DIVING BEHAVIOR OF GENTOO PENGUINS, PYGOSCELIS-PAPUA - FACTORS KEEPING DIVE PROFILES IN SHAPE

The foraging ecology of seven Gentoo penguins, Pygoscelis papua, breed ing at Ardley Island, Antarctica was studied using animal-attached dev ices which recorded swimming speed, heading and dive depth. Reconstruc tion of the foraging routes by vectorial analysis of the data indicate d that at no time did the birds forage on the sea bed. Swimming speed was relatively constant at 1.7 m s(-1), but rates of descent and ascen t in the water column during dives increased with increasing maximum d ive depth due to changes in descent and ascent angles, The amount of t ime spent descending and ascending in the water column increased with maximum dive depth as did the duration spent at the point of maximum d epth, Dive profiles were essentially either U-shaped (flat-bottomed di ves), or V-shaped (bounce dives), Development of a model based on simp le probability theory indicated that the optimal dive profile to maxim ize the chances of prey acquisition depends on vertical prey distribut ion and on the visual capabilities of the birds with respect to descen t and ascent angles.