Research Group in Mammalian Ecology and Reproduction, University of Cambridge Physiological Laboratory, Downing Street, Cambridge CB2 3EG, England, and Department of Arctic Biology, University of Tromsø, Post Box 635, N-9001 Tromsø, Norway
N. A. Øritsland
Norwegian Polar Research Institute, Post Box 158, 1330 Oslo Lufthavn, Norway
