Data from: Feather corticosterone reveals stress associated with dietary changes in a breeding seabird

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.气候变化与人为压力可能影响全球海洋中饵料鱼类的群落组成与种群丰度。「垃圾食物假说（Junk-food Hypothesis）」提出：会影响海洋捕食者可获取食物的品质（如能量含量）的饮食结构转变，可能改变其生理状态，进而影响其适合度。此前，我们已通过实验证实：肾上腺皮质激素皮质酮（corticosterone）在羽毛中的沉积量，是海鸟营养应激的灵敏检测指标。本研究利用该方法，探究饮食组成与猎物品质的变化如何影响野生犀角海鹦（*Cerorhinca monocerata*）的营养状态。本研究的采样位点如下：日本天卖岛（Teuri Is.）、阿拉斯加湾中部的米德尔顿岛（Middleton Is.），以及阿拉斯加东南部的圣拉扎里亚岛（St. Lazaria Is.）。2012年与2013年，我们收集了亲鸟投喂雏鸟的「喙载猎物」共758份，以记录其饮食组成的变化。我们在47只繁殖期成鸟身上部署了时间-深度-温度记录仪，以探究猎物资源的变化是否与觅食行为的改变相匹配。我们分别检测了71只雏鸟与82只繁殖成鸟的羽毛皮质酮浓度，以明确觅食环境对海鸟的影响。研究结果显示：各繁殖群落的饮食组成均存在季节性变化；成鸟在捕食体型更大的猎物时，下潜深度更深、觅食持续时间更长；而当成鸟带回体型更小或能量更低的猎物时，雏鸟羽毛中的皮质酮浓度显著升高。繁殖期生长的雏鸟羽毛与繁殖后换羽的成鸟羽毛中的皮质酮水平呈显著正相关，提示存在潜在的携带效应（carryover effects）。上述结果表明，海鸟可能因饮食组成的适度改变而面临更高水平的营养应激；在评估猎物品质对海洋捕食者的影响时，应纳入猎物组成变化引发的生理响应这一考量因素。