Diving patterns and processes in epipelagic and benthic foraging sub-Antarctic seabirds

We contrast the depth, duration and pattern of diving in the epipelagic-foraging Gentoo Penguin (Pygoscelis papua) and the benthic-foraging Blue-eyed Shag (Phalacrocorax atriceps). The daily foraging period was 8 hours in both species, but Gentoos spent 50% of this time diving compared to 20% in Shags. Shags had longer surface intervals between dives than Gentoos, with a higher incidence of extended (>15 min) surface intervals. Dive depth was bimodal with deep (>31m) and shallow (<20m) dives accounting for 72% and 24% of time spent diving in Gentoos, and 90% and 9% in Shags. Deep dives averaged 80m in both species, but were more variable in Gentoos (31-158m) than Shags (34-116m). Gentoos made ten times more total dives per hour than Shags and twice as many deep dives per hour. We discuss these differences in relation to foraging strategy and the distribution and type of prey obtained.