Decision-rules for leaping Adélie penguins (Pygoscelis adeliae)

Abstract

Adélie penguins Pygoscelis adeliae were tested as to whether they jump with optimal energy efficiency when moving out of the sea to the land. Adélie penguins risk predation if the jump fails. Swimming penguins usually launch up the side of sea ice to a surface higher than sea level. Analysis of jumping behaviour recorded by a video camera showed that the trajectory of the centre of gravity of the birds during the aerial phase of jumping was parabolic, indicating that the success of landing depends on three parameters at the time of take-off from water: speed, angle and distance from the point of emergence to the ice edge. There was a negative relationship between distance and the take-off angle, suggesting that penguins adjust their take-off angle to the distance from the ice edge. The comparison among hypotheses revealed that penguins did not jump with optimal energy efficiency. Instead, they aimed for the refracted image of the edge of the cliff, which from underwater appears higher than it actually is. This direction-dependent rule seems to be more robust and reliable than the optimal energetic strategy.