Most seabirds are constrained to forage near breeding sites when incubating and provisioning offspring but at other times are free to migrate to more favorable foraging habitat. Auklets (Aethia and Ptychoramphus spp., family Alcidae) are considered to be highly mobile during the nonbreeding season, except for one species, the Whiskered Auklet (Aethia pygmaea), which anecdotal evidence indicates remains close to breeding colonies year round. To clarify Whiskered Auklet year-round whereabouts, we deployed light-based archival geolocation “tags” onto breeding adults in 2013 and 2014. To quantify activity on land we used wet–dry logs from the tags and automated digital sound recording of vocalizations at Buldir Island, Aleutian Islands, Alaska, during 2014–2015. Tagged Whiskered Auklets (n = 17) breeding at Buldir remained close to the island all year (mean distance from Buldir 199 km in latitude, 49 km in longitude, which is comparable to measurement error of bird-borne tags recorded in other studies). Audio recordings confirmed presence of vocalizing birds on land from March to October and wet–dry data indicated roosting on land between sunset and sunrise year-round (including more than 14 hr of each 24 hr period in December), except for nocturnal trips to sea during full moons. Our results quantified the extraordinary year-round residency and land roosting of Whiskered Auklets at Buldir. Although it is impossible to generalize from our single study, if typical across this species' range, this places Whiskered Auklets well outside the behavior of all other auks and most seabirds. Year-round residence near breeding sites and land roosting may be behavioral adaptations that interact with the use of near-shore tide rip foraging habitat in a tradeoff of metabolic costs against foraging success.
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Vol. 135 • No. 3