Behavioural adaptations of the Jackass penguin, Spheniscus demersus to a hot, arid environment

Abstract

Penguins tend to be overinsulated for life on land. A study of the Jackass penguin Spheniscus demersus was undertaken to investigate the behavioural adaptations that enable the species to cope with the exigencies of a hot, terrestrial environment. The Jackass penguin is mainly crepuscular and nocturnal at its breeding stations. The numbers of birds present on land are highest at night and lowest during the day. The majority of birds leaving a breeding colony do so just after dawn. Birds begin to return to the colony during the late afternoon. The frequency of displays is highest at dawn and from dusk to midnight. This activity cycle enables birds not engaged in incubation or chick guarding to avoid conditions promoting heat stress. Birds remaining in the colony during the day employ strategies such as burrow‐nesting, body‐orientation and evaporative cooling to reduce the effects of high insolation. Compared to the ambient, the microclimate of burrows is more constant; relative humidity is higher; air temperatures fluctuate less; and wind effect is negligible. Most important, birds nesting in burrows are protected from direct insolation. Egg and nest‐air temperature in a burrow are relatively constant. Burrows facing east are cooler than those facing west. However this does not influence burrow‐orientation, which is determined by the slope of the ground. Birds exposed to high insolation orientate with their backs to the sun. The lightly feathered areas of the body are shaded.…