Factors affecting fledging weight of Adelie penguin (Pygoscelis adeliae) chicks: a modeling study

An individual-based model is developed to examine mechanisms that potential ly underlie the observed constancy in fledging weight (2.8-3.2 kg) of Adeli e (4Pygoscelis adeliae) penguin chicks, in spite of large variability in th e abundance of Antarctic krill (Euphausia superba), the primary food source . The model describes the energetic requirements of the chick. with growth resulting from the difference between assimilated energy and respiration. P arameterizations of these metabolic processes are based upon experimental a nd field observations. Ingestion of Antarctic krill by the chick is depende nt on the frequency of food delivery to the chick by the adults, which is b ased on measured foraging times. The mass, size, and size frequency distrib ution of Antarctic krill fed to the chick are specified using empirical dat a. The energy content of the Ant arctic krill provided to the chick is take n to be constant or allowed to vary with size. The simulations show that fo od availability is most critical in the latter portion of chick development , when growth rates and food demands are high. Low food availability during this time must be compensated by either feeding chicks with larger krill o f higher caloric value or by increased assimilation efficiency. Periods whe n small krill with lower caloric value dominate require more frequent. feed ing of the chicks in order to attain their observed fledging weight. Thus, although the total food energy given to the chick is the main factor determ ining chick growth, the distribution of food availability relative to chick size (i.e., different net growth rates) and food quality are also factors influencing the fledging weight of penguin chicks. The simulations provide insight into the compensating effects of food delivery, food quality, and m etabolic processes that allow Adelie penguin chicks to reach their observed fledging weight in spite of considerable environmental variability in food supply.