Red-legged kittiwake feathers link food availability to environmental changes in the Bering Sea

Abstract

The largest breeding population of red-legged kittiwakes Rissa brevirostris has undergone a dramatic decline and subsequent recovery since 1975. The causal mechanism is hypo thesized to be climate-induced food shortages during reproduction, yet little is known about how the basin ecosystem, where breeding red-legged kittiwakes primarily forage, is affected by climate variability. We examined when and under what conditions red-legged kittiwakes experienced food shortages. Head feathers (winter) and first primary feathers (summer; n = 24 and 27 yr, and 194 and 122 individuals, respectively) were collected between 1913 and 2016 on St. George Island and were analyzed for stable isotope signatures of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S). Feathers were also analyzed for corticosterone concentration (fCORT), which indicates a bird's exposure to nutritional stress during feather growth. Summer fCORT concentrations were lower when values of the annual Pacific Decadal Oscillation index were positive. Winter fCORT concentrations and δ15N signatures increased when February sea-ice coverage was extensive. We conclude that, since 1913, warm conditions in the Bering Sea ecosystem have been associated with low nutritional stress in adult red-legged kittiwakes breeding on St. George Island. However, we found no strong evidence for isotopic shifts over this same period. A better understanding of the factors governing the abundance and availability of red-legged kittiwakes' prey is needed to predict the impact of anticipated warming on this species and its foraging habitat.