Proceedings - Teaching and Learning Centre - Simon Fraser ...

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
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