Abstract

The swimming group size of captive African penguins (Spheniscus demersus) was studied in relation to weather conditions at Ueno Zoo. The occurrence of swimming behaviour did not vary between fair and cloudy conditions. However, the birds synchronized the timing of swimming with each other under cloudy conditions, and swimming group size increased under cloudy conditions. As cloudy weather can reduce the visual ability of penguins in water, and consequently, increase the predation risk, it is suggested that group size covaries with predation risk and this covariation can function as an antipredator response in the wild.