Environmental physiology of the little penguin (Eudyptula minor)

This study investigates the energetic adaptations and constraints of the little penguin in relation to its aquatic lifestyle and examines the possible function of sleep as an energy conserving mechanism. The little penguin had a similar level of standard metabolic rate to other birds. Body temperature was lower than the general avian level and varied with the site of , measurement. Although penguins may be considered cold-adapted due to the thermal consequences of immersion; the results of this study and analysis of published data for other species shows minimal conductance in penguins appears to be relatively high in comparison to other cold-adapted birds due to the shallow insulative layer provided by the penguins waterproof plumage. This limitation is to some extent compensated by a well-developed capacity to alter body insulation. Water represents a severe thermal challenge to the little penguin since the potential for heat loss is two orders of magnitude greater than in air. Heat balance in water was maintained by prevention of excessive heat loss through insulative changes. Limits to the extent of insulation restrict the ability of the little penguin to withstand low water temperatures. Respiratory ventilation in the little penguin was rr.uch less than expected due to a low respiratory frequency and conferred a very high oxygen extraction coefficient. Ventilation during cold exposure rerrained closely associated YJith rPetabolic demands. The high gas exchange efficiency in the little penguin correlates well with its short aerobic diving patterns. Heat exposure resulted in large increases in ventilation and the limited capacity of little penguins to withstand heat exposure is in part explained by low tolerance to changes in. acid-base status. The metabolic response to wind in the little penguin varied with temperature. At thermoneutrality increased convective heat loss with wind was compensated by an increase in body insulation. During cold exposure body and plumage insulation had attained maximal values whereupon increased windspeed resulted in a linear increase in metabolic heat production. The dense, overlapping feathers of the little penguin, however, provide an effective resistance to increased heat loss associated with windspeed. The primary effect of wind upon partitional insulation at neutral and cold temperatures was a decrease in the insulation provided by the thermal boundary layer. Little penguins showed similar electrophysiological correlates of sleep to other birds and exhibited polyphasic sleep patterns. This study showed that the amount of sleep increased at night due to increased frequency of sleep periods and decreased during cold exposure due to a reduction in the length of sleep periods. Sleep was associated with decreased metabolic rate compared to values in quiet wakefulness. This decrease, however, represented only a marginal reduction in daily energy costs