J,Zool.,Lond (1991)225,177-199
Diving patterns and performance in the Antartic blue-eyed shag Phalacrocorax atriceps
J.P.Croxall, Y.Naito.A.Kato, P.Rothery and D.R.Briggs
The pattern and characteristics of diving of two male blue-eyed shags Phlacrocorax atriceps were studied using continuous-recording time-depth recorders, for a total of 15 consecutive days during which the depth, duration, bottom time, ascent and descent rates and surface intervals of 674 dive were recorded. Deep dives (>35m, averages 80-90m, max.116m) were twice as common (64% versus 34%) as shallow dives (<21m and 90% <10m). Deep dives were long (averages 2.7-4.1 min, max. 5.2min) with half the time spent near maximum depth and fast travel speeds (averages 1.0-2.4 ms-1). Sallow dives were short (averages 0.5 min, max 1.3 min), without bottom time and with slow travel speeds (0.1-0.6 ms-1). The time spent at depth and the diet (mainly benthic fish and octopus) is consistent with benthic foraging; the function of shallow dives is uncertain. Male shags forage mainly in the afternoon in 3-5 distinct bouts of diving. Within bouts (and shorter homogeneous sequences of diving) surface intervals are consistently 2-3 times the preceding dive duration; in other shags the reverse is the case. Blue-eyed shag diving depth, duration and pattern is extreme amongst shangs; and the relationship between dive and surface interval suggesta that they may regularly exceed their aerobic dive limit.
BD91-2
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