Seabird reproductive responses to changing climate and prey communities are mediated by prey packaging

Climatic factors drive changes in forage fish communities and may influence the productivity of piscivorous predators, but specific mechanisms response remain poorly known. Between 1984 2020, we studied rhinoceros auklet Cerorhinca monocerata , a seabird breeding western North Pacific at Teuri Island, Japan. We tested hypothesis that climate-mediated prey-switching affects ‘food packaging’ (i.e. way energy is brought to dependent offspring) success by quantifying relationships between climate, prey density, amount food delivered, growth survival chicks. Prey composition switched 4 times: 1988-1992, 1997-1998, 2013-2014, 2017-2018. All last these switches were associated with (lagged) shifts seawater temperature/Pacific Decadal Oscillation. Rhinoceros auklets multiple each meal-load chicks, numbers inversely correlated size fish. These varied species. The heaviest meal-loads achieved when diets dominated anchovy Engraulis japonicas which occurred during warm phases (1992-2013). Chick production, rates, mass fledgling also highest phases. This study shows climate reproduction shifting manner selected relative community structure abundance.