Behavioural factors affecting foraging effort of breeding wandering albatrosses

1. The study examined the behavioural factors that influence variation in f oraging costs of wandering albatrosses (Diomedea exulans Linnaeus) during t wo consecutive years. This was performed by measuring simultaneously foragi ng activities and metabolic rates (W kg(-1)) of breeding birds during the i ncubation 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 a nd flight speed, and equipped with activity recorders to measure landings a nd 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 SID, km) and increased the num ber of landings and take-offs per day by 66% (28.1 +/- 11.4 SD, landings pe r day) compared to 1998. 4. Energy expenditure rates during foraging were significantly higher in 19 99 (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 variatio n in energy expenditure rates of wandering albatrosses, rather than total d istance 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 eff ort 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 x measured BMR, one of the lo west flight cost yet reported for any seabird.