Diverse patterns of migratory timing, site use, and site fidelity by Alaska-breeding Whimbrels

Authors: Daniel R. Ruthrauff, Christopher M. Harwood, T. Lee Tibbitts, Nils Warnock, and Robert E. Gill Jr.

Year: 2021

Publication: Journal of Field Ornithology

Publication Link: https://onlinelibrary.wiley.com/doi/abs/10.1111/jofo.12365

Keywords: intraspecific variation, migration, migratory timing, Numenius phaeopus, population variation

Abstract: Birds that conduct long-distance migrations exhibit varied patterns of consistency in
migratory timing and site use. Understanding variation in these traits among populations can help uncover
mechanisms driving migratory behaviors and identify potential population threats. Whimbrels (Numenius
phaeopus) are long-distance migratory shorebirds with a Holarctic breeding distribution, and recent studies
have documented population-specific migrations that vary in duration (short to long) and frequency of stops
(none/few to multiple). Factors driving these population-specific differences are unclear. We studied the
migration ecology of Whimbrels breeding in Alaska, USA, using satellite transmitters deployed from 2006 to
2010 and tracked through 2015. Whimbrels moved entirely within the Pacific Americas Flyway, and some
conducted nonstop flights that exceeded seven days across ~ 8700 km. Birds dispersed across numerous sites
throughout the flyway, often using agriculture or aquaculture habitats. Whimbrels generally exhibited fidelity
to breeding and non-breeding sites, but typically only exhibited fidelity to staging sites used prior to long,
nonstop migratory flights. The duration of migration for Whimbrels at more southern non-breeding locations
was longer than for those at more northern non-breeding sites, and birds at more southern sites also
terminated southbound migration later and initiated northbound migration earlier than birds at more
northern sites. Alaska-breeding Whimbrels exhibited greater variation in migratory behaviors than those in
other populations in the species’ range. We attribute this within-population diversity to the extensive breadth
of non-breeding distributions (~ 70° latitude across ~ 8600 km), a range that naturally shaped individual
responses to unequal migratory demands.

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