Energetic Requirements for Growth of the Jackass Penguin

Abstract

Energetic requirements for growth of the jackass penguin (Sphenisaa demersus) were studied by hand-rearing captive chicks, and by observing growth rates, feeding rates and meal sizes in the field. Daily gain in mass was highest in the period of linear growth (23-55 days). Daily relative growth decreased with age. Food intake and guano production increased from 20-40 days and thereafter remained constant. Relative food intake decreased with age. Digestive efficiency increased with age, and energetic content of guano decreased with age. Chicks in the field grew at a slower rate than the hand-reared birds and were estimated to have consumed approximately half as much food by time of fledging. Feeding of chicks in the field occurred mainly in the afternoon and daily food intake increased with age. It is possible that the slower growth rates in the field may be due to the necessity for parents to guard chicks from predators, after the onset of the chicks' full thermoregulatory abilities.