Diving behaviour of female northern rockhopper penguins, Eudyptes chrysocome moseleyi, during the brooding period at Amsterdam Island (Southern Indian Ocean)

The pattern and characteristics of diving in 14 female northern rockhopper penguins, Eudyptes chrysocome moseleyi, were studied at Amsterdam Island (3 7 degrees 50'S; 77 degrees 31'E) during the guard stage, using electronic t ime-depth recorders. Twenty-nine foraging trips (27 daily foraging trips an d two longer trips including one night) with a total of 16 572 dives of gre ater than or equal to 3 m were recorded. Females typically left the colony at dawn and returned in the late afternoon, spending an average of 12 h at sea, during which they performed similar to 550 dives. They were essentiall y inshore foragers (mean estimated foraging range 6 km), and mainly preyed upon the pelagic euphausiid Thysanoessa gregaria, fishes and squid being on ly minor components of the diet. Mean dive depth, dive duration, and post-d ive intervals were 18.4 m (max. depth 109 m), 57 s (max. dive duration 168 s), and 21 s (37% of dive duration), respectively. Descent and ascent rates averaged 1.2 and 1.0 ms(-1) and were, together with dive duration, signifi cantly correlated with dive depth. Birds spent 18% of their total diving ti me in dives reaching 15 to 20 m, and the mean maximum diving efficiency (bo ttom time:dive cycle duration) occurred for dives reaching 15 to 35 m. The most remarkable feature of diving behaviour in northern rockhopper penguins was the high percentage of time spent diving during daily foraging trips ( on average, 69% of their time at sea); this was mainly due to a high dive f requency (similar to 44 dives per hour), which explained the high total ver tical distance travelled during one trip (18 km on average). Diving activit y at night was greatly reduced, suggesting that, as other penguins, E. chry socome moseleyi are essentially diurnal, and locate prey using visual cues.