Effect of brood size on growth in the Chinstrap Penguin: A field experiment

Abstract

In order to determine if the patterns of chick growth and mortality observed in two-chick broods of the Chinstrap Penguin (Pygoscelis antarctica) are affected by the feeding capacity of parents, we performed an experimental brood reduction at hatching by removing one sibling in some broods and comparing the growth and mortality patterns of these single chicks with those of control broods with two chicks. Chicks in reduced broods had longer flippers than those in control broods at 15, 21 and 47 days of age, and longer bills at 15, 21 and 32 days, but no differences in mass were found. Although more control than reduced broods suffered chick mortality, the productivity of control broods was markedly higher. Brood size has significant effects on final chick size in the Chinstrap penguin. Food limitation operated mainly at the end of the guard stage, although its effects were still significant during the crèche stage. Although the effect of brood size on growth may be more marked in last-hatched chicks, it can also be noted in first-hatched chicks. Growth may act as a fine-tuning mechanism to regulate productivity in this species, allowing parents to raise two chicks, but at the cost of slower growth and smaller final size.