7 - Winter foraging strategies of a diving seabird: impacts on survival and breeding at high latitudes

Long-lived species living at high latitudes typically schedule breeding activities in the spring and summer to coincide with favourable environmental conditions. To achieve this annual deadline, they must survive the winter when food resources are depress ed, energy expenditure is higher, extreme weather is more frequent and daylength is shorter. Across a species? distribution, latitudinal gradients in environmental severity are particularly marked in winter. Fitness is also dependent on intrinsic ability in activities such as food acquisition. Establishing the interplay between extrinsic and intrinsic factors on winter foraging across a species? distribution is critical to understanding population responses to environmental change. Conditions are expect ed to be particularly severe for diurnal marine endotherms, because of the high costs of foraging in cold water, and greatly reduced light levels. Previous work on the European shag Phalacrocorax aristotelis, a diving seabird, in temperate regions has sho wn that daily foraging time increased to a peak of over 90% of daylight during the winter solstice. Thus, it would appear that shags in temperate regions were foraging close to maximum capacity in mid-winter, and a deterioration in conditions at this time may have had a severe impact on survival and future breeding. These findings are at odds with the distribution of the species, which stretches north into Arctic regions where winter conditions are much more severe, in particular with regard to day length and temperature. The study on temperate shags also highlighted low variation across individuals during mid-winter, but greater variation in early spring with those individuals that had a low foraging effort breeding early. This proposal aims to elucidate the interaction between extrinsic and intrinsic effects on winter foraging across a latitudinal gradient of increasing environmental severity, to establish how this species survives and breeds at high latitudes.