Movements in Adelie penguins foraging for chicks at Ardley Island, Antarctica; circles within spirals, wheels within wheels

摘要

Eighteen Adelie penguins Pygoscelis adeliae tending chicks at Ardley Island (62°13u27S, 58°55u27W), Antarctica during December 1991 and January 1992 were equipped with multiple channel data loggers recording swim heading, speed and dive depth. These parameters were then equated together using vectors to calculate the foraging tracks of the birds at sea as well as depth utilisation. The deepest dive recorded was 97m although most dives terminated within 70m. In accordance with previous studies, descent and ascent speed of diving birds increased with maximum dive depth and absolute time spent for the descent and ascent increased with maximum dive depth. The distance moved to the farthest point from the island was 35km although 70% of all time at sea was spent within 10km of the island (all birds considered together). Consideration of the fine scale features of bird movement indicated that three major patterns were apparent; (i) virtual straight line movement, (ii) a circular or spiralling movement where circles had diameters ranging between 20 and 200m and (iii) extensive movement without any substantial displacement. A travel index (total distance travelled during a specified time divided by the straight line distance covered during this time) showed that the three behaviours had very different values. The frequency of occurrence of particular travel index values followed a logarithmic decay with straight line travel (with indices around 1) accounting for ca. 35% of all movement at sea with greater deviations from a straight line course occurring less often. It is supposed that straight line travel serves displacement, highly localised movement reflects prey pursuit and that the circular or spiralling movement arises from birds seeking out prey using detection systems other than vision.