The pattern and characteristics of diving of 55 daily foraging trips perfor
med by 16 female southern rockhopper penguins Eudyptes chrysocome filholi w
ere studied in coastal waters of Kerguelen Archipelago during the guard sta
ge. Diving patterns and dive profiles indicated that birds used 2 foraging
behaviours. First, they performed typical pelagic dives, as previously decr
ibed for other penguin species. Second, they also performed series of conse
cutive square-wave dives reaching similar maximum depths, with no deeper di
ves within the series, all criteria which characterized benthic dives. Two
groups of benthic and pelagic dives were subsequently selected to compare t
heir parameters. In agreement with optimization concepts in foraging theory
, rockhopper penguins maximize bottom time (= feeding time) of benthic dive
s through an increase in both descent and ascent rates, thus minimizing tra
nsit time between the sea surface and the bottom. Regardless of dive depth,
bottom time was longer and diving efficiency higher in benthic dives than
in pelagic ones. Penguins were also more active during benthic dives, as in
dicated by higher numbers of depth and light wiggles at the bottom of these
dives. Bathymetry and dive depth indicate that penguins were able to reach
about 80 % of the sea floor surrounding the colony. Abrupt changes in dive
depth within series of benthic dives were identical in height to the thick
ness of lava flows, the main geological features of the landscape, strongly
suggesting that birds followed the bottom topography at a fine scale. Diet
ary analysis showed that rockhopper penguins fed upon benthic prey (a few f
ish and the mysid Mysidetes morbihanensis) and pelagic organisms, including
the major item Euphausia vallentini. There was a positive linear relations
hip between the mass of food brought ashore and an index of the proportion
of benthic dives during the daily trips, thus emphasizing the importance fo
r rockhopper penguins living in a coastal marine environment of feeding on
pelagic migrators trapped at or near the sea floor during the day.