M.Sc. Candidate Trent University Peterborough, Ontario, Canada
Stopover sites are a network of high quality areas that shorebirds use to rest and refuel during their long-distance migrations. These areas consist of habitats such as coastal estuaries and tidal mudflats that contain high densities of prey for shorebirds. Understanding how shorebirds use stopover site habitats can help researchers identify which areas are essential for shorebirds to complete their life cycle. The purpose of my research is to investigate shorebird movements between stopover habitats during northward and southward migration in the Pacific Flyway. More specifically, I aim to answer the questions i) do shorebirds show strong site fidelity or do they use multiple habitats during migration stopover?, and ii) what habitat characteristics influence shorebird movements among stopover habitats? We used an automated telemetry system to track individual movements of shorebirds during northward and southward migration at two important stopover sites in British Columbia, the Fraser River Estuary and Tofino. We captured shorebirds in mist nets and attached small radio transmitters (nanotags) to the backs of the birds. Signals emitted from the nanotags were detected from stationary towers located throughout both stopover sites. I also collected sediment cores and identified invertebrate taxa to assess prey availability among stopover habitats.
Movement results for Western Sandpipers (Calidris mauri), the most abundant shorebird species in the Pacific Flyway, show stronger site fidelity during northward (spring) migration than during southward (fall) migration. On average, individual Western Sandpipers move less between habitats during stopover in the spring while making their way to their Arctic breeding grounds than during the fall. Further, Western Sandpipers used the two stopover sites differently; the proportion of tagged birds that move at least once between habitats in the Fraser River Estuary stopover is significantly lower in the spring than in the fall, where there was no difference between seasons in Tofino. Prey availability and distribution also varied between stopover sites. Prey densities and diversity are similar among habitats within the Fraser River Estuary but are significantly different among habitats in Tofino. Similar prey distribution in the Fraser River Estuary may help explain why Western Sandpipers are less likely to move between habitats when they are under a time-sensitive migration in the spring. Our findings show that automated telemetry is an effective way to track movements of shorebirds at a local scale which is a critical component in understanding migration ecology of shorebirds.