Diving patterns and performance in male and female blue-eyed cormorants Phalacrocorax atriceps at South Georgia
The diving pattems of two male and one female Blue-eyed Cormorants Phalacrocorax atriceps were recorded with continuous-recording time-depth recorders for l0-13 days during the 1990 breeding season. For the female only data on time and depth were retrieved: diving was distributed through the day (including 3lVo at nighQ; mean dive depth was 63 m. Males dived mainly in the afternoon and evening. Their mean dive clepths were 61.4 and 83.9 m; mean dive durations 3.4 and 4.6 min; t ime at maximum depth (bottom time) averaged 28 and 41 % of time submerged; descent time (0.4 and 0.5 min) was shorter than ascent time (1.6 ancl 2.9 min); dive/pause ratios were 0.4 and 0.5 and surface interval was not increased with preceding dive duration. The incubating male making one long dive bout per day, made fewer, longer dives, with less overall bottom time, than thc chick-rearing male, which made at least two bouts per day. Most characteristics of diving in 1990 (a year of avcragc breeding success) were similar to data from 1989 (a year of breeding failure). However, there were morc, shorter dive bouts in 1989 and shallow (travelling) dives were more frequent: both consistent with lower prey availabil ity in 1989 necessitating frequent changes of foraging sites.
Authors: Kato, A., Croxall, J.P., Watanuki, Y., Naito, Y.