon Coast Range, 1993-94

92

Mean rank of selection (e.g., 1 = selected first) and correlation of selection and caloric content for 11 different combinations of prey items offered to American Dippers from pans placed near nests in the Oregon Coast Range, 1994

99

=

4.5

4.6

4.7

4.8

Actual and observed lengths of prey delivered to nestlings by American Dippers during feeding trials in the Oregon Coast Range, 1993-94

101

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LIST OF APPENDICES Awendix

A

Streamside habitat characterizing sites used by and available to riparian-associated birds in the central Oregon Coast Range, 1992-94. On disk, filename APPNDX_A.TXT ........•......... . . . . . . . . . . . . . . . . .

...

126

B.

Stream habitat characterizing sites used by and available to riparian-associated birds in the Oregon Coast Range, 1992. On disk, filename APPNDX_B.TXT .•.•................•....•...•............ 127

C

Stream habitat characterizing sites used by and available to riparian-associated birds in the Oregon Coast Range, 1992. On disk, filename APPNDX_C.TXT

128

Streamside habitat at known American Dipper nest sites and randomly-selected locations in Drift and Lobster creeks in the Oregon Coast Range, 1992-94. On disk, filename APPNDX_D.TXT

129

Materials and dimensions.used to construct nest boxes for American Dippers in the Oregon Coast Range, 1993-1995. .

130

Mean abundance (sites / linear 10 km of stream) of American Dipper nest sites (active and inactive) and unused nest sites in 4-6th-order streams where dippers were found in the Oregon Coast Range, Cascades, and along the Oregon coast, 1994

131

Micro- and macro-habitat characteristics at sites unoccupied and occupied by American Dipper nests associated with roots and rootwads in the Oregon Coast Range, 1994 "

132

Micro- and macro-habitat characteristics at American Dippers nests on cliff ledges in the Oregon Coast Range and Cascades, 1994. .

133

Macro-habitat variables distinguishing between American Dipper nests on cliff ledges in the Oregon Coast Range and Cascades, 1994. .

134

Mean reproductive output per nesting attempt from American Dipper nest sites in Drift and Lobster creeks in the Oregon Coast Range, 1993-95 (n = 48 attempts)

135

Mean annual reproductive output from American Dipper nest sites in Drift and Lobster creeks in the Oregon Coast Range, 1993-95

135

D

E

F

G

H.1

H.2

1.1

1.2

LIST OF APPENDICES (Continued) Appendix

1.3

J

K.l

K.2

K.3

K.4

L

Total reproductive output from American Dipper nests in Drift and Lobster creeks in the Oregon Coast Range. 1993-95

136

Prey delivered to ligatured nestlings by American Dippers in the Oregon Coast Range. 1994.

137

The number of mayflies (A). stoneflies (B). caddisflies (C). adult insects (D). fish (E). and total prey items (F) delivered I nestling I hour of observation to American Dipper nestlings in relation to chick age (n = 91) (untransformed data)

138

The energy content (calories) of mayflies (A). stoneflies (B). caddisflies (C). adult insects (D). fish (E). and total prey items (F) delivered I nestling I hour of observation to American Dipper nestlings in relation to chick age (n =91)(untransfonned data)

139

The number of mayflies (A). stoneflies (B). caddisflies (C). adult insects (D). fish (E). and total prey items (F) delivered I nestling I hour of observation to American Dipper nestlings in relation to day number (n = 91)(untransfonned data)

140

The energy content (calories) of mayflies (A). stoneflies (B). caddisflies (C). adult insects (D). fish (E). and total prey items (F) delivered I nestling

I hour of observation to American Dipper nestlings in relation to day

number (untransformed data)

141

Number of nest deliveries. prey items delivered. and energy content (calories) delivered I nestling I hour and % of observations where prey was not identified (censored). by site. for male and female American Dippers in the Oregon Coast Range. 1993-94

142


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Chapter 1: General Introduction

The productive forest lands of the Pacific Northwest are transected by thousands of kilometers of streams, and the riparian areas associated with these streams have been increasingly scrutinized for their ecological value. Concerns for water quality and fish habitat initially spurred efforts to protect these areas from degradation. However, additional concerns for terrestrial vertebrates have led to modifications and expansion of the restrictions to activities and protection within the riparian zone (e.g., FEMAT 1993). Only recently have the needs of "lower" vertebrates, invertebrates, and plants been considered in the design and implementation of riparian zone management. Riparian areas are important to wildlife, and riparian-associated species represent a unique link between the aquatic and terrestrial components of the riparian zone. Riparian-obligate species are clearly dependent on both systems for their survival, but very little is known about the fundamental ecology of many riparian-obligate species, especially in montane systems. Therefore, my overall objectives were to identify riparian-obligate and -associated community, to quantify the distribution and abundance of these species, to identify important resources explaining these associations, and to further investigate the community's relationship with the stream systems.

In Chapter 2, I address the question of distribution, abundance, and habitat association of riparian-associated wildlife. Chapters 3 and 4 focus more closely on the American Dipper (Cinclus mexicanus), a resident, riparian-obligate species. Chapter 3 describes the nest sites, nest-site habitat selection, and reproductive success of dippers. Chapter 4 examines aspects of the foraging ecology of dippers; specifically, components of the diet fed to nestlings, prey preference, partitioning of prey resources by the male and

2 female, and parental care and investment. Finally, Chapter 5 summarizes the major findings of this work.


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3

Chapter 2: Distribution, Abundance, and Habitat Association of Riparian-associated Wildlife

INTRODUCTION The forest lands of western Oregon and Washington are some of the most productive in the world (Franklin and Dyrness 1973, Waring and Franklin 1979), and >78% of the approximately 35 million acres west of the crest of the Cascade Range is forested (Brown and Curtis 1985). These forests are dominated by conifers (Franklin and Dyrness 1973) and have been intensively managed for the production of wood products. Transecting these managed forests are many kilometers of stream. The interface between these streams and rivers and the upslope plant communities is known as the riparian area (Hall et al. 1985, Gregory et al. 1991). These areas are subject to conflicting land-use demands for development and timber harvest while increasing protection for water quality and fish and wildlife habitat.

Riparian areas are recognized as unique, highly productive, and diverse landscape

features (Agee 1988, Gregory et al. 1991); they are long, thin communities with a high

edge-to-area ratio. They are transition zones of hydrologic, topographic, and geologic

conditions and plant communities from upslope to valley floors. The year-round presence

of water promotes vegetative grdwth when the upslopes may be water-stressed and

periodic flooding creates a spatial mosaic of microhabitats. More dramatic disturbance

events, particularly debris flows and flood events, further structure riparian areas, often

creating high local diversity. They, along with their associated streams, provide a

network of interconnected landscape features from small, high-gradient headwaters to

lowland rivers. Riparian zones act as movement and dispersal corridors for plants and

animals throughout the watershed (Oakley et al. 1985, Gregory et al. 1991) or serve as a

population source to disturbed upland habitats. Riparian zones also serve as habitat to

aquatic invertebrates and vertebrates (Gregory et al. 1991) as well as terrestrial

vertebrates in their own right.

Subsequently published as:

Loegering, J. P., and R. G. Anthony. 1999.

Distribution, abundance, and habitat association of

riparian-obligate and -associated birds in the Oregon Coast Range. Northwest Science 73:168-185.

4 Riparian areas are important to wildlife (Bull 1978. Thomas et al. 1979. Oakleyet al. 1985), but little is known about the extent of the riparian-wildlife associations in the Pacific Northwest (McGarigal and McComb 1988). Timber harvest on private, state, and, to a lesser degree, federal lands previously proceeded without concern for riparian areas, and harvest units often have extended to the stream. However, guidelines to protect water quality and fish populations called for decreased harvest along streams and the retention of forested riparian areas. The benefits of these buffer strips to other wildlife species was largely unknown and of secondary concern. Further, information on the effects of management on wildlife species is required by the National Forest Management Act, National Environmental Policy Act, the Oregon Forest Practices Act, and the Threatened and Endangered Species Act. In western Oregon and Washington, 87% (n

=414) of the

resident species of amphibians, reptiles, birds, and mammals use riparian zones or wetlands (Oakley et al. 1985), and 10% are noted as using specialized habitats within riparian zones. In the Oregon Coast Range, most information is qualitative with some quantitative information on small mammals (Anthony et al. 1987Q. Com and Bury

1991~,

Suzuki 1992, McComb et al. 1993, Gomez and Anthony 1996), amphibians (Bury 1988, Com and Bury 1991Q, Gomez 1992, Vesely 1996), and songbirds (Carey 1988, Careyet al. 1991, McGarigal and McComb 1992). Even less is known about the vertebrates that are considered riparian obligates (Anthonyet al. 1987~, those that depend on riparian areas for foraging or habitat needs. Riparian species that could be sensitive to anthropogenic perturbation need to be identified. The purpose of this study was to assess the abundance, distribution, and habitat relationships of selected species in riparian areas of the Oregon Coast Range. I examined differences in abundance of species within and among basins, evaluated their habitat use and selection, and identified specific habitat features that distinguished between used and available habitat. I evaluated habitat associations at three spatial scales (Johnson 1980) of increasing specificity: large-scale habitat patches (Johnson's 2nd order; riparian zone and streamside features), specific habitat patches (3rd order; selection among stream channel units) and selection within each patch (4th order; discrimination within each channel unit). Specifically, I tested the hypotheses that: 1) the distribution and abundance of each

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5 species did not differ within and among basins, 2) species used habitat types in proportion to their availability, and 3) the stream and streamside habitat where I observed species was not different from available habitats.

METHODS Study Areas I surveyed Drift Creek (44° 25'N, 123° 80'W), Lobster Creek (44° 15'N, 123°

40'W),LakeCreek(44°7.5'N, 123° 35'W),andFiveRivers(44° 15'N, 123° 50'W)

basins in the central Oregon Coast Range (Fig. 2.1). These basins were in Benton, Lane,

and Lincoln counties and drained into the Alsea and Siuslaw rivers, 6-23 km east of the Pacific Ocean. The topography was steep with moderately flat valleys. Stream bed elevation ranged from 3 to 365 m. Average stream gradient was generally 0.05).

0.0292

0.0053

0.0816

VI

Table 2.5. Abundance (individuals /10 krn of stream) of riparian-associated birds in four basins in the Oregon Coast Range, 1992. Values are least-squared means from the analysis of variance model including stream order, basin, and cycle effects (n =53 surveys, 533 krn of stream).

Basin

American Dipper

Belted Kingfisher

-

-

x

SE

x

SE

Common Merganser

Great Blue Heron

Green Heron

x

SE

-

x

SE

-

x

SE

-

Mallard

Wood Duck

x

SE

x

SE

-

Drift Creek

5.7 Aa

0.7

5.3A

0.9

1.9A

0.7

1.2A

0.3

O.lA

0.2

1.7 A

1.4

0.8 A

0.4

Five Rivers

2.3 B

0.8

6.8A

0.9

l.OA

0.8

1.5A

0.3

O.lA

0.2

5.9 AB 1.5

0.8 A

0.5

Lake Creek

2.6 B

0.8

7.2A

0.9

0.9A

0.8

0.9A

0.3

0.6A

0.2

4.0 AB 1.5

0.9 A

0.5

Lobster Creek

1.2 B

1.0

6.2A

1.1

2.1A

1.0

2.0A

0.4

0.6A

0.2

8.5 B

0.8 A

0.6

0.0017 0.6593 0.4620 0.2141 P a column means with the same letters are not different (P > 0.05).

0.0779

0.0288

1.8

0.9957

-

0-.

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17 addition, I found no significant (P 5 0.05) first-order interactions among the effects of stream order, basin, and survey cycle for dippers, kingfishers, mergansers, Great Blue Herons, Green Herons, Mallards or Wood Ducks. There were no significant differences in abundance among years for any species (Table 2.6). Among the stream segments surveyed during all three years, only kingfisher and Great Blue Heron abundances were different among basin, stream order, survey cycle, and year (ANOVA, F = 4.0,23 df, P = 0.0134 and F = 3.08,23 df, P = 0.0352, respectively); however, these differences were not attributable to a year effect (P > 0.24). In addition, I detected no autocorrelation among the years for any species (Durbin-Watson D, all P > 0.10).

Streamside Habitat Features Each species was associated with different landscape and riparian zone features.

Four variables distinguished areas used by American Dippers from those that were

available (logistic regression,

'l =211, 14 df,

P = 0.0001, max. rescaled R2 = 0.2325). I

located dippers in areas where trees were the dominant riparian zone overstory species on

one (12.8% of the observations VS. 30.4% ofthe available habitat) or both stream banks

(82.0% vs. 59.3%, respectively, Table 2.7). Compared to streams with no riparian-zone

trees (logistic regression odds ratio = 1), I was less likely (90% confidence interval [CI]

on the odds ratio = 0.25 - 0.88, P

=0.047, Table 2.8) to fmd dippers where there were

overstory trees on one side of the stream but more likely to find dippers where both banks

had overstory trees. Dippers were 1.5 to 3.1 times (90% CI) more likely to be found on

reaches constrained by the valley walls on both sides of the stream (P = 0.0005, Table

2.8) than in unconstrained stream reaches, and this pattern was similar but not as pronounced for reaches that were constrained by only one valley wall (P = 0.27). I found dippers in constrained valleys 33.2% of the time compared to only 18.6% for the available habitat (Table 2.7). Dippers also selected areas where trees dominated the vegetation immediately adjacent to the stream on one (6.4% of the observations) or both (6.0%) sides of the stream compared to the available habitat (4.5% and 0.8%; P = 0.64 and P = 0.06, respectively; Table 2.8). Riparian canopy cover was positively associated

Table 2.6. Abundance (individuals 110 km of stream) of riparian-associated birds during 1992-1994 in 4-5th order Drift and Lobster creeks, Oregon Coast Range. Values are least-squared means from the analysis of variance model including stream order, basin, and cycle effects (n = 24 surveys, 309 km of stream).

American Dipper

Belted Kingfisher

Common Merganser

Great Blue Heron

-

SE

-

1992

3.1 A

1993 1994

Year

x

SE

x

SE

-x

SE

1.8

5.0A

1.0

0.5 A

0.7

1.2 A

6.8A

1.8

2.6 A

1.0

1.5 A

0.7

9.3 A

1.8

4.5 A

1.0

0.1 A

0.7

x

P

Green Heron

-

Wood Duck

Mallard

x

x

SE

-

x

SE

0.3

O.lOA

0.07

2.9 A

0.8

0.13 A

0.07

0.5 A

0.3

0.08 A

0.07

0.8 A

0.8

0

A

0.07

0.4 A

0.3

0.07 A

0.07

0.7 A

0.8

0.07 A

0.07

0.0657 0.2360 0.3854 0.2390 a column means with the same letters are not different (P > 0.05).

0.9445

0.1142

SE

0.5272

00

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19

Table 2.7. Streamside habitat characterizing sites used by and available to

riparian-associated birds in the central Oregon Coast Range, 1992-94. * indicates variables included in the logistic regression model", Appendix A contains a more detailed summary.

American Dipper

SE

X

n

Belted Kingfisher

Great Blue Heron

-x

-X

250

tree-dominated riparian zone (%) - one bank - both banks

riparian zone canopy cover (%) trees on the stream bank (%)

- one bank - both banks conifers on the stream bank (%) - one bank - both banks valley form (% constrained) - one bank - both banks land use (% managed forests)

- one bank - both banks distance to human activity (m)

152

SE

SE

X

72

SE

X

79

1120

12.8*

2.1

25.7

3.5

25.0*

5.1

44.3

5.6

30.4

1.4

82.0*

2.4

57.9

4.0

55.6*

5.9

41.8

5.5

59.3

1.5

2.9

27.0

3.6

31.9

5.5

34.2

5.3

25.7

1.3

10.4

1.9

5.3

1.8

6.9

3.0

6.3

2.7

7.1

0.8

5:l.3*

1.2

42.4

1.8

41.8

2.7

33.5*

2.2

43.9

0.6

6.4*

1.5

6.6*

2.0

2.8

1.9

2.5

1.8

4.5

0.6

6.0*

1.5

5.3*

1.8

0

0

2.5

1.8

0.8

0.3

0

0

0.7

0.7

0

0

1.3

1.3

0.2

0.1

0

0

0.7

0.7

0

0

0

0

0

0

conifer-dominated riparian zone (%) 30.4 - one bank - both banks

SE

available habitat

Mallard

41.6*

3.1

36.2*

3.9

29.2*

5.4

35.4*

5.4

42.4

1.5

33,.2*

3.0

17.1*

3.1

20.8*

4.8

15.2*

4.0

18.6

1.2

9.2

1.8

22.4

3.4

19.4

4.7

20.3*

4.5

21.6

1.2

78.8

2.6

56.6

4.0

61.1

5.7

62.0*

5.5

60.6

1.5

303

33

160*

29

295*

71

136

32

280

17

8 Species abundance and habitat features may vary among basin, stream order, and season. Presented means pool all observations whereas the statistical models assessing habitat selection first account for differences inherent to basin, stream order, and season before identifying habitat selection patterns. Consequently, the pooled means may mask more substantial differences.

20 Table 2.8. Variables distinguishing between used and available streamside habitat for American Dippers, Belted Kingfishers, Great Blue Herons, and Mallards in the Oregon Coast Range, 1992-1994. Wald X2 and P values are from logistic regression models fitted with indicator variables for basin, stream order, and season. Each set of variables remained after backward logistic regression eliminated others at a significance level = 0.10.

90% confidence interval on odds ratio

Species parameter standard estimate error Wald's x2

variable

odds

P

ratio"

lower

upper

American Dipper Intercept"

-3.935

0.450

76.6276

0.0001

Basinl"

0.992

0.221

20.2084

0.0001

2.70

1.88

3.88

Basinz"

-0.379

0.284

1.7797

0.1822

0.68

0.43

1.09

Basin3 b

0.135

0.253

0.2848

0.5936

U5

0.76

1.74

Order4 b

0.840

0.241

12.1852

0.0005

2.32

1.56

3.44

Order5 b

U46

0.238

23.2793

0.0001

3.15

2.13

4.65

Season"

0.780

0.174

20.0763

0.0001

2.18

1.64

2.91

tree-dominated riparian zone (%)

-one bank

-0.759

0.382

3.9461

0.0470

0.47

0.25

0.88

0.297

0.377

0.6202

0.4310

1.35

0.72

2.50

riparian zone canopy cover

(10% increments)

0.073

0.048

2.2815

0.1309

1.08

0.99

U6

trees on the stream bank(%)

- one bank

0.210

0.452

0.2164

0.6418

1.23

0.59

2.60

1.258

0.662

3.6084

0.0575

3.52

U8

10.45

0.209

0.191

1.2041

0.2725

1.23

0.90

1.69

0.764

0.218

12.2947

0.0005

2.15

1.50

3.07

0.519

0.275

3.5672

0.0589

1.68

1.07

2.64

- both banks

- both banks constrained valley form

-one bank - both banks streambank trees valley form

* constrained

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21 Table 2.8 (continued)


Species variable

parameter standard estimate error Wald's X2

P

odds ratio'

lower

upper

Belted KingfISher

Intercept"

·1.488

0.337

19.5

0.0001

Basinl b

-0.269

0.261

1.1

0.3032

0.76

0.50

1.17

Basin2 b

-0.715

0.283

6.4

0.0116

0.49

0.31

0.78

Basin3 b

-0.819

0.287

8.2

0.0043

0.44

0.28

0.71

Order4b

.1.023

0.261

15.3

0.0001

0.36

0.23

0.55

Order5 b

·0.343

0.229

2.2

0.1341

0.71

0.49

1.03

Season"

1.077

0.205

27.6

0.0001

2.94

2.10

4.11

distance to human activity (km)

-0.476

0.285

2.8

0.0947

0.62

0.39

0.99

trees on the stream bank (%) - one bank

0.567

0.379

2.2

0.1352

1.76

0.94

3.29

2.309

0.535

18.6

0.0001

10.07

4.18

24.26

-0.457

0.200

5.2

0.0224

0.63

0.46

0.88

-0.617

0.266

5.4

0.0202

0.54

0.35

0.84

Intercept"

·1.670

0.537

9.7

0.0019

Basinl b

-0.295

0.329

0.8

0.3693

0.74

0.43

1.28

Basin2b

-1.086

0.391

7.7

0.0055

0.34

0.18

0.64

Basin3 b

-1.323

0.424

9.8

0.0018

0.27

0.13

0.53

Order4 b

-0.113

0.357

0.1

0.7514

0.89

0.50

1.61

OrderS b

"().19O

0.368

0.3

0.6064

0.83

0.45

1.52

Season"

1.019

0.292

12.2

0.0005

2.77

1.72

4.48

distance to human activity (km)

..().649

0.529

1.5

0.2200

0.52

0.22

1.25

tree-dominated riparian zone (%) -one bank

.().71O

0.399

3.2

0.0751

0.49

0.26

0.95

..().638

0.374

2.9

0.0877

0.53

0.29

0.98

- both banks constrained valley form - one bank

- both banks Great Blue Heron

- both banks


Species

90% confidence

interval on odds ratio

parameter standard estimate error Wald's X2

variable

odds

P

ratio"

lower

upper

Great Blue Heron (continued) constrained valley form - one bank

-0.829

0.305

7.4

0.0065

0.44

0.26

0.72

-0.866

0.406

4.5

0.0330

0.42

0.22

0.82

0.802

0.339

5.6

0.0179

2.23

1.28

3.89

Intercept"

-0.897

0.519

3.0

0.0841

Basinl"

-1.920

0.432

19.8

0.0001

0.15

0.07

0.30

Basin2 b

-0.844

0.326

6.7

0.0097

0.43

0.25

0.74

Basins"

-1.789

0.408

19.2

0.0001

0.17

0.09

0.33

Ordera"

-1.634

0.417

15.4

0.0001

0.20

0.10

0.39

Orders"

-0.390

0.330

1.4

0.2376

0.68

0.39

1.17

Season"

1.147

0.277

17.1

0.0001

3.15

2.00

4.97

riparian zone canopy cover (10% increments)

-0.276

0.071

15.1

0.0001

0.76

0.68

0.85

constrained valley form

- one bank

-0.431

0.282

2.3

0.1263

0.65

0.41

1.03

-1.274

0.392

10.6

0.0012

0.28

0.15

0.53

0.132

0.415

0.1

0.7510

1.14

0.58

2.26

0.930

0.394

5.6

0.0182

2.53

1.33

4.84

- both banks distance to humans valley form

* constrained

Mallard

- both banks upslopes managed forests - one bank - both banks

a multiplicative likelihood of use given a l-unit increase in the value of a given variable. Odds 1 indicate a greater likelihood of use with an incremental increase in the value of that variable. b Indicator variable included in all models.


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23 with dipper habitat use (P = 0.13, Table 2.8). Compared to sites with overstory canopy cover 75%, respectively. The interaction between stream bank trees and constrained valley form explained additional variability in the data (P = 0.06). Three significant variables contributed to the model for habitat selection by Belted Kingfishers (X 2 =79, 11 df, P =0.0001, max. rescaled R2 =0.1155). Kingfishers were 4.2 to 24 times (90% CI) more likely to use an area with trees immediately adjacent to the stream on both banks (P =0.0001, Table 2.7 and Table 2.8) than reaches without

streamside trees. However, kingfishers were only 0.46 - 0.88 and 0.35 - 0.84 times (90%

CIon odds ratio) as likely to use reaches with a constrained valley form on one or both

sides of the stream (both P = 0.02, Table 2.8) compared to unconstrained reaches (odds

ratio = 1). They selected stream sections that were constrained on one or both sides

(36.2% and 17.1%, respectively) less often than were available (42.4% and 18.6%,

respectively). Kingfishers also used habitat that was slightly closer to human activity (x

=160 m, Table 2.7) than the available habitat (x =280 m, P =0.09, Table 2.8).

Presence of riparian trees, the valley form, and the distance to human activity

distinguished between areas used by Great Blue Herons and those available (X 2 = 47, 12

df, P

=0.0001, max. rescaled Rl =0.1050).

Herons were 0.3 - 0.7 and 0.2 - 0.8 times

(90% CIon odds ratio) as likely to use reaches that were constrained on one or both sides

of the stream than unconstrained reaches (P = 0.007 and P = 0.03, respectively, Table

2.8); they used less constrained valley forms than were available (Table 2.7). Herons

were 0.49 - 0.95 and 0.53 - 0.98 times (90%CI on odds ratio) as likely to be found where

the riparian-zone vegetation was.trees on one or both sides of the stream compared to

treeless riparian zones (odds ratio = 1). The interaction of the distance to humans and

constrained valley form also was significant (P = 0.02).

Three variables explained habitat use by Mallards (X2 = 89, 11 df, P = 0.0001,

max. rescaled R 2 =0.1850). Mallards were 1.3 to 4.8 times (90% CI) more likely to be

found where both adjacent upslopes were managed forests (odds ratio

=2.5, P =0.02,

Table 2.8) rather than another land use type (odds ratio = 1). The likelihood of use by

24

Mallards decreased (odds ratio = 0.68 to 0.85,90% CI) for each 10% increase in overstory canopy cover in the riparian area (odds ratio

=0.76, P =0.001).

Mallards also

were 15% to 53% as likely to be located on reaches that were constrained on both sides than in unconstrained reaches( 15% of Mallard observations vs.19% of random locations; odds ratio

=0.28, P =0.001).

Channel Unit Use and Selection

I located dippers most often in riffles (37%), rapids (27%), and pools (19%); and kingfishers were found perched over pools (47%), glides (31%), and riffles (16%). The available habitat was composed of riffles (57%), rapids (17%), glides (16%), and pools (10%). Dippers were located on steps more than expected and riffles less than expected. Kingfishers were found over pools more than expected and riffles less than expected (Table 2.9). No other species had adequate sample sizes to assess selection of channel units.

Stream Habitat Features Pool channel units were different between used and available habitat for dippers

=45,9 df, P =0.0001), kingfishers ('1.2 =35, 7 df, P =0.00(1), herons ('1. 2 =25, 8 df, P =0.0016), and Mallards ('1. 2 =24,8 df, P =0.0019). Pools used by dippers were more likely to be shorter (x =19 m vs. 76 m [Table 2.10], odds ratio =0.97, P =0.06), wider (odds ratio =1.12, P =0.04), and had larger substrate items (odds ratio = 1.36, P =0.06, Table 2.11) than the available pools (odds ratio = 1). Great Blue Herons and Mallards ('1. 2

selected pools that were more open and were in secondary channels. Both species were observed in secondary channel pools 11% and 8% of the time even though these pools comprised only 2% of the available habitat. Consequently, stream segments with pools adjacent to the primary channel increased the likelihood of use by herons and Mallards by 3 to 34 and 1.4 to 19 times (90% CI; odds ratios =9.7 and 5.2; P =0.003 and P

=0.04,

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25 Table 2.9. Channel unit use by American Dippers (n =95) and Belted Kingfishers (n = 32) in Drift and Lobster creeks in the Oregon Coast Range, 1992-1994. Proportion of available habitat calculated from the area of 269 channel units (total length = 12,273 m, total area =91,047 rrr').

proportion" channel unit

number of observations

of available proportion channel of observed units use

95% confidence limit on observed use lower

upper

selection"

American Dipper pool

18

0.098

0.189

0.093

0.311

0

glide

7

0.162

0.074

0.018

0.169

0

riffle

35

0.569

0.368

0.237

0.503

rapid

26

0.167

0.274

0.158

0.404

0

cascade

3

0.003

0.032

0.001

0.110

0

step

.§

MOO

0.063

0.013

0.155

+

95

100

100

0.031

0.004

0.198

Total

Belted Kingf"lSher beaver pond

1

pool

15

0.098

0.469

0.231

0.689

+

glide

10

0.162

0.313

0.116

0.542

0

riffle

5

0.569

0.156

0.027

0.370

rapid

1

0.167

0.031

0.004

0.198

cascade

0

0.003

step

Q

Q.OOQ

0

Total 32 100 100 "Proportion of channel units represents expected dipper observations if dippers used each habitat in exact proportion to availability. b Channel units used less than (-), more than (+), or in proportion (0) to expected use with the assumption of proportional use.

26

Table 2.10. Stream habitat characterizing sites used by and available to

riparian-associated birds in the Oregon Coast Range, 1992. * indicates variables included

in the logistic regression model", Appendices Band C contain a more detailed summary.

pool

American Dipper

Belted Kingfisher

Great Blue Heron

-x

-x

-

SE 21

n=

SE

SE

x

-x

37

60

available habitat

Mallard

SE

-

SE

x

37

342

channel unit length (m)

19.1*

3.7

109.3

32.1

123.1

44.8

76.3

27.9

76.0

9.7

channel unit width (m)

9.9*

1.1

14.0

0.8

11.1

1.1

13.7

1.1

11.0

0.4

40.0

4.2

59.0

6.9

63.0

9.6

56.3

6.8

56.6

2.2

channel form (% locations in secondary channel)

4.8

4.6

1.7

1.7

10.8*

5.1

8.1*

4.5

2.0

0.8

substrate size

7.5*

0.2

7.0

0.3

6.4

0.3

6.5

0.4

6.5

0.1

11.9

3.4

2.5

0.7

3.2

1.2

4.7

3.2

8.2

2.0

2.4

1.4

0.8*

0.2

2.4

0.6

0.7

0.2

4.5

1.0

37.4

5.6

3.2

21.2*

3.6

19.4*

3.0

32.5

1.4

channel unit depth (cm)

number of exposed substrate items (# 1100 m2) large wood (# 1100 m2) stream shading (%) glide

23.3

28

n=

33

17

11

337

channel unit length

13.5

1.5

24.9*

5.9

13.9

2.7

17.3

2.0

15.0

0.7

channel unit width

7.4

0.9

10.9

1.1

11.1

1.6

11.5

1.5

8.3

0.3

channel unit depth

25.0

1.8

27.6

2.9

25.9

2.0

30.0

4.0

25.5

0.7

channel form

3.6

3.5

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

substrate size

7.6

0.2

7.4*

0.3

7.5

0.5

8.1

0.3

7.5

0.1

20.1

4.5

4.7*

1.5

9.5

3.5

3.9

1.8

30.9

5.0

2.2

1.1

1.1

0.3

2.0

1.2

1.4

0.5

4.4

0.7

44.6

5.2

27.9

4.2

29.0

9.4

21.5

3.4

37.2

1.5

exposed substrate large wood stream shading

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rime

American Dipper

Belted Kingfisher

Great Blue Heron

-x

-x

-x

SE 59

n=

SE 14

SE

MaIlard

-x

4

SE

available habitat

x

4

SE 344

channelunitlen~

14.8

1.4

20.7*

3.7

21.7

8.2

15.9

3.7

14.2

0.6

channel unit width

6.4

0.6

8.8

1.6

9.6

2.7

15.4

4.0

8.0

0.3

channel unit depth

16.1

1.2

22.9*

4.0

21.3

5.9

21.3

5.2

16.5

0.5

channel form

1.7

1.7

0

0

0

0

0

0

1.5

0.6

substrate size

7.5

0.1

7.4

0.3

6.5

1.0

8.5

0.5

7.6

0.1

63.2

16.4

57.3

41.0

7.9

4.2

12.1

3.3

57.3

5.2

0.3

0.7

0.5

52.1

52.1

0.0

0.0

6.7

2.3

3.9

34.7

9.1

18.8

10.3

10.0

3.5

36.9

1.5

exposed substrate large wood

1.4*

stream shading rapid

43.2

45

12

n=

channel unit length

6.3

2.1

8.5

1.1

channel unit width

6.5

1.3

10.0

1.0

channel unit depth

16.7

3.4

22.1

1.7

channel form

0.0

0.0

0.0

0.0

substrate size

8.0

0.3

8.4

0.1

68.6

17.9

37.9

8.5

2.6

1.3

2.0

0.7

42.9

9.3

26.5

4.4

exposed substrate large wood stream shading cascade

3

n=

11

channelunitlen~

20.0

15.0

11.5

3.0

channel unit width

13.2

4.6

11.1

1.5

channel unit depth

35.0

7.6

16.8

2.5

channel form

0.0

0.0

9.1

8.7

substrate size

8.3

0.3

8.4

0.2

25.4

11.4

18.9

5.4

1.0

0.6

0.6

0.4

63.3

8.8

45.9

9.4

exposed substrate large wood stream shading


step

American Dipper

Belted Kingfisher

Great Blue Heron

-x

-x

-x

SE

SE

SE

Mallard

-x

SE

available habitat

-

6

n=

SE

x 19

channel unit length

2.1

1.2

3.8

1.6

channel unit width

6.6

2.5

7.8

1.2

channel unit depth

28.3

13.3

15.6

3.8

channel form

0.0

0.0

0.0

0.0

substrate size

8.2

0.4

8.9

0.1

exposed substrate

75.1

40.8

107.0

45.6

large wood

20.1

13.2

99.7

90.4

stream shading

44.2

11.4

40.7

6.3

a Species abundance and habitat features may vary among basin, stream order and season. Presented means pool all observations whereas the statistical models assessing habitat selection first account for differences inherent to basin, stream order, and season before identifying habitat selection patterns. Consequently, the pooled means may mask more substantial differences.



29

Table 2.11. Variables distinguishing between used and available stream channel units for American Dippers, Belted Kingfishers, Great Blue Herons, and Mallards in the Oregon Coast Range, 1992. Wald 'l and P values are from logistic regression models fitted with indicator variables for basin, stream order, and season. Each set of variables remained after backward logistic regression eliminated others at a significance level = 0.10.


Species parameter estimate

standard error

Wald's

X2

P

Intercept"

-9.37

2.37

15.57

0.0001

Basinl"

1.82

0.71

6.52

0.0106

6.15

1.91

19.82

Basin2b

-0.68

1.20

0.31

0.5742

0.51

0.07

3.68

Basin3 b

-0.49

0.97

0.25

0.6143

0.61

0.12

3.05

Ordera"

3.48

1.56

4.92

0.0264

32.44

2.46

427.27

OrderS b

3.80

1.39

7.37

0.0066

44.68

4.48

446.10

Season"

0.34

0.55

0.37

0.5417

1.40

0.56

3.53

Length

-0.03

0.01

3.46

0.0626

0.97

0.94

1.00

Width

0.11

0.05

4.19

0.0405

1.12

1.02

1.23

Substrate Size

0.30

0.15

3.63

0.0567

1.36

1.04

1.76

Intercept"

-3.33

0.59

30.78

0.0001

Basin1 b

1.41

0.49

8.12

0.0044

4.09

1.82

9.23

Basin2b

0.63

0.51

1.47

0.2240

1.88

0.80

4.40

Basin3 b

0.52

0.52

0.97

0.3245

1.68

0.71

4.01

Ordere"

1.10

0.43

6.50

0.0107

3.00

1.48

6.09

OrderS b

1.05

0.42

6.19

0.0128

2.85

1.43

5.69

Season"

0.19

0.29

0.40

0.5253

1.21

0.74

1.97

Pieces of wood /100 m 2

-0.06

0.03

3.01

0.0826

0.94

0.89

1.00

variable

odds

ratio"

lower

upper

American Dipper Pool

Riffle

30

Table 2.11 (continued)


Species

parameter estimate

standard error

Wald's

X2

P

Intercept"

-1.47

0.50

8.43

0.0037

Basinl"

-0.46

0.43

1.12

0.2889

0.63

0.31

1.29

Basin2 b

-0.85

0.46

3.39

0.0653

0.43

0.20

0.91

b

-0.38

0.45

0.71

0.3994

0.68

0.32

1.44

Order4 b

-1.23

0.53

5.18

0.0227

0.29

0.12

0.71

Order5 b

0.12

0.34

0.11

0.7327

1.13

0.64

1.99

Season"

0.89

0.31

7.96

0.0048

2.43

1.45

4.08

Wood I 100m2

-0.12

0.08

2.17

0.1405

0.89

0.78

1.01

Intercept"

-0.38

1.24

0.09

0.7594

Basinl"

-0.53

0.66

0.62

0.4293

0.59

0.20

1.77

Basin2 b

0.11

0.57

0.03

0.8454

1.12

0.44

2.87

Basins"

-0.07

0.62

0.01

0.9174

0.94

0.33

2.63

Order4 b

-0.61

0.58

1.08

0.2967

0.54

0.21

1.43

Order5 b

-0.33

0.49

0.43

0.5074

0.72

0.32

1.63

Season"

0.49

0.38

1.60

0.2045

1.63

0.87

3.09

Length

0.02

0.00

3.10

0.0742

1.02

1.00

1.03

Substrate Size

-0.24

0.12

3.66

0.0557

0.79

0.64

0.97

Exposed rocks 1100 m2

-0.03

0.02

2.85

0.0912

0.97

0.93

1.00

variable

odds ratio'

lower

upper

Belted Kingf"lSher Pool

Basin3

Glide





Species variable

parameter estimate

standard error

Wald's

X2

P

odds ratio'

lower

upper

Belted. Kingf"lSher (continued) Riffle

Intercept"

-9.54

2.19

19.00

0.0001

Basinl"

1.78

1.26

1.98

0.1590

5.92

0.74

47.23

Basinz"

1.88

1.30

2.08

0.1490

6.55

0.77

55.77

Basins"

1.85

1.33

1.95

0.1629

6.36

0.72

56.33

Order4b

2.19

0.94

5.45

0.0196

8.94

1.91

41.80

OrderS b

1.28

0.88

2.10

0.1476

3.59

0.84

15.37

Season"

1.27

0.67

3.61

0.0574

3.57

1.19

10.74

Length

0.05

0.02

4.14

0.0419

1.05

1.01

1.10

Depth

0.09

0.03

8.84

0.0029

1.10

1.04

1.15

Intercept'

-2.41

0.62

15.00

0.0001

Basinl b

0.11

0.50

0.05

0.8223

1.12

0.49

2.56

Basin2b

-0.06

0.54

0.9118

0.94

0.38

2.32

Basin3b

-0.07

0.55

om om

0.8939

0.93

0.37

2.33

b

Order4

1.02

0.46

4.71

0.0299

2.76

1.28

5.96

Orderd"

0.30

0.50

0.34

0.5579

1.34

0.59

3.08

Season"

0.63

0.37

2.87

0.0898

1.88

1.02

3.46

Shade (l0% increments)

-0.27

0.08

9.99

0.0016

0.77

0.67

0.88

Secondary Channels

2.27

0.76

8.85

0.0029

9.66

2.76

33.86

Great Blue Heron Pool


90% confidence

interval on odds ratio

Species

parameter estimate

standard error

Wald's

X

P

Intercept"

-1.56

0.58

7.12

0.0076

Basinl"

-0.95

0.53

3.11

0.0778

0.39

0.16

0.94

Basinz"

-0.61

0.51

1.40

0.2359

0.54

0.23

1.27

Basin3b

-0.58

0.53

1.17

0.2782

0.56

0.23

1.35

Order4b

-0.65

0.58

1.26

0.2615

0.52

0.20

1.36

OrderSb

0.36

0.45

0.60

0.4364

1.42

0.67

3.03

Season"

0.72

0.37

3.n

0.0520

2.06

1.12

3.79

Shade (10% increments)

-0.21

0.09

4.90

0.0268

0.80

0.69

0.95

Secondary Channels

1.65

0.79

4.25

0.0392

5.20

1.40

19.34

variable

2

odds

ratio"

lower

upper

Mallard Pool

a multiplicative likelihood of use given a l-unit increase in the value of a given variable. Odds 1 indicate a greater likelihood of use with an incremental increase in the value of that variable.

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33

respectively). Herons and Mallards used stream segments where shaded from the

overhead vegetation was less than that available (21% and 19% vs. 33%). A 10%

increase in stream shading decreased the likelihood of use by approximately 23% and

20% for herons and Mallards (P

=0.002, and P =0.03, respectively; Table 2.11).

Glide channel units usedby kingfishers were different than available glides (X 2 =

24, 9 df, P =0.0048; Table 2.11). The likelihood that a kingfisher would use a glide

increased with its length (odds ratio

=1.02, P =0.07).

However, the likelihood of

kingfisher use decreased with increasing substrate size class (odds ratio =0.8, P =0.06)

and the number of exposed substrate items (odds ratio =0.97, P =0.09).

Riffles used by dippers and kingfishers were different than those available (X2 =

24, 7 df, P =0.0010 and X2 =18,8 df, P =0.0245; respectively). The likelihood of dipper use decreased with an increase in the number of pieces of large wood in the riffle (odds

=0.94, P =0.08) compared to the available habitat (odds ratio =1). Kingfishers used riffles that were longer (odds ratio =1.05, P =0.04) and deeper (odds ratio =1.1, P =0.003) than the average riffle (odds ratio =1). ratio

DISCUSSION

Distribution

The distribution and abundance of all riparian-associated birds were different among stream basins and stream orders. Factors explaining these differences include species-specific behavior and basin and stream order differences in geomorphology, topography, hydrology, and riparian zone vegetation. Differences in abundance among basins likely reflected the differences in the geomorphology of those basins. Only dippers were more abundant in Drift Creek than in other basins, and Drift Creek was the most isolated and the highest-gradient basin. Mallards were more abundant in Lobster Creek than in other basins, and Lobster Creek was a low-gradient stream with many pools and slow-water channel units. The juxtaposition of grass-dominated agricultural lands and

34 these low-gradient streams in Lobster Creek may be important for Mallard brood rearing because most of the groups I observed were adult females with young. Regardless of the underlying geomorphic and management differences among the four basins, kingfishers were similarly abundant throughout the study area. However, kingfisher abundance may have been ameliorated by a number of factors because they will readily use a number of different substrates for nesting burrows. These include road cuts (Bent 1940) along the extensively-roaded study area, as well as cut-banks along the stream (Davis 1982) and banks created by headwall failures (pers. obs.). In addition, they can range a great distance from nest sites and may nest up to 2.4 km from the water (Hamas 1974, Prose 1985). The abundance of riparian-associated species was different among stream order and likely reflects the behavior of the birds I observed. Mallards and mergansers often used streams as loafing and brood-rearing habitat, and their abundance was greatest lower in the basins. Both the frequency and extent of micro-habitats with lower stream velocities was greater here, allowing birds to expend minimal energy to maintain their position. However, dippers, kingfishers, and herons were observed actively foraging and their abundance reflected their selection of foraging (kingfishers) as well as breeding (dippers) habitat. Similarly, herons find more suitable foraging micro-habitat, such as off-channel pools, in the larger streams lower in the basins.

Abundance

Riparian-associated birds in the Oregon Coast Range were generally less abundant than elsewhere in North America. Dippers were over 4 times more abundant in Montana and Colorado. Sullivan (1973) and Price and Bock (1983) report breeding densities>1.0 nests I km and Ealey (1977) observed 1.2 birds I km compared to 0.2-0.5 birds I km in

our study. The 5th-order reach of Drift Creek, with the most abundant dipper population, was marginally comparable (i =0.97 birds I km, SE =0.13, n = 12 surveys). Parsons (1975) found 1-4 dippers I km during the winter in the Oregon Cascades. The breeding density of Eurasian Dippers (c. cinelus) in Europe averaged >1 adult I km (Ormerod et al.


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35 1985~

Daulne 1990, Vickery 1991). Availability of nest sites in our study area may have

limited the overall abundance of dippers (see Chapter 3). Streams where I saw dippers often had nests nearby. However, I rarely saw dippers in streams that contained no suitable nest sites, regardless of dle apparent ecological similarity to streams where dippers where present. Abundance of kingfishers in fifth and sixth-order streams was nearly 1 individual

I km of stream, whereas all other species were less than half that abundance. Breeding densities in similar sized streams!in Pennsylvania were comparable (Brooks and Davis 1987); however, in Ohio, breeding densities were nearly four times larger (Davis 1982). Studies of kingfishers in mountainous habitat are scant. Overall, I saw slightly more than one group of riparian-associated species for each kilometer of stream surveyed but no single species was very abundant. Although I believe there is no alternative way to sample this community, future research must expect the labor-intensive nature of these studies. Also, abundance of each species was likely biased by the probability of encountering, and identifying them. Although I did not directly quantify this bias, I offer this assessment. Dippers were likely to be nearly censussed. They seldom leave the course of the stream (Kingery 1996), and did not avoid human contact. Kingfishers and herons, however, occasionally would attempt to leave the area quietly and some observations could have been missed by an observer. Moreover, the low incidence of mammals in our study likely reflects the bias of our daytime surveys and not the relative abundance of these species.

Streamside Habitat Association

Dippers', kingfishers', herons', and Mallards' selection of streamside habitat was disproportional to availability, and the valley form was the only factor important to all four species. Dippers were associated with streams with riparian zones and stream banks dominated by trees on both sides. This was especially important because dippers were more abundant in the smaller, high gradient streams, where forests managed for timber

36

production were common in the Oregon Coast Range. Constrained valley forms also were important predictors of dipper use. Kingfishers were associated with the presence of trees on the stream banks, yet these features occurred 30% of observed use and >56% of the available habitat. While they may use

disproportionately fewer riffles, riffles provide foraging areas.

Kingfishers strongly selected pools and avoided riffles in this study. Conversely,

foraging kingfishers selected riffles, rather than pools in Pennsylvania and Ohio (Davis

1982, Brooks and Davis 1987); Specifically, the downstream tail-out transition to pools

within riffles were selected (Brooks and Davis 1987). Although seemingly contradictory,

these observations are consistent in that the kingfishers were responding to fish

distributions. Brooks and Davis (1987) observed fish abundance was greatest in the

downstream portion of riffles, and I believe their study streams may have been lower

gradient than those in my study. Most of my observations were of birds perched over the

stream and presumably foraging. The fourth- and fifth-order streams I evaluated were

high gradient (1-3%) with higher surface turbulence and visual disturbance than in

Pennsylvania or Ohio. Moreover, salmonids, primarily juvenile coho salmon

(Oncorhynchus kisutch), were more abundant in pools (phillips 1986, Bisson et al. 1988, Schlosser 1991).

Stream Habitat Association

Channel unit length, width, and depth, secondary channels, wood, substrate size, exposed substrate items, and stream shading were useful in discriminating between pools, glides, and riffles that were used versus those available; however, many confidence

----------------

38 intervals on the odds ratio indicated marginal statistical significance (i.e., spanning or approaching 1.0). Channel heterogeneity and structural complexity were important features. Pools that were in a secondary or side channel with less shade were more likely to be used by Mallards and Great Blue Herons. Generally, these pools had sustained flow during the winter months when stream flow was highest. However, as flow volume decreases throughout the summer, the pools were partially or entirely cut off from the main channel, trapping prey or creating a current-free loafing site. Belted Kingfishers strongly selected sites with trees on both stream banks, and they were located above pools more than expected based on channel unit availability. However, kingfishers were less likely to use pools with more wood in them. This paradox may be the result of historical harvest extending to the stream thereby, eliminating recruitment of large wood during the past two decades. Alternatively, the increase in channel unit complexity because of wood may reduce kingfisher foraging efficiency (e.g., Kelly 1996) and high complexity units would be less frequently used. In addition, kingfishers were located above riffles less frequently than expected, but the likelihood of finding them over a riffle increased with each ern of depth. Finally, I recognize a number of limitations of this study. I chose the four study basins subjectively, representing a non-random sample of the Oregon Coast Range. Consequently, inference of abundance to larger geographic scales beyond these basins should be done with caution. Although several important habitat variables were identified by the logistic regression models, none explained >25% of the observed variability (R2). In addition, many models had low statistical power. Although the majority of factors identified by the habitat selection models contributed to the model's fit and as a whole were important descriptors of the habitat-use patterns I observed, they individually were not different from a zero effect (i.e., 90% CIon the odds ratio included or approached 1.0). In part, this may be attributed to the natural variability in the environment, variable habitat selection patterns for each species, and variability among the stream orders and basins I studied. Further improvement of sampling techniques, habitat quantification, and focusing on a more specific spatial and temporal scale may improve the study's explanatory power but also may decrease the generality.


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39

MANAGEMENT IMPLICATIONS Managers should consider the basic ecological information on species composition, abundance, and habitat associations of riparian-associated species when refining the goals and objectives of riparian zone management. Monitoring programs to assess populations of these species must be sensitive to the potential effects of stream order, basin, and season. The low abundance and sparse distribution of these species in the Oregon Coast Range provide additional challenges in evaluating the cumulative effects of management within and among basins. Population-level responses may be difficult to quantify at the scale of most silvicultural experiments (e.g., 200-m long riparian management zones). Monitoring plans and riparian zone management attempts should consider a large spatial (e.g., watersheds) and temporal extent to detect species presence and account for differences in abundance among basin and order. Monitoring at smaller spatial scales could be inadequate and allow cumulative impacts on the entire watershed to go undetected. I strongly recommend an a priori assessment of study objectives and statistical power to evaluate the potential success of the project. Trees on the bank.immediately adjacent to the stream where associated with increasing likelihood of use by dippers and kingfishers, the two most abundant species. Management regimes and silvicultural prescriptions should retain or establish streamside trees. Riparian zones dominated by tree species were positively associated with dippers, and were present at 95% of my dipper observations. However, appropriate riparian buffer strip widths need to be evaluate at a variety of spatial scales. Few attributes were different between used and available channel units, and most significant variables would be difficult to successfully manage (e.g., substrate size). Riparian zone management should include aspects that maintain stream channel heterogeneity, allow the stream to interact with the flood plain, and include secondary and alternate channels within the riparian forest. Policies that encourage channel heterogeneity and retain large wood also would benefit riparian-associated species by providing varied habitats, although kingfishers were negatively associated with wood in pools.

40 Wildlife associated with riparian areas are important resources. As riparian areas

become more intensively managed, the challenge will be to create strategies that do not compromise the ecological requirements of riparian-associated species. Efforts to monitor and maintain stream systems with good water quality and sustainable populations of aquatic invertebrates and vertebrates should protect the resources needed by riparian obligates. Conservation strategies developed for terrestrial riparian wildlife, fish, and aquatic habitat (e.g., Bisson et al. 1992, FEMAT 1993, Thomas et al. 1993:427-482) that focus on the restoration and maintenance of physical and biological integrity of aquatic systems (Karr et al. 1986, Karr 1991, Naiman et al. 1992) should protect riparian-associated species as well.

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Chapter 3. Nest-site Selection and Productivity of American Dippers

INTRODUCTION

Habitat selection is a complex product of many factors and is influenced by life history traits, evolutionary history, inter- and intra- specific competition, territoriality, predation, and foraging strategies (Cody

1985~,

Morrison et al. 1992). Assessing habitat

selection at an arbitrary spatial scale may have a profound influence on the conclusions drawn from a study (Allen and Starr 1982:259, Wiens 1985). Wiens (1985) noted that an investigator was likely to miss the dynamics that produce the patterns we observe by focusing on a broad scale. Conversely, focus on a small group of individuals in a local area may fail to detect important habitat characteristics that influence species on a landscape or biogeographic scale (Wiens 1985). The issue of scale is further confounded by the fact that each smaller scale is constrained or dependant upon the larger scale (Johnson 1980). Hierarchical approaches (Johnson 1980, Allen and Starr 1982) of examining multiple spatial scales that are based on biologically relevant scales (e.g., Morris 1987) may reveal selection patterns and provide an integrated insight into species' habitat selection. Birds display habitat selection at many different spatial scales when selecting a place to nest. Those that have specific nest-site requirements (e.g., cavities in trees) must assess likely habitats for those requirements (Cody 198512:41) within a selected home range. Moreover, micro- and macro-habitat characteristics may influence reproductive output providing an evolutionary mechanism for selection. Specific micro-site features may confer an advantage in reproductive potential (Calder 1973; Austin 1974, 1976; Walsberg 1985). However, specific nest-site requirements may limit the habitat available and may increase species' susceptibility to ecological or anthropogenic disturbances. Along riparian zones in the Pacific Northwest, ecological information on species associated with streams and their habitat association is lacking (Anthony et al.

1987~,

McGarigal and McComb 1988) but essential for ecologically-sound management. American Dippers (Cinclus mexicanus) are the most abundant resident riparian-obligate

42 bird in the managed forests of the Oregon Coast Range (OCR)(Chapter 2). The species is widely distributed in mountainous regions of western North America from Alaska to southern Mexico (Bent 1948, Van Tyne and Berger 1959, Kingery 1996). Nests generally are placed over or directly above the edge of the stream, are inaccessible to predators, and are often sheltered from the weather (Hann 1950, Price and Bock 1983, Kingery 1996). Nests are hut-shaped, composed of moss, and enclosed with a domed roof (15-25 em diameter). They are placed typically on a cliffs narrow ledge; in a cavity of a horizontal, hollow log; under or within the support structure of bridges (Kingery 1996); or in nest boxes (lost 1970, Hawthorne 1979). Reproductive success may vary with nest-site quality (Price and Bock 1983). I evaluated nest-site selection of dippers in the central OCR at three spatial scales: the physical placement of nests (micro-habitat, approximately 0.25-1.0 m'), the nests' immediate surroundings (macro-habitat, approximately 1-10 m 2) , and the streamside or riparian zone habitat (>100 m'). I also evaluated differences in reproductive success related to nest-site characteristics. Because nest-site availability previously had been suggested as a factor limiting dipper populations, I experimentally increased the number of available nest sites in one stream and subsequently monitored it and an unaltered stream for four years. Specifically, I tested the null hypotheses that 1) macro- and micro-habitat characteristics did not differ between dipper nest sites and available sites, 2) streamside habitat at dipper nests was not different from randomly-selected locations, 3) reproductive success was not correlated with any feature of the nest or nest-site habitat at the micro-, macro-, or riparian-zone scales and 4) increased availability of nest sites will not affect the number of breeding pairs. I also assessed geographic differences between the Coast and Cascade Ranges in nest-site habitat characteristics.



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43

METHODS Study Area In 1994, I located dipper nests along streams in the central Oregon Coast Range and the Oregon Cascades. In the central Coast Range, I surveyed Drift (44 ° 25'N, 123° 50W) and Lobster creeks (44° 15'N, 123° 40'W), as well as all adjacent streams within a 10-km radius of them (Fig. 2.1). Ii These basins were in Benton, Lane, and Lincoln counties and drained into the Alsea and Siuslaw rivers 6-23 km east of the Pacific Ocean. Streambed elevation ranged from 3 to 365 m. In Lane County, I surveyed Cummins and Bob (44° 15' N latitude), Rock (44° 10' N), and Cape creeks (44° 8' N) upstream from the Pacific Ocean. In the Oregon Cascades, I surveyed the North Fork of Silver Creek within Silver Creek Falls State Park (440 50' N, 122° 40' W) in Marion County; Mack, McRae, and Lookout creeks in the H. J. Andrews Experimental Forest (IDA, 44° 15' N, 123° 15' W), and Tidbits Creek and Blue River on the northwest border of the IDA in Lane

County. The topography was steep with moderately flat valleys. Stream gradient averaged 30 em in diameter, bridges, and all cliffs and steep banks within 5 m of the water's edge for sites capable of supporting a nest (hereafter, nest site). I located and characterized all active nests, old nests, and all potentially suitable but currently unused nest sites. I distinguished among sites with known dipper use where I observed birds using the nest during this study or those with fresh fecal material. Nests were classified as unknown use when nests were built prior to the study and had unknown history. Unused sites had no observed nests. I defined an unused nest site as any site I judged

capable of holding a dipper nest. I established minimum criterial for sites on cliffs requiring they have a near-vertical cliff area of~3 m 2, were ~l m above the ground, were ~5

m from the stream, and had a ledge, thick (>2 em) moss covering, or physical

configuration that would support a nest. Unused sites in logs needed to have a cavity larger than 10-cm x 10-cm or a platform where a nest could be placed. During 1993-1995, I examined all nests on Drift and Lobster creeks at least weekly, noting the number of eggs or chicks. I estimated hatching dates based on nest initiation dates and chick growth characteristics (Sullivan 1973). I recorded nest, egg, and fledging success, and identified sources of nest failure whenever possible.

Artificial Nesting Structures In August 1993, I selected two reaches, 8-1D-km long, that were of similar size and gradient; one each from Drift and Lobster creeks. I randomly selected one reach to be modified, Drift Creek, and identified the other, Lobster Creek, as the unaltered, or control, reach. I constructed seven nest structures (3 nest boxes, 2 log cavities, and 2 cliff ledges) along Drift Creek. I constructed nest boxes (Appendix E) similar to lost (1970) and Hawthorne (1979). I affixed them with screws or waterproof epoxy to the inside of a 2.7-m dia. culvert, a fish ladder wall, and a log spanning the stream. After the box on the fish ladder was vandalized in 1994, I moved it approximately 50 m upstream and placed


I


45 it in the middle of a 115 x 123 em sheet of plywood which was subsequently screwed to an abandoned bridge abutment composed of large Douglas-fir logs. I created cavities in the ends of two logs extending over the stream with a brace and bit. Minimum dimensions of these cavities were 15 x 19 x l S em (height x width x depth). I constructed two ledges with a hammer and chisel on sandstone cliffs lacking a mossy covering. I glued two additional nest boxes to the underside of flat-bottomed, concrete bridges in August 1994.


I categorized nest and potential nest sites into 5 groups based on their substrate (hereafter referred to as nest type): nests in boxes that I provided, on rock or moss ledges, under bridges, in cavities or hollows in logs (log cavities), and associated with stream bank roots or rootwads. I used an analysis of variance to compare nest density among geographic areas. I considered multiple nests in close proximity «5 m) as a single breeding attempt and one active nest when calculating nest density. I used linear regression to assess the annual change in the number of breeding dippers after the construction of artificial nest sites in the treated and untreated streams. I used logistic regression to compare 1) nest, micro-habitat, and macro-habitat characteristics of nests with known versus unknown use, 2) micro-habitat and macro-habitat variables at used versus unused sites, and 3) streamside habitat at used versus randomly-selected locations. I defined nest characteristics as the height, width, and depth of both the nest entrance and the entire nest. Micro-habitat was composed of the height, width, and depth of the supporting ledge; the average thickness of moss on the ledge or cliff; and indicators for Whether or not the nest was sheltered from the weather, accessible to avian predators, accessible to ground predators and the presence of a ledge or platform (10 x 10 em minimum). I defined macro-habitat as the cliff height and length, vertical cliff area, cliff slope or verticality, height of ledge or nest above the ground or streambed, horizontal distance from the margin of the stream at winter base flow to the nest [hereafter, setback distance], and for log cavity nests, the diameter of the

46

log, whether it was coniferous or not, and predator reach distance. Predator reach distance was equal to the height of the nest above the ground for nests placed back from the stream's edge. For nests hanging over the stream, it was the hypotenuse of a right triangle with the nest height and the distance to the shore as sides. I used predator reach distance only for logs because I noted many logs were relatively close to the ground or stream yet isolated by hanging out over the stream. I also characterized the riparian zone or streamside habitat at all sites and at 506 random locations in Drift and Lobster creeks according to the valley form, adjacent land use, riparian zone and stream bank vegetation, overstory canopy cover, and the distance to human activity (Chapter 2, Table 2.1). I used a logistic regression analyses with a forward selection routine to build each model to assess nest-site habitat selection. At each step, all variables under consideration were evaluated, and the variable that contributed the greatest explanatory power (greatest reduction in deviance) was added to the model. I terminated model-building when the additional variable did not improve the model's explanatory power by a drop in deviance, P ~ 0.15. I used a liberal significance level to enter the model because more conservative levels often fail to identify variables known to be important (Hosmer and Lemeshow 1989:86). I compared competing models with Akaike's Information Criterion (AlC) and selected the model with the lowest score. All models met the Hosmer and Lemeshow goodness-of-fit test(P > 0.05, Hosmer and Lemeshow 1989). I tested all first-order interaction combinations of the significant variables for each model after the initial variable selection. For each nest type, I compared micro- and macro-habitat characteristics (Table 3.1) at sites where I found nests to those identified as potential, unused nest sites. I used two models to compare habitat only at cliff nest sites. Similarly, I identified variables that distinguished between riparian zone or streamside habitat where I located nests versus locations selected at random. I included three indicator variables, one for basin and two for stream order, in all regression models for selection of riparian habitat because my objective was to examine habitat selection patterns after accounting for any effects of the two stream basins and three stream orders (Strahler 1957, see Chapter 2). All odds ratios from logistic regression analyses are reported relative to a base comparison, that is, an odds ratio = 1.


I


47 Table 3.1 Micro- and macro-habitat variables considered in logistic regression models to discriminate between used and unused American Dipper nest sites for three nest types in the Oregon Coast Range, 1994. The presence of a ledge and accessibility to ground predators were omitted from the analyses because all values were the same for used nests.

nest substrate types Variable

ledges

ledge length

micro-

ledge width

micro-

ledge height (clearance)

micro-

mean moss thickness

micro-

cliff height

macro-

cliff length

macro-

cliff verticality" (degrees from horizontal)

macro-

cliff vertical area

macro

height of nest above the ground

bridges

log cavities

macro-

x

x

winter set back distance

macro-

x

x

sheltered from the weather

micro-

x

x

accessible to avian predators

micro-

x

x

cross member angle"

x

log type (coniferous or hardwood)

x

log diameter

x

predator reach distance x 0 "Ninety degrees is exactly vertical, cliffs 90 0 slope out over the stream's edge. b The acute (s900) angle formed by the 1) load-bearing supports that are parallel to the long axis of the bridge, and 2) the central stabilizing cross-member, which is often parallel to the bridge abutments as well as the stream (Fig. 3.1).

48

stream

cross member angle

;

;

Nest

;

.:

;

Figure 3.1. Top view of a typical bridge crossing a mountain stream in the Oregon Coast Range. Bridge decking has been removed revealing the support beams, cross member, and typical American Dipper nest location. = cross member angle ~Oo ).

e

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49 I calculated daily nest and brood survival (Mayfield 1961, 1975) for the nests I intensively monitored. I compared survival among basins, nest types, and between natural and artificial sites using Hensler's (1985) techniques. I calculated the mean and total number of chicks that fledged each year for each site, and used Spearman's rank correlation to relate reproductive performance to micro- and macro-habitat characteristics (Table 3.1), streamside habitat characteristics (Table 2.1), and nest attributes (listed above).

RESULTS

I surveyed 181 Ian in seven basins in the Coast Range and found 50 nests and 42 potential, unused sites. I found 20 nests on ledges, 11 nests under bridges, 16 nests in logs, and 3 nests associated with rootwads. In addition, I identified 20 sites on ledges, 11 sites under bridges, 7 logs with cavities or platforms, and 4 sites associated with rootwads that were unused and had the potential to hold a nest. In four streams (>22 km) along the coast, I found 2, 6, and 3 nests on ledges, in log cavities, and associated with rootwads, respectively. In the central Casoades, I surveyed >20 Ian of stream in three basins and found 15,3, and 1 nests on ledges, in logs cavities, and associated with rootwads, respectively (Table 3.2). I created sites with 6 nest boxes, 2 ledges, and 2 log cavities. I found slightly more nests I kilometer of stream in the Cascades than in the Coast Range (ANOVA, P = 0.07, Table 3.3) With streams flowing into the Pacific Ocean having intermediate abundances. However, excluding streams where no dippers were seen results in similar abundances in all areas (Appendix F).

Habitat Selection

Habitat characteristics G:19 variables) of nests with known use were not different from nests with unknown use (logistic regression, all P > 0.10). Consequently, I pooled

50

Table 3.2. Total number of American Dipper nest sites (active and inactive), unused sites, and distance surveyed in 4-6th-order streams in the Oregon Coast Range, Cascades, and along the Oregon coast, 1994.

number of nests

number of unused sites

distance surveyed

(km)

Drift Creek

13

6

60.74

streams adjacent to Drift Creek

16

13

42.54

Lobster Creek

7

11

43.92

Lake Creek"

10

10

33.84

Coast Range total

46

40

181.04

Coastal streams"

10

22.08

Cascade streams

16

20.88

Basin

Totals 72 a adjacent to Lobster Creek.

b streams flowing directly into the Pacific Ocean.

224

1

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51

Table 3.3. Mean abundance (sites / linear 10 km of stream) of American Dipper nest sites (active and inactive) and unused nest sites in 4-6th-order streams in the Oregon Coast Range, Cascades, and along the Oregon coast, 1994. Presented are an average of the sites/km for each stream, not a simple average (i.e., not the total number observed / total distance surveyed).

nests

unused sites

distance surveyed (km) x

SE

10

6.1

3.1

1.3

12

3.5

0.7

3.1

1.1

7

6.3

2.7

2.7

1.4

10

3.4

0.5

0.7

39

4.6

1.0

AB

2.2

4

5.5

0.5

B

1.8

6

3.5

1.6

x

SE

x

SE

Drift Creek

3.4

1.7

1.2

0.7

streams adjacent to Drift Creek

3.2

1.0

3.6

Lobster Creek

1.9

1.2

LakeCree~

3.0

1.5

Coast Range total"

2.9

AC

Coastal streams'"

4.9

Cascade streams"

7.3

Basin

number of streams

49 P = 0,0689 Totals a adjacent to Lobster Creek. b values for geographic provinces are least-squared means from the analysis of variance model (n = 49 streams, 224 km surveyed). C column means with the same letters are not different (P ~ 0.08). d streams flowing directly into the Pacific Ocean.

52 all nests for subsequent analyses. Additionally, none of the 506 locations selected at random to evaluate streamside habitat in Drift and Lobster creeks contained a dipper nest or micro- or macro-habitat suitable to hold a dipper nest.

Micro- and macro-habitat at nest sites -

Dipper nests in the Oregon Coast Range

were typically sheltered from the weather ~85% for all nest types) and had a ledge or root on which the nest was placed (100%). Ijudged 24-72% of the nests to be accessible to avian predators but all (100%) were inaccessible to ground predators (Table 3.4). Ledges were wider under nests than at potential, unused nest sites (22 vs. 16 em, Table 3.5), and this was the only micro-habitat feature that distinguished between nests and potential sites on cliff ledges (odds ratio = 1.07,90% confidence interval (CI) on odds ratio

= 1.00 - 1.14, x. 2 =3.5, P =0.06, R 2 =0.12).

However, three macro-habitat

characteristics were different between used and unused sites on cliffs (x.2

=23.1, 3 df, P =

0.0001, R 2 =0.60). Dipper nests were higher above the ground or streambed (2.4 vs. 1.9 m) and farther out over the stream's edge (-0.14 vs. 0.9 m) than potential, unused nest sites (Table 3.5). Within the range of values observed in my study, the likelihood of a dipper using a ledge was 2.7 times greater (odds ratio

=2.7, 90% CI =0.9 -7.6, x.2 =2.4,

P = 0.12) for each l-m increase in elevation from the ground (odds ratio = 1) and only 0.045 times as likely (90% CIon odds ratio

=0.006 - 0.32, x.2 =6.7, P =0.01) for each

meter a ledge was set back from the stream's edge (odds ratio = 1). Cliffs used by dippers also were somewhat longer (20.5 vs. 12.2 m, odds ratio than those not used by dippers (odds ratio

=1.1, x.2 =1.8, P =0.18)

=1), but this may not be meaningful (90% CI

on odds ratio = 0.98 - 1.2). Bridges used by dippers were distinguished from unused bridges by their height, and the angle of the cross member in their support structure (x.2 = 13.2,2 df, P

=0.70).

=0.001, R 2

Bridges with flat undersides did not have ledges to support nests; however, those

with metal or concrete support structures did. Sites on bridges used by dippers were lower (odds ratio

=0.01, 90% CI =0 - 0.44, x. =4.0, P =0.04) than bridges not used by 2

dippers. In addition, the probability of dipper use decreased as bridge cross-member angle (Fig. 3.1) increased to 90° (odds ratio

=0.83,90% CI =0.69 - 1.0, x.2 =2.7, P =

0.10). Overall, bridges with nests had cross members set at sharper angles (X" = 79.4°,


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53

Table 3.4. Proportion of American Dipper nests sheltered from the weather, accessible to avian and ground predators, and with a ledge present in the Oregon Coast Range, 1994.

sheltered from the weather

accessible to avian predators

accessible to ground predators

presence of a ledge

n

%

%

%

%

artificial

9

100

0

0

100

natural

51

90.2

52.9

0

100

unused

42

78.6

52.4

31.0

83.3

nest site

Table 3.5. Micro- and macro-habitat characteristics at sites unoccupied and occupied by American Dipper nests on ledges, bridges, and in log cavities in the Oregon Coast Range, 1994. * indicates variables includedin the logistic regression model.

cliff ledge used" -

bridge unused"

x

SE

n

185.7

129.1

-

log cavitv

used"

-x

x

SE

n

19

40.0

10.0

19 363.0

148.5

1.8

19

16.4*

113.3

39.8

19

cliff height(m)

3.8

0.4

clifflength (m)

20.5*

cliff verticality" (0 from horizontal)

94.6

verticalarea (m')

44.1* 11.6

SE

unused"

SE

n

-x

11 486.5 155.1

11

n

-x

used

unused -

SE

n

36.4

19.5

5

26.6

5.0

7

x

SE

n

Microhabitat ledge length (cm) ledge width (em) ledgeheight(em)

22.1*

2.5

19

17.9

1.7

11

14.8

3.3

11

29.8

3.7

5

27.1

5.8

7

98.1

41.2

19

55.6

8.9

11

47.7

12.6

11

115.8

98.1

8

24.6

4.5

7

19

3.3

0.3

20

3.7

19

12.2*

2.5

20

2.3

19

87.9

4.2

20

19

32.0*

8.5

19 0.2

11

4.6*

0.7

10

1.7

0.2

15

1.5

0.2

6

0.5

11

-2.1

0.6

8

-2.2

0.3

16

-1.9

0.4

7

Macrohabitat

heightbelownest (m) setbackdistanceof the nest

2.4*

0.2

20

1.9*

0.4

20

-0.1*

0.1

20

0.9*

0.3

20

2.7* -2.0

"Ihe equal sample sizes of used and unused nest sites was coincidental. These were not paired analyses. "Ninety degrees is exactly vertical, cliffs 900 slope out over the stream's edge. VI ~


I

55 SE

=5.05, n =10) than those without nests (x =85.6°, SE =2.08, n =8), but this use

pattern was most pronounced on a subset of bridges. Bridges supported by concrete I-beams had cross-members near nests set more acutely (X" under bridges that were not used (X"

=56.7°, SE =2.8, n =3) than

=84.4°, SE =3.1, n =5).

Nests in cavities were in logs smaller than unused logs and without a site for avian predators to land (-,.2 5.7, 2 df, P 0.06, R 2 0.31). I found log cavity nests in

=

=

=

coniferous logs 81.3% (n = 17) of the time. Nests were in somewhat smaller logs (x = 86.9 em diameter, SE

=7.9, n =16 vs. x =120.3 em, SE = 21.6, n =7) and dipper use

was 0.95 - 1.0 (90% CIon odds ratio) times as likely for each one-meter increase in diameter (odds ratio = 0.976, "J! == 2.6, P = 0.10). Dipper nests were less likely to have a suitable landing pad for an avian predator adjacent to the nest (23.5% vs. 57.1 %; odds ratio

=0.184, X =2.3, P =0.13) than unused logs, although there was considerable 2

variability (90% CIon odds ratio = 0.03 - 1.15). I only found 3 nests and 4 potential nest sites in roots or rootwads, thus statistical comparisons were limited (Appendix G).

Geographic variation in nest-site selection -

No micro-habitat variables

distinguished between nests in the Cascades and the Coast Range (P > 0.20); however, three macro-habitat features distinguished nest sites between Ranges (X2 = 16.1,3 df, P = 0.0011, R 2 = 0.51), although these may have little biological significance (Appendix H). Nests on cliff ledges in the Cascades (n = 14) were located on taller cliffs (x = 6.6 m, SE

=1.0 vs. x =3.8 m, SE =0.4; X2 =4.7, P =0.03, odds ratio =1.9,90% CIon odds ratio = 1.2 - 3.0) that were more inclined over the stream (x =105.4°, SE =6.1 vs. x =94.6°, SE =2.4; X2 =3.9, P = 0.05, odds ratio = 1.06, 90%CI = 1.0 - 1.1). Nests in the Cascades were closer to the ground numerically and significantly (x

=2.3 m, SE =0.2 vs. x =2.4,

SE = 0.2; X2 = 3.4, P = 0.07, odds ratio = 0.185) than nests in the Coast Range (odds ratio

= 1, n = 20) although it is unlikely that this is biologically important (9O%CI = 0.04 0.84). Only nests on cliffs had sufficient sample sizes to warrant comparisons.

Riparian zone habitat selection -

Valley form was the only feature

distinguishing between dipper nest sites and random locations (X2

=13,5 df, P = 0.023,

R 2 = 0.083). The stream near dipper nests was more constrained than the available habitat on one (91% vs. 65% of the observations) or both (50% vs. 20%) sides of the

56 stream (Table 3.6). I was 3.5 and 9.6 times more likely to find dippers where the valley walls constrained the stream on one (90% CIon odds ratio = 0.96 - 12.9, 'l = 2.5, P = 0.11) or both sides (90% CIon odds ratio =2.7 - 34.6, 'l unconstrained reaches (odds ratio

=I, Table 3.7).

=8.4, P =0.(037) than in

Dipper nests were located in riparian

areas that were dominated by tree species on both sides of the stream (91% of nest locations vs. 68% of random observations, Table 3.6); however, I was not able to evaluate the importance of riparian forests. I could not analyze variables indicating the presence of a tree-dominated riparian zone, trees along the stream bank, or conifers along the streambank because of inadequate samples in a response category (i.e., 52 nests did not have these features).

Productivity

Reproductive success was based on 48 nesting attempts at 16 nest sites along Drift and Lobster creeks. Daily nest survival was ~.99 (Table 3.8). Nest survival did not differ between Drift and Lobster creeks (P =0.5), among nest types (all P > 0.05), or among nest sites on natural vs. human created structures (p =0.4). Daily nest survival was slightly higher at the artificial nest sites (1.0) than at natural sites along Drift Creek (0.98, P =0.08, Table 3.8). Daily brood survival was >0.99 overall, and was not different among any of the groups (P > 0.16, Table 3.9). The artificial nest sites had no nest or brood failures in 11 attempts. The mean number of chicks fledged per nesting attempt at each site (Appendix 1.1) was not correlated with any of the 36 nest measurements or micro-, macro-, or streamside habitat characteristics (Spearman's rank correlation, all P > 0.05). However, the total number of chicks fledged per site (Appendix 1.2) was correlated with the portion of the stream shaded by the riparian zone vegetation (Spearman's rank correlation, rs = 0.5026, P = 0.0472, n = 16, Fig. 3.2).



57

Table 3.6. Streamside habitat at known American Dipper nest sites and randomly-selected locations in Drift and Lobster creeks in the Oregon Coast Range. 1992-94. * indicates variables included in the logistic regression model. Appendix D contains a more detailed summary.

58

Table 3.7. Variables distinguishing between used and unused nest sites for American Dippers in the Oregon Coast Range, 1992-1994. Wald'l and P values are from logistic regression models fitted with indicator variables for basin and stream order. Each set of variables remained after forward logistic regression eliminated others at a significance level =0.15.


Species variable

parameter estimate

standard error Wald's

x2

P

odds ratio'

lower

upper

American Dipper Intercept"

-4.705

0.973

23.381

0.0001

Basinl"

0.346

0.511

0.460

0.4977

1.41

0.61

3.28

Order4b

0.006

0.612

0.000

0.9923

1.01

0.37

2.75

Order5b

-0.011

0.635

0.000

0.9868

0.99

0.35

2.81

constrained valley form -onebank

1.257

0.789

2.537

0.1112

3.52

0.96

12.87

2.262

0.780

8.420

0.0037

9.61

2.66

34.63

- both banks

a multiplicative likelihood of use given a I-unit increase in the value of a given variable. Odds 1 indicate a greater likelihood of use with an incremental increase in the value of that variable. b Indicator variable included in all models.


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59

Table 3.8 Daily survival of American Dipper nests in Drift and Lobster creeks, among nest substrate types, at sites with natural and human-created substrates, and at natural and experimentally-created sites in Drift Creek in the Oregon Coast Range, 1993-1995.

95% confidence interval on 19-day survival

daily survival Category

n

rate

SE

19-day survival"

lower

upper

Overall

38

0.988

0.000799

0.79

0.658

0.954

Drift Creek

24

0.990

0.001122

0.83

0.677

1.000

Lobster Creek

14

0.983

0.002536

0.72

0.506

1.000

nest box

3

1.000

0.00000o

1.00

1.000

1.000

ledge

17

0.991

0.001599

0.84

0.652

1.000

bridge

12

0.983

0.002865

0.72

0.491

1.000

log cavity

5

0.981

0.008358

0.70

0.338

1.000

1.000

0.00000o

1.00

1.000

1.000

pb

Basin

0.5230

Nest Substrate Type

rootwad Anthropogenic Influences natural sites

15

0.982

0.002662

0.69

0.477

1.000

human created (bridges and created sites)

23

0.991

0.001096

0.84

0.689

1.000

0.4433

Artificial Experiment (Drift Creek only) natural sites

13

0.981

0.003002

0.68

0.459

1.000

created sites

11

1.000

0.00000o

1.00

1.000

1.000

0.0804

Interval survival for the·.19 days of laying/incubation (nest success).

Hensler's (1985) test comparing daily survival of nests between study basins,

nest substrates, anthropogenic sources of nest substrate, and between nest sites we created vs. natural sites (Z-test). C Pairwise comparisons: nest box vs. ledge P = 0.155, nest box vs. bridge P = 0.0806, nest box vs.1og cavity Pi': 0.5115, nest box vs. rootwad P = 0.9999, ledge vs.

bridge P = 0.5034, ledge vs.log cavity P = 0.8837, ledge vs. rootwad P = 0.1554, bridge

vs.log cavity P = 0.8105, bridge vs. rootwad P = 0.0806, log cavity vs. rootwad P =

0.5116. a

b

60

Table 3.9. Daily survival of American Dipper broods prior to fledging in Drift and Lobster creeks, among nest substrate types, at sites with natural and human-ereated substrates, and at natural and experimentally-created sites in Drift Creek in the Oregon Coast Range, 1993-1995.

95% confidence interval

on 25-day survival

daily survival Category

n

rate

SE

25-day

survival"

lower

upper

Overall

35

0.994

0.000008

0.87

0.760

0.997

Drift Creek

22

0.996

0.000009

0.90

0.777

1.000

Lobster Creek

13

0.992

0.000031

0.81

0.620

1.000

nest box

3

1.000

0.00000o

1.00

1.000

1.000

ledge

15

0.994

0.000021

0.84

0.677

1.000

bridge

12

0.996

0.000016

0.90

0.741

1.000

log cavity

4

1.000

0.00000o

1.00

1.000

1.000

0.833

0.023148

-0.09

.51 (95% CIon above correlation coefficients

=-0.50

to 0.37, -0.47 to 0.41, -0.49 to 0.39, and -0.58 to 0.30; respectively).

Censored Deliveries

I could not identify the prey carried by adults during 40% of the deliveries to the nest; however, this proportion of censored, or unseen, deliveries did not change with chick age (F = 0.010, P = 0.9216, r = 0.01, n = 91) or day number (F = 2.575, P = 0.1121, r = -0.17, n = 91). Prey could not be determined often because of an obscured view, the delivering adult flew straight into the nest, or the adult paused only briefly below the nest. The proportion of censored prey was not different between males and females overall (paired t = -0.56, P = 0.59, n

=15 sites, Table 4.5), but this male-female difference

changed with chick age but not with day number (n = 77, F = 5.4, P = 0.02, r = 0.26, Fig. 4.9A; and P = 0.07, r = 0.21, Fig. 4.9B; respectively). Prey delivered to the nest by females was more likely to go unseen early in the brood-rearing period (when chicks ~1O days old, paired t =-2.0, P =0.~5, n = 14, Table 4.5), but this male-female difference did not exist for older (>10 days) chicks (paired t = 0.4, P = 0.70, n = 15,95% CI = -13.6 to 19.6; Table 4.5).

Prey Preference

Adults at four of seven nests foraged from the pan I provided in 44 of 49 trials. Males foraged from the pans at all four nests. Only a single female selected prey twice from a pan. Dippers did not clearly prefer one prey type more than all others. Overall, dippers selected prey in the order: small mayfly, large stonefly or large mayfly, large caddisfly, small caddisfly, small stonefly (Table 4.7), but dipper preference was variable within each combination of prey choices. In addition, their prey selection became more variable as the number of prey items available increased (e.g., combinations 7-10). I rarely provided

98

..-

-a (/.l

eI,) ~

.s

100 60

e 0

40 20 0 -20 -40

= eI,)

-60

~

-80

I

(/.l

eI,)

-a

s

'-'

-e

y = -25.2 + l.4x r=0.26 P=0.022

80

•

80 60

• • • • • •• • •• • I· • • • • • • •

• • • •• • • • • • ••• • ' • • •• • • •

.

(/.l

C,)

••

•

•

100

A

-60

-80

•

-100

0

5

40 20 0 -20 -40

y= a+ bx r = 0.21 P=0.070

• • •• • • •• • • • •• • • • • • •• •I •

•

,•

• • •

15

chick age (days)

20

25

•••• r :• I.

~I·~

I• •• ..~. I

• • • •• •

• •

-100

10

B

•

80 100 120 140 160 180 day number

Figure 4.9. The difference (males - females) in the number of deliveries I hour to American Dipper nests where prey items were not seen (i.e., censored) in relation to nestling ages (A) and day numbers (B) in the Oregon Coast Range (n =77).


I

------------------Table 4.7. Mean rank of selection (e.g., 1 = selected first) and correlation of selection and caloric content for 11 different combinations of prey items offered to American Dippers from pans placed near nests in the Oregon Coast Range, 1994. Multiple trials of the same dipper were pooled prior to the analyses (i.e., n number of individual birds).

=

combination

-x

prey

SE

-

SE

x

5

n=

3

2

I

4

-x

SE

3

5

-

SE

x

3

6

x

SE

5

-x

SE 2

2

7

8

9

10

-x

-

-

-

I

I

I

I

3.17

3.50

x

Cranefly Fish Small mayfly

1.10

0.07

1.96

0.12

Large stonefly Large mayfly Large caddisfly

1.90

0.07

1.21

0.11

2.83

0.18

1.46

0.25

2.12

0.19

2.42

0.30

1.69

2.62

0.13

0.25

1.86

1.90

x

x

1.81

0.81

1.93

0.93

4.21

3.70

3.50

2.88

2.27

0.27

2.29

0.29

3.14

3.00

2.50

2.38

2.35

0.66

2.32

0.68

2.00

2.10

2.75

2.50

3.57

0.43

3.59

0.41

4.29

4.30

4.67

3.75

Small caddisfly

II -

SE

x

2 1.33

0.33

1.67

0.33

5.33

Small stonefly

1.70 .0.32

4.87

0.13

5.50

6.08

po

0.010

0.027

0.069

0.047

0.24

0.13

Spearman's rb

-0.94

-0.12

-0.51

0.048

-0.34

-0.35

0.27

0.42

0.10

-0.012

0.45

Spearman's pb

0.0001

0.76

0.17

0.87

0.41

0.32

0.61

0.49

0.83

0.98

0.55

a b

0.70

Wilcoxon rank sum or Kruskal-Wallis test comparing ranks between or among groups of prey. Spearman's rank correlation coefficient comparing the order of selection and the caloric content. \0 \0

100

fish, but when we did, they were always selected in the first half of the prey items.

Dippers did not select prey based solely on their caloric content. The only correlation between selection and calorie content was negative ® =-0.94, P =0.0001, Table 4.7) indicating dippers first selected the prey with the lowest energy content.

Bias

Observers correctly identified prey items selected by dippers in all cases. Bias (true - estimated length) was 60% of the prey deliveries. Previous work identified caddisfly larvae as a strongly selected or preferred prey item (Mitchell 1968, Sullivan 1973, Ealey 1977). In addition, mayflies also had high forage ratios, indicating selection, during the breeding season in Alberta (Ealey 1977). Most prey was aquatic, although terrestrial, adult insects comprised 5-21% of the prey identified. Similarly, stomachs of six dippers collected during the breeding season in Alberta also contained many terrestrial, adult insects (Ealey 1977), whereas they were absent from 26 and 6 stomachs in winter in Montana (Mitchell 1968) and Washington (Thut 1970). Caddisflies, stoneflies, and mayflies dominated the diet, and these orders appeared to be the most abundant stream macro-invertebrates in riffle or rapid habitat (pers. obs. from kick samples [Merritt and Cummins 1984]). Although fish were not numerically abundant in dipper diets, they represented a substantial energy contribution because of their large size and calorie content. Moreover, crayfish were not previously known to be eaten by dippers but were delivered to nestlings in this study. Dippers returned to the nest with prey that were associated with faster flowing stream habitat. Drunella, lronodes, most Heptageniidae mayflies, Rhyacophila, and

Dicosmoecus cling to the substrate in channel units that are erosional (Merritt and I '

Cummins 1984), such as rapids, riffles, and glides, but the caddisfly Hydatophylax was found in more depositional habitats (e.g., pools, Merritt and Cummins 1984). Foraging dippers used most channel units in proportion to their availability but used riffles less than expected (Chapter 2). However, riffles may be important foraging sites for dippers because 1) dippers used riffles >36% of the time (Chapter 2),2) the prey items we observed dippers bring back to the nest were present in riffles (pers. obs., Merritt and Cummins 1984), and 3) some channel units that were classified as riffles became glides as stream flow decreased throughout the spring and summer.


I


I

103

Species composition of prey fed to nestlings changed throughout the breeding seasons. The higher caloric content of mayflies during the first breeding season was attributable to the large mayfly Drunella. Drunella was delivered more frequently during the first than the second breeding season (pers. obs.) and appeared to be more abundant in the stream during the earlier period as well (pers. obs). Stoneflies were commonly delivered to the nest during the first nesting attempt but were less likely to be delivered during the second attempt. Adult insects were noticeably sparse during the first nesting attempt but abundant during the second attempt. Mitchell (1968) and Ealey (1977) concluded that dippers selected prey according to their relative abundance and relative prey size, dippers selected the larger, more conspicuous members of taxa. Although I did not measure prey availability quantitatively, I noted many apparent changes in abundance and composition of macroinvertebrate prey in the stream (pers. obs.). It appeared that dippers selected and discriminated among prey items, but as prey availability changed, their prey selection patterns changed as well. Future research should quantify this observation. American Dippers could be considered either prey selectors (selecting a low variety of prey species, Thut 1970) or opportunists (high variety, this study, Mitchell 1968, Ealey 1977) based on their prey selection behavior. Thut (1970) and Mitchell (1968) noted examples of focused feeding, such as a stomach nearly full of a single prey or group of prey items. Fecal analyses of Eurasian Dippers have shown strong prey selection in Great Britain, especially when feeding young (Ormerod 198511, Ormerod et al. 1985, Vickery 1991, Shaw 1919) but more opportunistic behavior in Norway (Ormerod et al. 1987). Similarly.dippers in this study often would return to the nest many times carrying the same prey or prey load on a given day; however, the prey load changed throughout the season. Dippers Show strong prey selection (a selector) at smaller spatial and temporal scales; however, as scale increases, dipper foraging behavior becomes more plastic and general. Consequently, studies of prey selection and foraging behavior must be evaluated within the context of their spatial and temporal extent (Miles 1990, Recher 1990).

104 Prey Partitioning

Male and female dippers differed in species composition and abundance of prey delivered to chicks, suggesting sexes selected prey differently and rejecting the prey partitioning null hypothesis. Males delivered more prey and prey that was smaller and had a lower calorie content than that delivered by females. Females brought back larger, calorie-rich foods but made fewer deliveries. This difference in resource use is consistent with a life-history strategy to reduce intersexual competition (hypothesis 1). However, it also may reflect the different parental roles of male and female dippers. Males delivered different prey than females when the chicks were young and the females were brooding, but this was not so when the chicks were older. Foraging strategies changed as chicks aged and male-female differences became indistinguishable. Young chicks 1 chick fledged (#of attempts)

x

SE

-

x

SE

-

x

SE

0.5

10.0

1.0

3.5

0.5

3.5

0.5

8.0

1.8

6.2

1.9

2.8

0.6

2.2

0.7

4.3

7.8

1.9

9.0

3.0

3.3

0.5

3.0

0.7

1.0

6.3

1.0

5.3

1.1

2.0

0.0

1.8

0.3

3.0

-

>1 egg hatched (#of attempts)

0.0

1.0

0.0

Total 16 11.3 1.7 7.6 0.9 6.8 1.1 2.7 2.3 0.3 0.3 "constructed in late 1993 and present only during 1994-1995 breeding seasons.

136

Appendix 1.3 Total reproductive output from American Dipper nests in Drift and Lobster creeks in the Oregon Coast Range, 1993-95. Values are the sum of all reproductive attempts.

eggs laid

eggs hatched

chicks fledged

nests with >1 egg hatched

nests with >1 chick

fledged

Nest substrate type

number

of sites

n8

total

n8

total

n8

total

n8

total

n8

total

nest box

2

7

28

7

23

7

20

7

7

7

7

ledges

5

15

62

13

40

13

31

16

14

13

11

bridges

4

14

60

12

31

13

36

16

13

13

12

log cavities

4

7

28

8

25

8

21

9

8

8

7

rootwads

1

1

J

1

J

1

Q

1

1

1

Q

41

122

43

108

49

43

42

37

Total 16 44 181 8 total number of attempts.

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I I I I I I I I I I I I I

I I I I I I

137

Appendix J. Prey delivered to ligatured nestlings by American Dippers in the Oregon Coast Range, 1994. I chose a subset of nest delivery observations for ligature experiments (e.g., Johnson et al. 1980) to quantify nestling diets. I used a neck ligature for periods not exceeding 30 minutes to restrict chicks from swallowing any prey items. A pipe cleaner or coated copper wire was wrapped snugly around the neck of each chick in the brood. I continued nest delivery observations for 1 delivery per chick before the nest was approached and examined. I then collected prey from the chick's mouths and identified it. This technique was approved by OSU's Animal Care and Use Committee. I successfully collected prey from the mouth of chicks in 3 of 10 ligature attempts (n 7 nests). Caddisflies and mayflies comprised most of the prey species. Attempts failed because the ligatures were applied too loosely (n ~ 4), the adults became disturbed and did not deliver prey (n = 1), or both. The chicks experienced no mortality or injury as a result of these attempts.

=

Source Order

Family

Genera

number collected

Bolus 1 1

unidentified fish Limnephilidae

Dicosmoecus gilvipes

2

Trichoptera

Rhyacophilidae

Rhyacophila

1

Ephemeroptera

Heptageaiidae

Ironodes

6

Heptageaiidae

unidentified

3

Trichoptera Bolus 2

unidentified adult mayflies isopod

10 1

Bolus 3 Trichoptera

Limnephilidae

Dicosmoecus gilvipes

1

138 25

mayflies

A

•

20

4

adult insects

3

•

•

D

•

15

10

5

•••••••• • • • •••• ••••• • •••••••• • • • ••• 1•• '· • • ••••• ·.11

••

o .... ::s

5

0

.d

.....

btl

.......

s:::

CI.l Q)

.....s:::

"'t:J

e

....~

--8 ~

"8::s

2

• ••1. • •• •• • • •

•

4

•

•• • •

•

•

2

••

E

fish

• •

•

• •• • • • •• ••

1

•••• ••• • •• • ,.11•• ••• •••••• ••••

0

•

2

..•: .. • •

1

••

:1•• • •• ••• 1••••••••••

o

•

3

•

•

•• • •••• • • •• • •• •••• •• • ••••

1

3

B

stoneflies

••

•••••• ••• ••••

•• •• • • ••• • I··

•• '. ••••••••••••••••••

o

s:::

14

caddisflies

30

C

12

• • • • • • ••

10

8

6

·

4

•

•••• •••• • •• •• ••

.••!. .. • ••

0

o

5

.

10 15 20 chick age (days)

• •• • • • • ••• • • •• • •

15

•

I.·· . . I .... • · ••··1 • · • ., • .:.. ••• • · . • : • • • .• •.... •

10

.,.

5

• 25

F

•

25

20

.... : ..•· .. ,.. . • ••••

••••••••

2

total number

o o

.. . 5

•

10 15 20 chick age (days)

25

Appendix K.l. The number of mayflies (A), stoneflies (B), caddisflies (C), adult insects (0), fish (E), and total prey items (F) delivered I nestling I hour of observation to

American Dipper nestlings in relation to chick age (n =91) (untransformed data).

I

I

I I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

-I

139 250

mayflies

•

200

•

150

4000

--

-

0

..c:

eo

....s::

.0

~