Parental investment and the management of an endangered penguin

Abstract

The yellow-eyed penguin, Megadyptes antipodes, is considered one of the most threatened species of penguin in the world. Research has indicated that yellow-eyed penguin parents will reduce their overall investment in offspring to match the available food supply, but they rarely exhibit brood reduction. Increased adult mortality under adverse conditions has led to the suggestion that yellow-eyed penguins incur a cost of reproduction in `poor food' years and that such a cost could be avoided by managers relieving them of the burden of raising one of their two chicks. We examined the effects of artificially reducing brood size in yellow-eyed penguins to determine: (1) how reproductive costs may be expressed, and (2) whether brood reduction has the potential to relieve such costs. Our results indicate that yellow-eyed penguins adjust their level of parental effort according to brood size, at least under favourable conditions of food supply. Moreover, parents of single-chick broods were in better condition and guarded their offspring for longer periods than those raising twins. Nevertheless, we found no significant effects of reducing brood size on adult survival or the frequency with which juveniles were resighted. However, if adult condition is sensitive to the effects of brood size this outcome may have significant implications for their ability to survive post-breeding moult in years when food availability is low. Overall, the study emphasises the value of approaching conservation issues from within a theoretical framework.