Divergence in chick developmental patterns among wedge-tailed shearwater populations

Abstract

Mechanisms of population divergence in seabirds are poorly understood. We evaluated whether divergent patterns of chick development among wedge-tailed shearwater Puffinus pacificus populations are facultative responses to short-term fluctuations in food availability, or fixed colony-specific phenomena potentially associated with differences in local resource availability. Supplementary feeding at Heron Island increased food intake to levels equal to, or greater than, those observed at Lord Howe Island. In supplemented chicks, mass accumulation per gram of food received was inversely related to current body stores, up to a maximum storage level set by body size. Significantly, maximum storage was lower for Heron Island than for Lord Howe Island chicks at equivalent body size. In contrast, relative allocation to skeletal growth did not differ between supplemented and control chicks, was not influenced by body condition and did not increase to levels observed at Lord Howe Island. Overall, the present study showed that supplemented chicks were unable to use short-term increases in food availability to increase relative mass stores or rates of skeletal development, implying that both life-history parameters have some colony-specific components that are divergent between the locations of this study. Our findings add weight to previous studies suggesting that phenotypic plasticity and/or genetic drift due to philopatry cannot fully explain patterns of morphological, behavioural and physiological divergence among these 2 shearwater colonies.