Effects of Hatching Order, Sibling Asymmetries, and Nest Site on Survival Analysis of Jackass Penguin Chicks

Abstract

We used survival analysis to examine the fates of Jackass Penguin (Spheniscus demersus) chicks on Dassen Island, off the west coast of South Africa. There were two distinct phases of chick loss. The first, when chicks were 0-34 days old, involved losses primarily due to burrow collapse, exposure and drowning, and accidental death in the nest. This mortality was influenced strongly by nest-site characteristics. Overall reproductive success was lowest in open nests, intermediate in burrows, and highest in rock nests. The probability of chick death due to flooding was highest for burrows in shell/guano conglomerate, whereas the risk of burrow collapse was highest in sand. Burrows in high-density colonies had a greater likelihood of collapsing after heavy rain than burrows in low-density areas. The second phase occurred 42-90 days after hatch, when losses were almost entirely due to starvation. Comparisons of survival in control and experimental nests with varying degrees of sibling asymmetry indicate that it is the extent of hatching asynchrony that affects the ability of the smaller sibling to compete for food and that will produce sibling differences in the risk of starvation. Chicks in two-chick control nests starved at higher frequencies than chicks in less asynchronous experimental broods.