ORIGINAL PAPER H. Weimerskirch á O. Chastel á Y. Cherel J.-A. Henden á T. Tveraa Nest attendance and foraging movements of northern fulmars rearing chicks at Bjùrnùya Barents Sea Accepted: 25 June 2000 Abstract We studied several aspects of the foraging ecology of fulmars rearing young chicks on Bjùrnùya. To determine precisely the duration of foraging trips during the brooding period, we used an automated logging system that recorded the presence of fulmars ®tted with transponders. We also tracked, with satellite transmitters, four parent fulmars during the brooding period, and two after the chick had been left alone. When brooding the chick, fulmars appeared to alternate very rapidly on the nest, with foraging trips lasting on average 8 h. This period appeared constraining for the birds since parents lost mass. The growth of chicks was dependent on the ability of the female and not the male) to do short foraging trips. At this time birds are foraging at an average distance of 60 km from the colony, with birds concentrating on the shelf around Bjùrnùya. They did not return from one trip to the next to the same foraging area. As the season progressed and the chicks were left alone on the nest, parents increased the dura- tion and maximum range of foraging trips as well as the distance covered. However, they still perform a succes- sion of relatively short foraging trips to the east of the Bjùrnùya shelf but they interspersed these short trips with longer foraging trips. One bird returned twice to the same site along the Norwegian coast 570 km from Bjùrnùya, the other foraged at 580 km in the mid- Barents Sea. Average ¯ight speed including time spent on the water was 28 km/h and reached 70 km/h during bouts of more than 1 h when the bird was probably continuously in ¯ight. Introduction The northern fulmar Fulmarus glacialis) is one of the most common seabirds in the North Atlantic and has spread its range from high arctic sites since the last cen- tury Fisher 1952; Warham 1996). It is an oceanic bird like other members of the order Procellariiformes that are well known to forage at long distances from their breed- ing grounds, even during the breeding season review in Weimerskirch 1998). Yet very little information is avail- able on the foraging zones and foraging range of breeding fulmars. During the incubation period when they alter- nate for periods of 3±5 days Mougin 1967; Hatch 1990a) they have a potential foraging range of several hundreds of kilometres from their nest. During the chick-rearing period, dye-marked birds have been observed at a maxi- mum range of 120 km from the breeding grounds Furness and Todd 1984), but one band recovery sug- gested a potential maximum range for one bird of 466 km Dunnet and Ollason 1982). It is generally suggested that range may be limited during the chick-rearing period because of the high feeding frequency observed in this species Furness and Todd 1984; Hamer and Thompson 1997; Hamer et al. 1997). Like several other species of Procellariiformes, fulmars brood their chick for almost 2 weeks Mougin 1967) before the chick is left alone on the nest and fed by both parents. During the brooding period parents probably alternate very rapidly on the nest Furness and Todd 1984; Hamer et al. 1997). The brooding period is a period of high-energy re- quirement for pelagic seabirds because at this time birds have to fast on the nest to brood and feed the chick that is not thermally emancipated Ricklefs 1983). At this time brooding parents forage at sea for trips of short duration, suggesting that even the most oceanic species have to reduce their foraging range. These restricted foraging zones around the island are probably not as optimal as distant waters that are favoured during incubation, and, moreover, intraspeci®c competition may be high. Accordingly, in several species of Polar Biol 2001) 24: 83±88 Ó Springer-Verlag 2001 H. Weimerskirch &) á Y. Cherel á O. Chastel Centre National de la Recherche Scienti®que, Centre Biologique de ChizeÂ, 79360 Villiers en Bois, France e-mail: henriw@cebc.cnrs.fr Fax: +33-549-096526 T. Tveraa á J.-A Henden Division for Arctic Ecology, Norwegian Institute for Nature Research NINA), The Polar Environmental Centre, 9296 Tromsù, Norway