Diving behaviour of humboldt penguins spheniscus humboldti in northern Chile

Abstract

The Humboldt Penguin Spheniscus humboldti is an endangered species whose population is decreasing over its whole distributional range. In support of conservation efforts, systematic studies are being conducted on the ecology and behaviour of these birds at sea. Time-depth recorders were used to investigate the foraging behaviour of Humboldt Penguins at Isla Pan de Azúcar (26°S, 72°W), northern Chile, during the breeding seasons of 1994/95 and 1995/96. A four-channel logger (MK6, Wildlife Telemetry) equipped with speed, depth, temperature and light-intensity sensors was used to obtain information from 20 foraging trips of 12 penguins, amounting to a total of 301 hours of swimming consisting of 11 011 dives. Birds departed from the colony between 06h00 and 09h00 and returned mainly between 15h00 and 23h00. Distance travelled was strongly correlated with total time spent at sea. Maximum dive depth was 53 m around mid-day when light intensity was maximal. At night maximum depth attained was 12 m. Maximum dive depth was positively correlated with dive duration (r = 0.80), as well as with descent and ascent angle (r = 0.78), and descent and ascent rate (r = 0.86). Dives to between 0.5 and 3 m were interpreted as travelling dives and had a mean depth of 1.6 m. All dives deeper than 3 m were regarded as foraging dives with a mean depth of 11.5 m. Mean dive durations during travelling and foraging were 18.4 s and 47.9 s, respectively. Mean swim speed during travelling was 1.7 m.s-1. Overall speed during foraging dives (descent, bottom and ascent) was 1.9 m.s-1.