Behavioural factors affecting foraging effort of breeding wandering albatrosses
Résumé
1. The study examined the behavioural factors that influence variation in foraging costs of wandering albatrosses ( Diomedea exulans Linnaeus) during two consecutive years. This was performed by measuring simultaneously foraging activities and metabolic rates (W kg –1 ) of breeding birds during the incubation periods of 1998 and 1999. 2. A total of 38 birds (19 in each year) were injected with doubly labelled water, equipped with satellite transmitters to measure foraging distance and flight speed, and equipped with activity recorders to measure landings and take-offs from the water surface. 3. In 1999, birds spent on average 30% more time at sea (11·07 ± 3·53 SD, days), travelled 43% further (5473 ± 2348 SD, km) and increased the number of landings and take-offs per day by 66% (28·1 ± 11·4 SD, landings per day) compared to 1998. 4. Energy expenditure rates during foraging were significantly higher in 1999 (5·3 ± 0·8 SD, W kg –1 , n = 8) compared to 1998 (4·5 ± 0·5 SD, W kg –1 , n = 11). 5. Landing and take-off rates explained the greatest proportion of variation in energy expenditure rates of wandering albatrosses, rather than total distance travelled, flight speed or time in flight. 6. Despite 18% higher foraging costs in 1999, the daily rate of food intake was similar between years, suggesting that energy acquisition per unit effort was lower. 7. The energetic cost of flight for wandering albatrosses was estimated to fall between 3·4 and 5·1 W kg - 1 , or 1·4–2·0 ´ measured BMR, one of the lowest flight cost yet reported for any seabird.