Effect of environmental variability on habitat selection, diet, provisioning behaviour and chick growth in yellow-nosed albatrosses
Résumé
To understand how seabird breeding performance is influenced by environmental variability, it is necessary to compare acquisition processes between contrasted situations, and their consequence for reproduction. We present results on variations in distribution at sea, habitat selection, diet and provisioning behaviour of the yellow-nosed albatross Thalassarche chlororhynchos from Amsterdam Island, and their consequence for chick growth, during 2 years, 1996 and 2001, with contrasted environmental conditions. The position of thermal fronts changed between the 2 years, and the waters around Amsterdam were colder in 2001 than in 1996. Satellite tracking and compositional analysis show that in 2001 birds foraged farther and in colder oceanic waters than in 1996, resulting in poorer foraging success in 2001. During both years, fish dominated the diet, with minor interannual differences: albatrosses fed more on fish (including a higher proportion of the nomeid Cubiceps caeruleus) and less on squid and crustaceans in 1996. Nestling provisioning was half the rate in 2001 compared to 1996, and this difference was mainly due to longer trips in 2001, with a bimodal trip length distribution. Consequently, chick growth differed significantly, with lighter chicks at fledging being produced in 2001 compared to 1996, although wing length was similar between the 2 years. This study indicates that, during unfavourable conditions, yellow-nosed albatrosses are able to increase foraging effort by searching for prey at greater distances from the nest, at the expense of offspring condition.