Activity pattern of foraging in the wandering albatross: A marine predator with two modes of prey searching

The foraging activity of wandering albatrosses Diomedea exulans was studied with simultaneous use of satellite transmitters, activity recorders and loggers measuring the timing of feeding. On average birds spent 60% of their foraging time in flight, mostly during the day, and 40% on the water, mainly at night. Birds landed on the water on average 27 times per day. During the day prey were located in flight and caught just after landing. At night prey were caught using it 'sit-and-wait' technique. A mean of 3.8 landings were necessary to catch 1 prey item. Two main foraging behaviours were recognised: (1) birds followed long curvilinear search routes over oceanic waters where they landed on water irregularly and (2) birds concentrated their searching in a defined area and exhibited multiple take-offs and landings, changing flight direction regularly over a short period. This behaviour was used in neritic waters, but also in some specific oceanic sectors. It occurred during the day; at night birds tended to be much less active. Although concentrated searching increases the probability of encountering prey in a patchy environment, the energetic costs associated with such a flight pattern are probably much higher than for long distance moving. The evolution of these 2 contrasting behaviours is discussed in terms of the trade-off between rate of prey capture and energy costs of flight. It is suggested that predators switch from moving to area-concentrated searching after finding prey, and from searching to moving when prey capture is low.