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Fraser River Action Plan 3rd Research Workshop The Winter Ecology of Dunlin (Calidris alpina pacifica) in the Fraser River Delta P. Shepherd CWS/NSERC Research Chair in Wildlife Ecology Simon Fraser University Background Bird populations have long been used as indicators of the health of riverine and estuarine ecosystems. Their position in the food chain makes them vulnerable to the effects of contaminant bioaccumulation, and fluctuations in their populations can be a first indication of problems within an ecosystem. As well, high visibility and the ease with which estuarine bird populations can be monitored makes them good indicators of the effects of effluent clean-up efforts on the one hand, and good predictors of the potential effects of further development on the other. The Fraser River delta is the largest estuary on Canada’s Pacific coast and supports the country’s highest densities of waterbirds, shorebirds and raptors in winter, including between 35,000 and 60,000 Dunlin. It is also a key wetland stopover site for many species of migrant birds flying between breeding habitat in Canada, Alaska and Russia and wintering habitat in southern USA and Central and South America. Over one million shorebirds use the Fraser River delta annually, including internationally important populations of Dunlin and Western Sandpipers (Calidris maurii). As with many of the remaining wetlands worldwide, the Fraser River delta is presently experiencing a great deal of pressure due to the rapidly expanding human population around Vancouver and the resulting increases in housing, recreational and industrial development in the area. As well, the river carries effluent from paper mills and agricultural lands throughout the Fraser system out to sea via the delta. Dunlin feed on invertebrates in the sediment and are in turn fed on by many of the species of raptors that winter in the area (Vermeer & Levings, 1977; McEwan & Whitehead, 1984), but we know little about the dynamics of their role in the Fraser River delta ecosystem. Once the ecology of Dunlin in the delta has been studied, mathematical models can be constructed to predict the effects of further human activities on the population, and informed monitoring programs can be generated. The high visibility of these birds in the delta, present from October through April, should in turn make the implementation of such programs relatively simple. Objectives This study is using radio telemetry to investigate habitat use, movements, home ranges, and activity budgets of four segments of the Dunlin population (male and female adults and juveniles) with reference to environmental variables (time of day, tide, weather, season). At the same time, we are investigating prey availability and predator interactions with reference to habitat and environmental variables (time of day, tide, weather, season). All of the above data will be integrated into interactive GIS maps using the Arcview II program. Vermeer’s (in prep) data on diet will also be incorporated to create a data set that can be used to set up a sentinel species program and to make recommendations for the conservation of wintering shorebirds in the Fraser River delta. Results to Date Statistical analysis has not been started yet, but so far some very interesting trends have been noticed. Habitat use appears to be driven by time of day and precipitation to a much greater extent than expected. Due to the nature of winter tidal fluctuations in the delta, a great deal more and a greater diversity of mudflat habitat is available at night than during the day. Since these birds are able to feed at night (Mouritsen, 1994), and since there is less predation at night, it is expected that the Dunlin would choose to forage more at night than during the day, and that they would do so out on the mudflats. The radio-tracking data appears to show that the Dunlin are feeding at night, but that they tend to do so in the adjacent farmers’ fields to a much greater extent than expected. Whenever it is raining, or when the wind is above approximately 15 km/h, Dunlin are found feeding in Page 301
Fraser River Action Plan 3rd Research Workshop the fields rather than on the flats, but generally only at night. Day/night movements (fields mostly only at night and flats mostly only during the day) are probably driven by predation. Dunlin tend only to be susceptible to avian predators when the tide pushes them up close to the dyke. When they are further out on the flats, they can see predators coming and initiate escape flight. Therefore, it makes sense that they should only choose to feed in the fields at night. The only time I saw the majority of the population in the fields during the day was when the wind was severe (over 25 km/h from the SE). Since it rains quite a lot here during the winter, the birds spend a good deal of time feeding in the fields. Fresh water falling on the mudflat tends to drive marine invertebrates further down into the sediment, and perhaps out of reach of Dunlin. But fresh water falling on terrestrial habitats tends to bring invertebrates (especially worms) closer to the surface. It is not yet clear which of these two situations is the driving force behind the birds’ movements, but an experiment has been initiated looking at differences in available invertebrates in terrestrial vs. marine habitats during day vs. night, and with and without precipitation. Conservation Applications It is important to identify all of the habitats used by Dunlin during their life cycle in the delta, and to establish the level and nature of use of each different habitat type. The fact that these birds are feeding in the fields might affect the bioaccumulation of organics, depending on the types of fields the Dunlin use and the fertilization and pest control techniques used by farmers. In order for Dunlin to be useful as a sentinel species for the delta in winter, we need to know how much feeding they’re doing in each habitat type so as to be able to attribute any changes in status to the proper cause. Due to its proximity to Vancouver, farmland in the delta is slowly but surely (and not so slowly in some areas) being converted into housing developments, golf courses, etc. Since Dunlin wintering here appear to require terrestrial as well as marine habitat, further development of farmland must first take this into account. This project will provide information on which habitats (both marine and terrestrial) are important to Dunlin. Reference List McEwen, E.W., and P.M. Whitehead. 1984. Seasonal changes in body weight and composition of Dunlin (Calidris alpina). Can. J. Zool. 62:154-156. Mouritsen, K.N. 1994. Day and night feeding in Dunlins Calidris alpina: choice of habitat, foraging technique and prey. J. Avian Biol. 25:55-62. Vermeer, K., and C.D. Levings. 1977. Populations, biomass and food habits of ducks on the Fraser Delta intertidal areas, British Columbia. Wildfowl 28:49-60. Vermeer, K., R.W. Butler and G.E.J. Smith. (in prep). Diets of Dunlins and Western Sandpipers as related to prey availability. Canadian Wildlife Service Report. Page 302
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PROCEEDINGS 3rd RESEARCH WORKSHOP F
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TABLE OF CONTENTS Participants ....
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Development of a Citizen’s Monito
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Fraser River Action Plan 3rd Resear
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SESSION 1 PULP MILL EFFLUENT ISSUES
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SESSION 4 AGRICULTURAL ISSUES
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SESSION 5 BIOLOGICAL INDICATORS
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