J. A. Percy, A. J. Evans, P. G. Wells and S. J. Rolston (Eds.). 2005. The Changing Bay of Fundy: Beyond 400 Years. Proceedings of the 6th Bay of Fundy Workshop, Cornwallis, Nova Scotia, September 29th - October 2nd, 2004. Environment Canada - Atlantic Region, Occasional Report No. 23. Dartmouth, NS and Sackville, NB.
The Changing Bay of Fundy—Beyond 400 Years
FACTORS AFFECTING MOVEMENT OF SEMIPALMATED SANDPIPERS (Calidris pusilla) MIGRATING THROUGH THE UPPER BAY OF FUNDY Ashley J. Sprague,** Tony W. Diamond and Diana J. Hamilton University of New Brunswick, Fredericton, NB.
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[email protected] Introduction The upper Bay of Fundy is a key migratory stopover point for Semipalmated Sandpipers (Calidris pusilla), a small shorebird which breeds in the Arctic and winters in northern South America. One to two million birds—between 40 percent and 75 percent of the world’s population—visit local mudflats annually, the majority from late July to late August (Hicklin 1987; Mawhinney et al. 1993). Many migrating shorebird species tend to concentrate in large numbers on a restricted number of sites, making them very vulnerable to habitat loss (Morrison et al. 1994). The Western Hemisphere Shorebird Reserve Network has designated the Bay of Fundy as a site of critical importance for these birds (Shepherd and Boates 1999). This mass migration also represents a major attraction for New Brunswick and Nova Scotia tourists interested in wildlife. During their stay in the Bay of Fundy, sandpipers nearly double their weight in preparation for migration to their South American wintering grounds by feeding almost exclusively on mud shrimp (Corophium volutator), the most abundant macroinvertebrate on mudflats in the area (Hicklin and Smith 1984). Semipalmated Sandpipers forage on exposed mudflats during low tide and return to communal roost sites to rest during high tide. Throughout their approximately two-week stay in the Bay of Fundy region, it is not clear how these birds select foraging habitat, or whether they stay on a single mudflat or use multiple mudflats. The selection and use of a foraging site should be based on perceived predation risk, food abundance and availability (Lima and Dill 1990; Elchuk and Wiebe 2002). Populations of Peregrine Falcons (Falco peregrinus) and Merlins (Falco columbarius), the main shorebird predators in the Bay of Fundy, have recently increased due to the banning of DDT use in North America and raptor reintroduction programs (Noble and Elliot 1990). This has resulted in increased predation risks for shorebirds in the Bay of Fundy area, and is likely altering the sandpipers’ choice of foraging areas. Historical evidence prior to the raptor increase suggests that individual Semipalmated Sandpipers restricted feeding to single mudflats (P. Hicklin, pers. comm.); however, mudflat use by shorebirds appears to have changed in recent years (Hamilton et al. 2003). This may be related to changes in feeding habitat, as indicated by loss of mud shrimp from some mudflats (Hamilton et al. 2003), the recovery of predator populations in the area, or other factors.
** First Place Student Paper award winner 110
Session Two: Ecology of Seabirds and Shorebirds
Given the crucial importance of the region to this species, and the global population decline of Semipalmated Sandpipers (Morrison et al. 1994), it is critical from a conservation standpoint that we understand factors influencing shorebird movements and habitat use. Such knowledge will also help to predict future responses of shorebirds to human-induced changes in the ecosystem, such as the damming of tidal rivers and the subsequent removal of these barriers. For example, if we find that birds are able to use multiple mudflats, they may be less vulnerable to changes in their habitat than if they remain on one mudflat throughout their stay. This issue is very relevant to New Brunswick as the province is currently debating the removal of the Petitcodiac Causeway in Riverview, which may alter surrounding mudflats. Specific objectives of this project include: 1. Quantify individual shorebird movements around the upper Bay of Fundy using radio-telemetry. 2. Identify factors that contribute to foraging site selection and individual bird movements during the migration stopover. Methods and Preliminary Results Objective 1: Quantifying movements based on radio-tracking individual birds In early August, during the peak migration period, 20 sandpipers each from Shepody Bay and the Minas Basin were captured using pull traps (following the technique of Peter Hicklin, CWS) and fitted with radio transmitters. Healthy birds with low body weights (indicating recent arrival) were selected. Radio transmitters were attached to an area of clipped feathers on the lower back of the birds using a light coating of waterproof epoxy adhesive (Warnock and Warnock 1993). Tagged birds were tracked using a high-winged monoplane with H-style antennas mounted to the plane’s struts (Kenward 1987). Flights followed the coastline along both Shepody Bay and the Minas Basin in attempts to locate all tagged birds. Birds were also tracked from ground at communal roost sites. Once a tagged bird was detected, the GPS location was noted. Of the 19 birds tagged in Johnson’s Mills (Shepody Bay), 60 percent were not detected at any other mudflat. Only 16 percent were located across the Bay foraging on Daniels Flat. In the Minas Basin, more movement was detected with 30 percent of the birds located on one mudflat, while 50 percent were found on three or more different flats. Objective 2: Factors affecting movement and foraging site selection Prey abundance and size distribution were quantified by sampling Corophium on mudflats in the region. Stratified random sampling of sediments (21 samples per mudflat) was carried out along three transects on each of these selected flats in late July and again in mid-August. Sediment samples were sieved through a 0.25-mm sieve (Crewe et al. 2001) and all Corophium were retained and pre111
The Changing Bay of Fundy—Beyond 400 Years
served in ethanol. At a later date, samples will be sorted and measured in the lab, and the number of Corophium/m2 will be determined. This will facilitate accurate assessment of the prey base at each mudflat for birds observed during the study. Predation threats to the sandpipers were assessed through behavioural observations of shorebirds and predators at selected mudflats. Predator observations were conducted at both high and low tide. Predation risk was quantified by recording the number of predators on each mudflat, number of attacks observed, outcome of attack, and response of sandpipers to predators. A two-way ANOVA found more attacks occurred at high tide than low tide (p = 0.02). No significant difference was found between predation rates in Minas Basin and Shepody Bay. The effects of landscape on bird movements will also be assessed. Detailed maps of the area will be used to determine the following metrics: 1) proximity to roost sites to foraging areas, 2) nearest neighbour distance (km) will be measured from the perimeter of one mudflat to the perimeter of the nearest mudflat, and 3) mean patch size will be the mean area (ha) of the individual mudflats. Conclusion The upper Bay of Fundy is both a rich and diverse wildlife habitat and an important ecotourism site for Atlantic Canada. This research will offer the first solid information on shorebird movements during their migration stopover in this area, especially since the recovery of their predators. This new knowledge on foraging site selection and shorebird movements will lead to suggestions on how to best conserve this crucial habitat and ensure that the world’s largest population of Semipalmated Sandpipers will continue to return to the Bay of Fundy for years to come. References Crewe, T. L., D. J. Hamilton, and A. W. Diamond. 2001. Effects of mesh size on sieved samples of Corophium volutator. Estuarine, Coastal and Shelf Science 53: 151–154. Elchuk, C. L. and K. L. Wiebe. 2002. Food and predation risk as factors related to foraging locations of Northern Flickers. Wilson Bulletin 114(3): 349–357. Hamilton, D. J., M. A. Barbeau, and A. W. Diamond. 2003. Shorebirds, snails, and Corophium in the Upper Bay of Fundy: Can we predict where the birds will go? Canadian Journal of Zoology 81: 1358–1366. Hicklin, P. W. 1987. The migration of shorebirds in the Bay of Fundy. Wilson Bulletin 99(4): 540–570. Hicklin, P. W. and P. C. Smith. 1984. Selection of foraging sites and invertebrate prey by migrant Semipalmated Sandpipers, Calidris pusilla (Pallas), in the Minas Basin, Bay of Fundy. Canadian Journal of Zoology 62: 2201–2210. Kenward, R. 1987. Wildlife Radio Tagging. Academic Press, Toronto, ON. Lima, S. L. and L. M. Dill. 1990. Behavioural decisions made under the risk of predation: a review and prospectus. Canadian Journal of Zoology 68: 619–640. 112
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Mawhinney, K., P. W. Hicklin, and J. S. Boates. 1993. A re-evaluation of the numbers of migrant Semipalmated Sandpipers, Calidris pusilla, in the Bay of Fundy during fall migration. Canadian Field Naturalist 107(1): 19–23. Morrison, R. I. G., C. Downes, and B. Collins. 1994. Population trends of shorebirds on fall migration in Eastern Canada 1974-1991. Wilson Bulletin 106: 431–447. Noble, D. G. and J. E. Elliot. 1990. Levels of contaminants in Canadian raptors, 1966 to 1988: Effects and temporal trends. Canadian Field Naturalist 104(2): 222–243. Shepherd, P. C. and J. S. Boates. 1999. Effects of baitworm harvesting on the amphipod Corophium volutator and on the Semipalmated Sandpiper Calidris pusilla. Conservation Biology 13(2): 347– 356. Warnock N. and S. Warnock. 1993. Attachment of radio-transmitters to sandpipers: Review and methods. Wader Group Study Bulletin 70: 28–30.
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