Do Adélie penguin fledgling weights provide an index of prey availability?

We examine fledgling weights measured over 11 years at Béchervaise Island in relation to two assumed proxies of prey availability: breeding success and foraging trip duration. Concordance between the two proxies was apparent when considering guard stage foraging trip durations but this was not as strong for the crèche foraging trips later in the season. Fledgling weights which are measured at the end of the breeding season were more strongly correlated with later foraging trips than with earlier trips. We interpret these results as an indication of variable resources between the guard and crèche stages of the breeding season. In some seasons, there appeared to be constant levels of resources throughout the breeding season resulting in good breeding success with heavy fledglings or poor breeding success with light fledglings. In other seasons, there was a disparity between breeding success and fledgling weight. For example, low breeding success could occur in a season with heavy fledglings associated with long foraging trips during the guard period and relatively short trips during the crèche period. The concerns raised by Williams and Croxall (1990) that fledgling weight may increase with an associated truncation of the distribution in poor seasons for seabirds with prolonged chick-rearing periods is unfounded for the Béchervaise Island Adélie penguin population. It would be useful to determine the demographic consequences of variable fledgling weights in terms of subsequent chick survival for this population.