Across the North Pacific, dietary-induced stress of breeding rhinoceros auklets increases with high summer Pacific Decadal Oscillation index.

Abstract

**Abstract:** Multi-colony studies of breeding seabirds may provide insights into the mechanistic links between large-scale climate variability and local changes in prey availability. In the North Pacific, the Pacific Decadal Oscillation (PDO) is a dominant climate index, characterized by contrasting effects on sea surface temperature between the western and eastern North Pacific. To examine how inter-annual variability in PDO affects rhinoceros auklets Cerorhinca monocerata across the North Pacific, we measured inter-annual changes in nutritional stress (as reflected in plasma levels of corticosterone) of adults breeding on five colonies (two and three colonies from the western and eastern Pacific, respectively). We also examined concurrent changes in mass and energy content of food loads delivered to chicks. We found that higher summer PDO values were associated with increased corticosterone levels and lower mass and energy contents of the food loads in both the western and eastern North Pacific colonies. Results indicate that higher summer PDO is associated with local changes in forage fish communities leading to reduced availability of energy-rich prey, which, in turn, increases the nutritional stress of breeding birds. We conclude that higher summer PDO index is associated with food-poor conditions for breeding rhinoceros auklets across their reproductive range, and prolonged periods of high summer PDO may be detrimental to the populations of this seabird species. **Authors:** Ui Shimabukuro¹, Akinori Takahashi², Jumpei Okado³, Nobuo Kokubun², Jean-Baptiste Thiebot⁴, Alexis Will⁵, Yutaka Watanuki³, BriAnne Addison⁶, Scott Hatch⁷, J. Mark Hipfner⁸, Leslie Slater⁹, Brie Drummond⁹, Alexander Kitaysky⁵ ¹The Graduate University for Advanced Studies, SOKENDAI, ²The Graduate University for Advanced Studies, SOKENDAI & National Institute of Polar Research, ³Hokkaido University, ⁴National Institute of Polar Research, ⁵University of Alaska Fairbanks, ⁶Deakin University, ⁷Institute for Seabird Research and Conservation, ⁸Pacific Wildlife Research Centre, ⁹U.S. Fish and Wildlife Service