Presentation Abstract

Long distant migrants timing their arrival on the breeding grounds must make the tradeoff of optimal timing for breeding vs. optimal timing for survival. For many shorebird species, the flyway northward spans thousands of kilometers, and both conditions encountered en route and the priorities of individuals can affect the timing of migration. We used data from spring migration surveys of Western Sandpipers (Calidris mauri) and Pacific Dunlins (Calidris alpina pacifica) along the Pacific Flyway of North America to determine if the timing of their northward movements changed from 1985 to 2016. We examined 5 sites of varying size along the northern portion of the flyway from Washington, British Columbia, and Alaska, and estimated interannual trends in passage timing relative to each site’s distance to the breeding grounds. The peak passage dates at the sites closest to the species’ breeding grounds in Alaska shifted later by 1-2 days over the study period, while date of peak passage at sites further south shifted ~3 days earlier. A post-hoc analysis suggested local temperature also affected passage dates at most sites, with warmer temperatures being related to earlier passage. Discerning patterns of movement by Dunlins at southern sites was complicated by the presence of winter residents. Simulation analyses of sandpiper movement through a stopover site highlighted both length of stay and timing of arrival as important factors shaping peak passage estimates. We suggest Western Sandpipers appear to be arriving earlier at southern sites, and are spending longer at larger stopover sites such as Alaska’s Copper River Delta. Our analysis generates specific predictions for expected behavior on northward migration and we believe may be a useful indicator in other systems where historical count data are available. Key

Session Title

Shorebird Monitoring in the Salish Sea

Keywords

Shore birds, Monitoring, Estuary

Conference Track

SSE7: Monitoring: Species and Habitats

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE7-477

Start Date

4-4-2018 4:15 PM

End Date

4-4-2018 4:30 PM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 4th, 4:15 PM Apr 4th, 4:30 PM

Divergent trends in migration timing of shorebirds along the Pacific flyway

Long distant migrants timing their arrival on the breeding grounds must make the tradeoff of optimal timing for breeding vs. optimal timing for survival. For many shorebird species, the flyway northward spans thousands of kilometers, and both conditions encountered en route and the priorities of individuals can affect the timing of migration. We used data from spring migration surveys of Western Sandpipers (Calidris mauri) and Pacific Dunlins (Calidris alpina pacifica) along the Pacific Flyway of North America to determine if the timing of their northward movements changed from 1985 to 2016. We examined 5 sites of varying size along the northern portion of the flyway from Washington, British Columbia, and Alaska, and estimated interannual trends in passage timing relative to each site’s distance to the breeding grounds. The peak passage dates at the sites closest to the species’ breeding grounds in Alaska shifted later by 1-2 days over the study period, while date of peak passage at sites further south shifted ~3 days earlier. A post-hoc analysis suggested local temperature also affected passage dates at most sites, with warmer temperatures being related to earlier passage. Discerning patterns of movement by Dunlins at southern sites was complicated by the presence of winter residents. Simulation analyses of sandpiper movement through a stopover site highlighted both length of stay and timing of arrival as important factors shaping peak passage estimates. We suggest Western Sandpipers appear to be arriving earlier at southern sites, and are spending longer at larger stopover sites such as Alaska’s Copper River Delta. Our analysis generates specific predictions for expected behavior on northward migration and we believe may be a useful indicator in other systems where historical count data are available. Key