Parental care in seabirds is typically shared by both sexes. However, the contribution of the male and female at different stages may Vary. These differences in ...
Parental care during incubation and chick-rearing in Humboldt penguins, Spheniscus hurnboldti
Sabrina Simone Taylor
Submitted in partial fulfillment of the requirements for the degree of Master of Science
Dalhousie University Halifax, Nova Scotia December 2000
O by Sabrina Simone Taylor, 2000
141
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TABLE OF CONTENTS LIST OF FIGURES ............................................................................................................ LIST OF . TABLES . .................................................... . .
.
ABSTRACT .....................................................................................................................
vi ..
VII
...
viii
ACKNOWLEDGEMENTS .................... . , . . ................................................................ ix GENERAL INTRODUCTION ........................................................................................... 1 Purpose of the Study ................... . . . . ............................................................................ 4
BACKGROUND INFORMATION..................... .......................................................... 6 Humboldt Penguins ....................................................................................................... 6 Anchovy .......................................................................................................................... 7 . -
STUDY SITE AND GENERAL METHODS ................................................................... 9 CHAPTER 1 : SEX DFFERENCES IN PARENTAL CARE AND FORAGING .......... 10 Introduction ................................................................................................................... 10 11 Methods ......................................................................................................................... Observations: Ir~cubationand Feeding ......................................................................1 1 . . Observations: Diving Behaviour ............................................................................... 14 Data analysis ................................................................................................................. 17 Incubation .................................................................................................................. 17 Chick Feeding ........................................................................................................... 18 Dive Analysis ............................................................................................................ 19 Results ................... . . . ... .. .......................................................................................... 20 Colony reproductive success..................................................................................... 20 Incubation ..........,.,................................................................................................. 2 2 Chick Feeding ................................. ......................................................................... 23 Foraging behaviour ................................................................................................... 24 Discussion ................................................................................................................... 2 5
CHAPTER 2: CONSERVATION OF HUMBOLDT PENGUWS ................................. 33 Introduction ................................................................................................................... 33 Methods ......................................................................................................................... 35 Effect of the instruments ........................................................................................... 36 Results ..................................... ,...................................................................................... 36 Foraging - OveralI Patterns ..................................................................................... 36 ........................................................... 39 Effect of the instruments ........................... . . , Discussion ..................................................................................................................... 39 Effect of the instruments ........................................................................................... 43 Conservation and fisheries at Punta San Juan ......................................................... 44 Recommendations ......................... ............................................................................ 46 Future research .......................................................................................................... 47 GENERAL DISCUSSION ...............................................................................................
50
APPENDIX 1....................................................................................................................
53
APPENDIX 2. ..................................- .....--.....--- .................................................... 54 LITERATURE CITED ........................ . . . ........................ . ......... .. ...... ... .............7 2
LIST OF FIGURES Figure 1. An aerial view of Punta San Juan headland. The X marks the location of thc study colony and the line at right angles represents the concrete wall ................. 1 2 Figure 2. Bimodal frequency distribution of diving depths for Humboldt penguins in= 18, during chick-rearing. The first peak represents travelling dives (?--lm ). and the 37 second Peak represents foraging dives ( M mj- ........................................................ Figure 3. Frequency distribution of the number of dives occumng at each hour of the day in Humboldt pengujns during chick-rearing (n= 18). Diving occurs approximatsly five times more frequently between O5:W- I8:OO hrs than between 19:OO - 04:00 hrs. Figure 4. Frequency distribution of foraging trip duration for HumboIdt penguins (n=2 1 ) where the first peak represents day trips and the second peak represents ovemight trips. ........................................................................................................................... 39 Figure 5a. An ovemight trip by a single Humboldt penguin showing two periods of foraging activity during daylight (1230- 18: 16 hrs and 5:32-12:30 hrs) and a period at the surface during darkness ( 18: 16-05:32hrs). ..................................................... 4 1 Figure 5b. A day trip by a single penguin showing foraging activity between 05.16 hrs and I7:33 hrs. ............................................................................................................ 1 2
LIST OF TABLES Table 1. A summary of reproductive success in the study colony. ................................... 2 1 Table 2. Mean incubation time for female (F) and male (M) Humboldt penguins for each of four periods. Femaies spend more time incubating than males. ........................... 23 Table 3. The mean number of regurgitations provided by female (F) and male (M) Humboldt penguins for each of four periods. Fewer regurgitations are provided in the first and last periods, but there is no difference in provisioning between males and females. ............................................................................................................. 23 Table 4. Mean differences in dive depth, duration, maximum depth, maximum duration and time spent foraging for male and female Humboldt penguins. .......................... 25 Table 5. Sex differences in foraging behaviour are variable across penguin species. ...... 28 Table 6. Overnight trips are more cornmon than day trips in Humboldt penguins during chick rearing (n=2 1) .................................................................................................. 40
ABSTRACT Parental care in seabirds is typically shared by both sexes. However, the contribution of the male and female at different stages may Vary. These differences in the relative contribution of the two sexes may influence reproductive success and thus may be important for understanding the management of endangered species. 1 investigated the relative contributions of male and female Humboldt penguins (Spheniscus humboldtt) to parental care dunng incubation and chick rearing by observing the length of incubation shifts (n=ll pairs) and by counting the number of regurgitations provided to chicks by males and females (n=15 pairs). 1 also deterrnined whether there were differences in the arnount of food brought to the young and examined how each sex used the water column by deploying time-depth recorders (n=13 pairs) that collected data on dive depth, duration, time spent foraging, and length of foraging trips for male and female penguins. This information can be used to assess whether there are differences in the amount of food brought to young and whether there are differences in how each sex exploits the water column. Finally, 1 used the data on Humboldt penguin foraging behaviour to make recommendations that could reduce the fisheries-related mortaiity of this endangered penguin. The results of my study showed that fernale Humboldt penguins spent significantly more time incubating than males but that there was no difference in chickrearing behaviour, either in the number of regurgitations provided or in any aspect of foraging behaviour. 1discuss how these results compare to other penguin species and examine the factors that could explain the observed patterns. Humboldt penguin dives were typically short (40.0s I 5.8s) and shallow (1 0.1 m 2.5m) and occurred primarily during daylight hours (93% of al1 dives). Humboldt penguins made two types of foraging trips: ovemight and day trips. Overnight trips included two periods of diving activity and a period at the surface during darkness whereas day trips included activity during daylight only. 1 discuss how these patterns may be related to self-maintenance and chick provisioning or departure time from the colony. Humboldt penguins are considered endangered and are threatened by fisheries, which catch penguins incidentdly in nets. To determine why penguins are caught in nets, 1 related information on incidental catches of penguins in the local small-scale fishery to the data 1 collected on foraging patterns. During a period of high mortality, Humboldt penguins were caught chiefly at night when gillnets were used at the surface, a pattern probably explaineci by the tendency of the penguins to spend the period of darkness on ovemight trips at the surface. ClearIy, penguin by-catch could be reduced by limiting the use of surface nets, especiaily at night. Moreover, because Humboldt penguins most frequently forage between 0-30m during the day, Iimiting the use of nets at these depths dunng the day in areas where penguins forage could further reduce mortality. Males and femdes did not appear to forage differently, therefore recommendations specific to each sex are not warranted. 1 also recommend future research on acoustic alarms and exclusion devices, which may reduce incidental catches of penguins without restricting the fishery.
1 am very gratefd to my supervisors, Marty Leonard and Daryl Boness, for their
patience, support, and their clear, logical thinking. In Peru, I'd like to thank Patricia Majluf for substantial logistical support and hospitality, and Gabriella Battistini, Gina Mon, Milena Roca and Nora Arnpuero for assistance in the field. Several funding agencies provided financial assistance. including the Oregon Zoo. the Wildlife Conservation Society, the Smithsonian Institution George Sisley Fund, the Friends of the National Zoo, The Canadian International Development Agency, the Manomet Centre for Conservation Science, Dalhousie University Faculty of Graduate Studies, the Lett Fund, and NSERC. From the Oregon Zoo, 1 am especially grateful to David Shepherdson for cooperation much beyond anything 1 expected. 1 would like to thank Traci Porter and Alison King for comments on drafts and general moral support, and Mike Schwartz for
HP orientation and conversation. Finally, 1 am indebted to Wade Blanchard for considerable statistical advice, and in particular, for running the randomization test.
GENERAL INTRODUCTION Mating systems in birds are highIy variable and range from social monogamy to polyandry and polygyny. The most common type of avian mating system is social monogamy in which both parents help to raise the young. Lack (1968) proposed that monogarny is the predominant mating system in birds because males and females c m leave the greatest number of offspring when both parents invest in their young. A variety
of studies support this hypothesis (26/29 studies reviewed by Bart and Tomes, 1989) by showing increased growth and survivorship of young when both parents provide care.
Males and females in monogamous mating systems invest in young by building nests, producing Iarger eggs or young, guarding the eggs and young from predators, incubating eggs, and feeding young. These parental care behaviours benefit the young by increasing their survivorship or their future reproductive success (Clutton-Brock and Godfray, 199 1). However, parents also incur fitness costs (Clutton-Brock and Godfray, 199 1 ; reviewed in birds by Nur, l988a) such as increased adult mortality or decreased fecundity in subsequent reproductive bouts. For example, experimentally enIarging broods to increase investment reduces future fecundity in rooks, Corvusfrugilegus (Raskaft, 1985) and survivorship in blue tits, Parus caeruleus (Nur, 198833).
Given the potential costs of care, each parent is expected to minimize expenditure while maximizing fitness and reproductive output, even if it is at the expense of its mate (Clutton-Brock, 199 1; Ridley, 1978; Trivers, 1972; Wright and Cuthill, 1989). This can potentially produce conflict between the sexes. This conflict can range from females
mating with males outside the pair bond (Davies, 1985) to males reducing chick provisioning when food is abundant (Wemham and Bryant. 1998; Wittenberger, 1982). A classic exarnple highlighting conflict between the sexes is a study on dunnocks (Prunella
modularis) (Davies. 1985). Female dunnocks seek copulations from extra-pair males, which augments female reproductive success by increasing clutch size and gaining help feeding the young from the extra male. However, multiple paternity is disadvantageous to the pair-bond male because he invests in young other than his own, thus reducing his reproductive output (Davies, 1985). Despite a socially monogamous system, male and female dunnocks attempt to increase their reproductive success at the expense of their mate.
Although conflict is the usual theoretical framework for studies of parental investment, for groups such as seabirds, there is little evidence for conflict between mates. Seabirds are long-lived colonial breeders who are apparent1y constrained to monogarny by the high energetic costs of foraging for patchily distributed prey (Mock
and Fujioka, 1990;Wooler et al., 1992). Unlike many passerines, a single seabird parent cannot simuItaneously rear chicks and meet its own energetic needs, thus, both parents must invest in the care of their young to prevent complete breeding failure (Oring, 1982; Wooler et al., 1992). Seabirds may also be constrained to monogamy because chicks left unattended for long periods during foraging trips may experience higher levels of mortali ty through harassrnent from other colony members or predati on. Monogarny not only allows both parents to maintain their own body condition, but also to provide protection to their chicks.
Even at the genetic level, where polygamy has been detected for several socially monogamous species, many seabirds appear to be tmly monogamous. There are nurnerous opportunities for extra-pair copulations in colonial seabird species, because of the number and availability of potential partners, and the extended absence of mates during foraging trips (Moller and Birkhead, 1993). However, the existing evidence suggests that although extra-pair copulations are observed, they do not often result in fertilizations (Austin and Parkin, 1996; Hunter et al., 1992; Schwartz et al., 1999). In some seabirds, extra-pair matings seem to precede dissolution of the pair bond and may indicate an unsuccessful reproductive attempt or mate incompatibility (Walsh et al., 2000) rather than individual attempts to increase reproductive success. While conflict
may nonetheless exist in seabirds, behaviours that result in conflict are not likely to be strongly selected if the result is cornplete breeding failure for both parents.
Although foraging conditions in the marine environment may force both male and female seabirds to provide care to reproduce successfully, there are different ways for mates to provide care and those contributions may be sex-specific. Females must lay the eggs, but otherwise both males and females may contribute to the preparation and maintenance of the nest, incubation, and feeding Young. The contribution of each sex to these activities rnay Vary both across and within species. For instance, female Atlantic puffins (Fratercula arctica) spend more time incubating eggs and feed chicks more frequently than males (Creelman and Storey, 1991). while in Wilson's plovers (Charadrius wilsonia cinnamoninus), males spend more time incubating (Thibault and
McNeil, 1995). Within species, the arnount that each sex contributes at the various stages can have important impacts on offspring survival. For exarnple, wandering albaiross (Diomedea exulans) parents with an unbalanced division of incubation duties were more likely to fail than parents that contributed more equally to incubation (Croxall and Ricketts, 1983). Exarnining the relative contributions of males and females to parentai care can provide important information on how a species successfully reproduces because the ability of each mate to provide sufficient care at the appropriate time may affect whether offspring survive.
Penguins may be more energetically constrained than other seabird species because they search for prey by swimming, which is a more costly activity than the foraging flight of other seabirds (Croxdl and Lishman, 1987). The high energetic demands associated with swirnming may mean that penguins are particularly reliant on their mates for timely provisioning of parental care. For endangered species, an understanding of parental care strategies in a constrained environment may clarify the factors important to reproductive success, and thus provide information that is vital for formulating management strategies. One species in particular, the Humboldt penguin (Spheniscushurnboldtï), is endangered yet little is known about its breeding and foraging
ecology.
Purpose of the Study The purpose of my study was to examine sex differences in parental care and foraging in Humboldt penguins. Little is known about either in this species yet both are
important for understanding factors influencing reproductive success. 1 had t wo main goals for this study. The first was to assess how male and female Humboldt penguins contribute to breeding success by studying sex differences In their reproductive behaviours. 1 quantified the time males and females spent incubating eggs and feeding chicks. I also determined whether the foraging behaviour of males and females differed by comparing dive depth, dive duration, foraging time, and foraging trip type of the two sexes. How males and femdes forage may be important in explaining differences in chick provisioning rates.
The second goal of this study was to use the foraging data to identify potential conflicts between penguins and fishenes, and to determine whether fishing activities c m be effective1y modified to prevent incidental catches of penguins. These basic
reproductive and foraging data are important for long-term penguin conservation strategies because they provide critical knowledge about breeding success and resource use.
Below I provide background information on the natural history of Humboldt penguins inciuding a description of anchovy, Engraulis ringens,their main prey item (Hays, 1986). This is followed by a description of the study site and the general methods used in this study. Two chapters follow this information. The first examines the contribution of male and female penguins to incubation and chick-rearing. The second relates foraging patterns of Humboldt penguins to fishing pactises. Finally, a general discussion summarizes both chapters.
BACKGROUND INFORMATION Humboldt Penguins Humboldt penguins are flightless seabirds that breed on land and forage at sea. At my study site, Punta San Juan (15'22' S and 7S022' W), the largest colony in Pem (ca.
4,000 adults), two well-defined breeding peaks occur from April-July and from AugustDecember, with a hiatus for moulting in January-February. Nests may be re-used from year to year and are excavated in guano either as surface nests or burrows. Typically, two sirnilady sized eggs are laid. The incubation and chick rearing penods last about 6 weeks and 10 weeks respectively and both parents incubate and provision the chicks. Penguins
fast during incubation bouts and the resulting weight loss entails an energetic cost (Croxall, 1982). Sexes are slightly dimorphic in size (males are larger) and can be
differentiated by bill Iength and head width (Zavalaga and Paredes, 1997).
Humboldt penguins are distributed dong the Coast of Pem and northem Chile in association with the Humboldt Current and its upwelling system (Hays, 1986), an area considered to be the most productive in the world (Arntz et al., 199 1). El Niiio events occur here when prevailing SE winds cease, upwelling is suspended and an area of anomalously warm water appears around the equator (Barber and Chavez, 1983). El Niiïo events are disastrous to penguins because their major prey (anchovy and sardines, Sardinops s a g a ) die, or become unavailable by descending to deeper waters or migrating to other areas (Arntz et al., 1991). The most recent El Nifio in 1997, the largest
on record, reduced the penguin population at Punta San Juan from 4,000 individuals to about 700.
Penguin populations are probably adapted to periodic crashes in their prey from El Nifio events (Hays 1986), however, other threats also cause population declines. Identified threats to Humboldt penguins include fishing, guano mining, which darnages or eliminates their nesting sites, and their intentional capture for food or for pets by fishermen, who consider them good luck c h m s (Hays, 1984). As a result of population declines, Humboldt penguins were listed as endangered under CITES (Appendix 1. 1991 ) and as threatened by the WCN (1998).
Considering the threats mentioned above, there is Iittle information on Humboldt penguins. Most published studies have dealt with captive animals or basic information such as census data and morphometric features (e.g. Hays, 1984; Hays, 1986; Kojima, 1977; Scholten, 1987; Scholten, 1989a; Zavalaga and Paredes, 1997). For the purposes of conservation, it is difficult to manage a species with no information on basic biology. For this reason, foraging and breeding ecology were targeted as research priorities at the conference on Population and Habitat Viability held on Humboldt penguins in September 1998 (Cheney, 1998).
Anchovy Predator foraging behaviour is often strongly influenced by the behaviour and distribution of prey. Here 1 provide information on anchovy, the main prey item of
Humboldt penguins (Hays, 1986). Anchovy are normalIy found within 80krn of the Coast
in large schools. Schools are mainly neritic descending to 40m during the day and occurring in concentrated groups. At night, the schools rise 5- 10m and disperse (J6hannesson and Vilchez, 1980; Whitehead et al., 1988). Anchovy feed on plankton and are distributed in association with the Humboldt Current. Anchovy also breed throughout the year and have two breeding peaks. The first peak occurs in September, the second occurs in April o r May (Paulik, 197 1). Anchovy mature after a year and attain a length of about l OOmm (Whitehead et al., 1988). Humboldt penguins eat prey, including anchovies, that are 36-270mm in length (Koepcke and Koepcke, 1963 cited in Wilson and Wilson, 1990). The chick-rearing period in Humboldt penguins may coincide with the period in which young anchovy have reached a size that Humboldt penguins commonly take. Thus, both chick-rearing periods in Humboldt penguins may be tirned to occur dunng peak anchovy abundance.
STUDY SITE AND GENERAL METHODS This study was undenaken at Punta San Juan, Peru from May to November 1999. Punta San Juan is a coastal headland that was walled off in the 1950s to protect guanoproducing seabirds including Peruvian boobies (Sila ~wriegata),broun pelicans (Pelecmtus occidettrnlis rltagrts), and guanay cormoran ts (Plzalacrocorax bougairr l-illii 1.
that also nest at this site (Duffy, 1994). Protection from hurnan. vulpine, and canine predators at San Juan eventually resulted in high concentrations of several seabird species, including the largest colony of Humboldt penguins in Peru.
The San Juan peninsula contains a variety of nestinz sites for Humboldt penpinç. Most penguins nest in one large surface nesting colony of 1.100 pairs but there are several srnaller colonies and even individual crevice and burrow nests, that are far from the colonies, where single pairs nest (Schwartz et al., 1999). Care was taken to minimize disturbance to Humboldt penguins because their endangered status is coupled with a tendency to desert surface nests, and because the population was small at the time of the study. I used penguins nesting in crevice and burrow nests for my foraging study. which required that I handle birds, to attach time-depth recorders (TDRs). The instruments 1 deployed were srnaIl and attached in the caudal area to minimize turbulence and drag (Wilson and Culik, 1992). Finally, 1 restricted the period of deployment to two weekh. Individual crevice and burrow nests were checked once every two weeks to determine approximate egg and chick age. Protocol for this study was approved by the Smithsonian Institution, National Zoological Park Institutional Animal Care and Use Committee.
CHAPTER 1: SEX Dllt('E'ERENCESIN PARENTAL CARE AND FORAGING Introduction Despite strong bi-parental care in most seabird species, males and females appear to differ in their contributions to reproduction both across stages of reproduction (courtship, incubation, and chick rearing) and within each stage. Differences in care appear to be related to the need of individual parents to rnaintain body condition while providing for young. For example, male Adelie penguins (Pygoscelis papua) expend
more energy overall than females during incubation (Chappell et al., 1993a). However, females expend more energy than males dunng chick-rearing, presurnably so that the male can recoup rnass lost dunng incubation (Chappell et al., 1993a; Clarke et al., 1998). Although males and females contribute differently during incubation, both parents have to coordinate nest relief because each sex can provide only so rnuch care to the young before it loses excessive body condition and must desert the nest to forage for i tself. Male Adelie penguins desert nests and broods fail (47.5% of al1 egg losses) if females spend too much time foraging and arrive late to relieve the males from incubating (Davis,
1982). SimiIarly, chicks s t m e and nests fail (35.4% of al1 chick losses) if males arrive late to relieve the females (Davis, 1982). Quantifying male and female contributions to raising young may provide insight into how a successful breeding system works because adults that fail to provide care at the appropriate time may fail to raise young.
1 examined the contributions of male and female Humboldt penguins during incubation and chick rearing to document how each sex provides care to the young. Relatively little is known about Humboldt penguin breeding strategies: this is a
preliminary study to document expenditure by males and females during reproduction. At the study colony, 1 compared the lengths of time that males and females incubated and the number of regurgitations that each sex provided. This information gave a measure of how much time each sex devotes to incubation and how much food each parent supplies to the young. For pairs at individual crevice and burrow nests, I used TDRs to assess whether sex differences existed in diving behaviour. 1 examined differences in mean and maximum dive depth and duration, mean foraging time, and trip type dunng the chickrearing penod for each member of a pair to assess how each sex forages. Differences in dive depth and duration may indicate that mdes and femaies are exploiting different depths of the water column and possibly different prey sizes or types (Wienecke and Robertson, 1997). Differences in foraging time or trip type may be indicative of how much food each parent supplies to chicks (Weimerskirch et al., 1997). Potentiai differences in foraging behaviour may affect how each sex provisions the young.
Methods Observations: Incubation and Feeding 1 observed a srnail colony of 23 pairs of Humboldt penguins located at the tip of
the San Juan peninsula (Figure 1) to determine the contribution of males and females to incubation and chick rearing. The colony included two sections: an upper colony, where 1 conducted observations from 2 1 May 1999 to 2 1 August 1999 and a lower colony, which 1 included from 2 1 August to 24 November. Some pairs had already laid eggs or hatched
chicks in the lower colony, so 1 lacked complete data on these pairs (n=5). The upper and lower
Figure 1. An aerial view of Punta San Juan headland. The X marks the location of the study colony and the line at nght angles represents the concrete wall.
colonies together consisted of 120 potential nest sites including 78 surface and 10 burrow nest sites excavated in guano, nine crevice nest sites, and 23 artificiai nest sites.
1 conducted continuous daily observations between 06:OO and 18:Oû from a study
blind Iocated approximately 30m from the edge of the colony. 1 recorded the date and time an individual arrïved at the colony to relieve its mate from incubation and the date and tirne it departed to forage. This allowed calculâtion of the time spent by males and females at the nest during incubation. 1considered an incubation bout to begin when an individual entered the nest and covered the eggs even if the individuai had arrived at the nest site earlier. Similady, 1 considered an incubation bout to end when a penguin left the nest even if it did not leave the colony immediately. Lf 1 did not see a pair switch, then both incubation shifts bounded by the switch were excluded from the analysis. 1 calculated the entire length of the incubation period by recording the dates that eggs were laid and hatched. For one pair of penguins, 1 knew the fiedging date but not when the eggs were laid, so 1used the mean incubation period length for al1 penguins to back calculate the pair's initiation day.
Dunng the chick-rearing period 1 recorded the date and tirne an individual amved to feed chicks or departed on a foraging trip, which allowed me to calculate the Iength of foraging trips. Because parents typically feed chicks immediately after retuming to the colony following a foraging trip, I counted the number of regurgitations a parent provided on the day it returned as a measure of chick provisioning. 1 calculated the penod of chick rearing by recording hatching and fledging dates. For two nests, each containing two
chicks, 1 knew the fledging date but not when the eggs hatched s o 1 used the mean number of days that two chicks were present in nests to assign a hatching date.
Dunng daily observations, 1 also recorded the number of eggs and chicks per pair, the fate of the nests, and the identity of individuais present in the colony. 1 could identify individuals based on the unique spotting patterns on their breast (Scholten, 1989b) and each sex by their behaviour during copulations attempts (Schwartz et al., 1999). Humboldt penguins lay 1-2 eggs (x = 1.8
* 0.54), so in burrow and crevice nests in which
I could not see eggs o r chicks from the blind (n = 4 nests), 1 assumed that the pair had only one egg in order to calculate mortality conservatively. Birds were considered to be paired if they engaged in mutual vocalizations, copulated and were present at the nest together for at least two weeks.
Observations: Diving Behaviour 1 studied Humboldt penguin diving behaviour using Mark7 time-depth recorders
(TDRs; Wildlife Computers, Redmond, WA). Twenty-seven penguins, including 1 3 pairs and one individual, were caught inside single crevice or burrow nests using a sigmoidal hook to catch their leg and pull them to the entrance. Adult penguins were caught to deploy units when their chicks were at least two weeks old (Appendix 1). Tirne-depth recorders wi th VHF radio-transmitters (Advanced Telemetry Systems, Isanti, MI) were glued to the dorsal feathers above the uropygid gland using 5-minute epoxy (Wilson and Culik, 1992). Radio-transmitters were deployed to reIocate penguins in the event that they deserted their nest. The TDRs (MK7s) were two sizes 6.5 X 1.8 X 2.0crn (37g) and
8.5 X 1.1
X 2.0cm (27.5g). and the radio-transmitters were 4.0 X 1.O X 2.5cm (15g).
Males (n=14) and females (n=13) weighed on average 4.48 r 0.20 kg and 3.82 + 0.3 1 kg where a mean weight was caicuIated for each individual using the weight at TDR deptoyment and removal.
The TDRs were programmed to record depth every 7s while a penguin was in contact with salt-water and to record the number of dry readings when the instrument was dry. At the time of instrument deployment, penguins were weighed, measured, and banded with stainless steel flipper bands (Larnboumes, England). When possibIe, the penguins were re-captured after approximately two weeks (n=23) to remove the instruments and to re-weigh the penguins.
To prepare diving data for analysis, 1 downloaded the hexadecimal data files from the TDRs into a PC cornputer and ran two software programs. The first was a zero-offset correction program (ZOC; Wildlife Computers) that corrected for potential drift in the pressure transducer of the TDRs. The second was a dive analysis program (DA; Wildlife Computers) that extracted pre-selected dive parameters (e.g. depth and duration) for dives that exceeded a user-specified depth. 1 considered a dive to occur if the TDR recorded a depth greater than 2m. Otherwise, I considered the penguin to be at the surface to account for both the resolution of the TDRs (0.5rn) and for surface noise from waves spilling over the pressure transducer while the penguin was at the surface.
1 examined penguin diving behaviour at the level of individual dives, diving bouts
and foraging trips. Based on the distribution of diving depths (see Results in the Conservation Chapter), 1defined dives between 2 and 4m as travelling dives and dives greater than 4m as foraging dives (Boness et al., 1994; Chappe11 et al., 1993b; Robinson & Hindell, 1996; Wilson et al., 1989). Diving bouts or petiods of foraging activity were
considered to start if there were a minimum of four consecutive dives of at least 4m followed by a series of deeper dives. Dive bouts were considered to end if the animal remained at the surface for a minimum of 30 min or retumed to land. Foraging trips were defined as any period at sea which lasted a minimum of 30 minutes and included at least one diving bout. A trip ended when the bird retumed to land and remained there for at least 1 hour. Humboldt penguins exhibited two types of foraging trips hereafter referred to as day trips and overnight trips. If a bird went on a foraging trip and retumed on the same calendar day, 1 classified it as a day trip. If a bird left on a foraging trip and retumed on the next calendar day, I classified it trip as an ovemight trip. 1 caiculated the duïation of ovenight and day trips, and calculated the amount of time spent foraging during each trip type. The total time spent foraging consisted of al1 diving bouts in a trip but excluded surface time. 1calculated foraging time for every trip and then took the average time for each penguin to compare foraging time for males and fernales.
Although TDRs were deployed on 27 birds (13 pairs and 1 individual), data from al1 birds were not available for analysis. 1 used the dive records of 7 pairs of penguins to analyze dive parameters including dive depth, duration, maximum depth and maximum duration, and of 9 pairs for trip and bout analysis (Appendix 1). For the remaining pairs,
TDRs failed to work (n=l pair), were not recovered (n=l pair), or the data files had to be modified by the manufacturer (n=4 pairs for dive parameters, n=l pairs for trip and bout analysis). 1 excluded an additional pair from the trip and bout analysis because one member of the pair made a foraging trip approximately four times longer than average (See effect of instruments in Conservation Discussion). To compare the arnount of foraging time associated with overnight and day trips, 1used the dive records of 2 1 penguins. 1 excluded from al1 analyses the one individual whose mate did not have a dive record.
Data analysis For al1 statistical analyses in this thesis, 1 used either SAS Version 6.12 or
SYSTAT Version 8.0.1reported means plus or minus one standard deviation and set significance at a = 0.05. 1used pararnetric tests because the data were normally distributed and independent.
Incubation
I compared sex differences in the length of incubation bouts across time by using a mixed-mode1 repeated measures analysis with nest as the unit of analysis (to account
for paired data) and sex and incubation period as fixed effects. 1 divided incubation into four periods: laying and early, middle, and Iate incubation.
Incubation in Humboldt penguins begins when the first egg is laid, so 1 included the laying penod in this anaiysis. I considered the laying period to begin when the first
egg was laid and to end when the second egg was laid. If the female remained on the nest after laying the last egg, 1 included this time in the laying period. 1 defined the first 1-14 days post-laying as the early period, the next 15-28 days as the middle period, and the last
29-42 days as the late period. If an incubation shift spanned two periods, 1 assigned that shift to the period when incubation began. I used an individual's mean incubation time for each of the four periods in the analysis because penguins occasionally relieved their mate at night and 1 was not able to determine when al1 incubation periods started or ended. I used a mixed-mode1 because 1 lacked data on mean incubation time for one or more penods for some individuals.
In total, I was able to use the incubation data of 1 1 out of 23 pairs of penguins that
Iaid eggs. T h e remaining data were excluded because pairs failed early during incubation (n=6) or because the incubation record was incomplete (n=6). If a pair re-nested, 1 used the mosr complete data frorn one nesting attempt only.
Chick Feeding 1 used the data from 15 pairs of penguins to assess whether there were differences
in the number of regurgitations provided to chicks by males and fernales. 1 andyzed these data in a sirnilar fashion as the incubation data, using a rnixed-mode1 repeated measures analysis, with nests as the unit of analysis, to determine the number of regurgitations provided over time with sex and period as fixed effects. 1 do not have complete data for
al1 individuals because 1 was unable to see every feeding, and because some individuals occasionally returned to the colony at night to feed their chicks. To account for rnissing
data, chick-rearïng was divided into four penods based on the number of days that chicks were present in the nest. I considered day 1-20 (where day 1 was the first day post-hatch) the first period, day 2 1-40 the second period, day 4 1-60 the third period, and day 6 1-80 the fourth penod. The mean number of regurgitations provided d u h g each visit in each period was used in the anaiysis. Any feedings that 1 missed simply resuIted in a less accurate mean for that individual.
1 used a mixed mode1 because 1 had a variable sarnple size for each period.
Specifically, 1 could not calculate means for some periods because of failed nests (n=2), because 1 left the study site before the chicks fledged (n=4), and because I began observations in the lower colony after the chick rearing penod had started (n=2).
Dive Anaiysis
I examined potential sex differences in diving by comparing the mean and maximum dive depth and duration, and mean foraging time of mdes and females by using paired t-tests. 1 considered repeated dives by a single penguin to be nonindependent so a mean value for the entire dive record was caiculated for each measure for each penguin.
1 used a t-test to determine whether there were different arnounts of foraging time
associated with day and ovemight trips, without considering sex. 1 reasoned that if the time spent foraging on day and ovemight trips was significantly different, then it might be useful to examine whether males and females made different proportions of each trip
type. 1 tested for a sex difference in the proportion of day and ovemight trips made by males and females using a randomization test with nest a s the unit of analysis to account for paired data. For each nest, 1caiculated the absolute difference between the proportion of overnight trips made by females and males. 1 then randomly permuted the male and female Iabels within each nest a thousand times to build a reference distribution and assess whether the observed proportion was likely to occur by chance aione.
Some authors have suggested that foraging trip duration is related to the amount of foraging time avaiiable when an individual departs from the colony rather than its sex
(Jansen eî al., 1998). To assess this possibility, 1 classified departures as either morning (O
- 1 159hrs) or afternoon ( 12:00 - 2359hrs). 1 then used a two-way Chi-square
contingency table to assess whether trip type (overnight or day) was associated with morning or afternoon departures.
1 did not perform a repeated mesures analysis of foraging time over the course of
chick development for males and females as 1 did for incubation and chick rearing, because of small sample size, inaccuracy in chick age, and the variability in chick age when the TDR was deployed.
ResuIts Colony reproductive success
From May to November, 23 pairs laid eggs in the colony. Three pairs nested twice, three failed on their first attempt and re-nested, seven failed on their first attempt
and did not re-nest, and ten pairs nested once and succeeded (Table 1). Three females mated with a different male the second time they laid eggs. 1 did not consider this to be a pair re-nesting. Eggs failed because individuals failed to relieve their mates (n=2), intruder males entered the nest (n=2; Taylor et al., in press), fights occurred and eggs
were trampled (n=2), an egg was unviable (n=l), and a newbom chick fell into a neighbouring nest, which caused the adults to stop incubating their own egg and feed the chick. An additional five nests lost eggs because the adults did not incubate after laying. Table 1. A summarv of re~roductivesuccess in the studv colonv. # eggs # chicks Nest M/FID Nesting attempt hatched fledged 1 2 2 72 11/10 68 2/ 1 1 2 2 67 12113 1 2 2 19 819 1 1 1 79 44/43 1 1 1 8 3/4 1 1 1 93 1 12/113 1 2 O 15/23 5/97 1 O O 86 8 1/82 1 O O 84 125/94 1 O O 81 7 1/85 1 O O 19 35/9 1 O O 2 9 11104 1 O O 80 23/22 1 1 O 68 211 2 O O 72 95/10 1 O O 90 1071106 1 2 2 33 53/54 1 1 1 79 44/43 2 1 O 78 8 1/82 2 O O 99 108197 1 2 2 95 1 19/120 1 1 1 80 23/22 2 O O 94 1 15/114 1 1 O 69 62/89 1 2 * 81 7 1/85 2 2 * 67 12/13 2 2 * 89 88/100 1 2 * 91 1 1 111I O 1 3 * * left colony before fledge
Of 12 pairs whose eggs hatched, excluding re-nests, 10 pairs successfully fledged chicks
(Table 1). Five of these nests fledged two chicks each and the other five nests fledged one chick each. During the chick-rearing period, chicks died because an individuai failed to reJieve its mate (n=l), a gull took a chick dunng a fight (n=l), an intruder male entered a nest and killed the chick (n=l), and because an apparently abandoned chick frorn another nest trampled a newly born chick while soliciting food. I do not know the fate of 5 nests that hatched chicks because 1 left the colony before the chicks fledged.
incubation The mean time required for eggs to hatch was 39.9
I1.2
days (n=7 nests).
Typically, the female took the first incubation shift after laying the first egg and then either left the colony before laying the second egg (n=6), or remained on the nest and laid the second egg (n=l). 1 was unable to determine the fernale's laying behaviour for nine nests. One exceptional female laid three eggs.
Significant differences existed in the length of the incubation shifts among periods (Fz6.35,df=3, pcO.00). Adults took shorter incubation shifts during the laying penod than during the early (t=-4.09, d f 4 7 , p
