Citizen science photographs indicate different timing and location use of migrating adult and juvenile Whimbrels

Authors: Chance Hines, Laura Duval, Bryan D. Watts, Grant Van Horn, and Eliot Miller

Year: 2023

Publication: Ornithological Applications

Publication Link:

Keywords: citizen science, demography, migratory phenology, population trends, staging, Whimbrel

Abstract: It is imperative to identify factors that influence population trends for declining species, but demographic parameters can be especially challenging
to quantify for birds, such as Whimbrels (Numenius phaeopus), that breed in locations that are logistically difficult to access. At least two disjunct
Whimbrel populations breed in remote and difficult to access northern latitudes but migrate through the heavily populated North American Atlantic
Coast during autumn migration. Here, we capitalize on the Whimbrel migrations through the more populated coastal areas to age Whimbrels in
photographs uploaded to the citizen science website, eBird, to identify the timing and location of juvenile Whimbrels staging for trans-Atlantic migratory
flights. Mean photograph dates for adult migration were synchronous with reported dates for the Mackenzie Delta population that breeds
along the northern coast of Northwest Territories, Canada, and stages in Atlantic Canada and for the Hudson Bay population that stages along the
South Atlantic USA coast. However, the mean dates of juvenile photographs were 29–41 days later than adult dates, depending on the region.
Space use by juveniles along the coast also differed from that reported for adults. Adults primarily depend on Atlantic Canada and the South Atlantic
USA coast during fall migration. The percentage of juveniles was greater outside these two primary staging locations. Region-specific juvenile
photograph dates suggest that juveniles may drift farther south than the majority of adults from their respective populations. The percentage of
juvenile photos collected better predicted the percentage of adult photos 3 years later than 1 and 2 years later which is consistent with Whimbrel’s
delayed reproductive strategy and provides validation for using photographs to obtain age ratios. As photograph uploads become more commonplace,
this and similar analyses may be used to obtain information that would normally be logistically difficult with traditional field methods.

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