title: Feather corticosterone reveals stress associated with dietary changes in a breeding seabird.
abstract: Changes in climate and anthropogenic pressures might affect the composition and abundance of forage fish in the world's oceans. The junk-food hypothesis posits that dietary shifts that affect the quality (e.g., energy content) of food available to marine predators may impact their physiological state and consequently affect their fitness. Previously, we experimentally validated that deposition of the adrenocortical hormone, corticosterone, in feathers is a sensitive measure of nutritional stress in seabirds. Here, we use this method to examine how changes in diet composition and prey quality affect the nutritional status of free-living rhinoceros auklets (Cerorhinca monocerata). Our study sites included the following: Teuri Is. Japan, Middleton Is. central Gulf of Alaska, and St. Lazaria Is. Southeast Alaska. In 2012 and 2013, we collected "bill loads" delivered by parents to feed their chicks (n = 758) to document dietary changes. We deployed time-depth-temperature recorders on breeding adults (n = 47) to evaluate whether changes in prey coincided with changes in foraging behavior. We measured concentrations of corticosterone in fledgling (n = 71) and adult breeders' (n = 82) feathers to determine how birds were affected by foraging conditions. We found that seasonal changes in diet composition occurred on each colony, adults dove deeper and engaged in longer foraging bouts when capturing larger prey and that chicks had higher concentrations of corticosterone in their feathers when adults brought back smaller and/or lower energy prey. Corticosterone levels in feathers of fledglings (grown during the breeding season) and those in feathers of adult breeders (grown during the postbreeding season) were positively correlated, indicating possible carryover effects. These results suggest that seabirds might experience increased levels of nutritional stress associated with moderate dietary changes and that physiological responses to changes in prey composition should be considered when evaluating the effect of prey quality on marine predators.
authors.affiliation: Department of Biology and Wildlife Institute of Arctic Biology University of Alaska Fairbanks 311 N. Koyukuk Dr. Fairbanks Alaska 99775.
authors.forename: Alexis
authors.initials: A
authors.lastname: Will
authors.affiliation: Graduate School of Fisheries Hokkaido University Minato-cho 3-1-1 Hakodate 041-8611 Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Watanuki
authors.affiliation: National Institute of Polar Research Tachikawa Tokyo 190-8518 Japan.
authors.forename: Dale M
authors.initials: DM
authors.lastname: Kikuchi
authors.affiliation: National Institute of Polar Research Tachikawa Tokyo 190-8518 Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sato
authors.affiliation: Department of Polar Science SOKENDAI Tachikawa Tokyo 190-8518 Japan.
authors.forename: Motohiro
authors.initials: M
authors.lastname: Ito
authors.affiliation: National Oceanic and Atmospheric Administration Ted Stevens Research Institute 17109 Pt. Lena Loop Rd. Juneau Alaska.
authors.forename: Matt
authors.initials: M
authors.lastname: Callahan
authors.affiliation: Faculty of Veterinary Medicine and Hotchkiss Brain Institute University of Calgary HRIC 1B41 3330 Hospital Drive NW Calgary Alberta T2N 4N1 Canada.
authors.forename: Katherine
authors.initials: K
authors.lastname: Wynne-Edwards
authors.affiliation: Institute for Seabird Research and Conservation 12850 Mountain Place Anchorage Alaska 99516.
authors.forename: Scott
authors.initials: S
authors.lastname: Hatch
authors.affiliation: Department of Natural Resource Sciences McGill University Ste Anne de Bellevue PQ H9X 3V9 Montreal Quebec Canada.
authors.forename: Kyle
authors.initials: K
authors.lastname: Elliott
authors.affiliation: Alaska Maritime National Wildlife Refuge United States Fish and Wildlife Service 95 Sterling Hwy Suite 1 Homer Alaska 99603.
authors.forename: Leslie
authors.initials: L
authors.lastname: Slater
authors.affiliation: National Institute of Polar Research Tachikawa Tokyo 190-8518 Japan ; Department of Polar Science SOKENDAI Tachikawa Tokyo 190-8518 Japan.
authors.forename: Akinori
authors.initials: A
authors.lastname: Takahashi
authors.affiliation: Department of Biology and Wildlife Institute of Arctic Biology University of Alaska Fairbanks 311 N. Koyukuk Dr. Fairbanks Alaska 99775.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kitaysky
keywords: Diet composition; foraging behavior; junk‐food hypothesis; nutritional stress; rhinoceros auklet