Rørvik, K-A., Pedersen, H.C. & Steen, J.B. 1999: An impact of genetic variation and predation on chick survival in willow ptarmigan Lagopus l. lagopus. - Wildl. Biol. 5: 129-135.

The present study investigates the determinants of chick survival in willow ptarmigan Lagopus l. lagopus. Chick survival was negatively associated with genetic relatedness of mates. This may imply that more chicks die when genetic relatedness of mates is high, i.e. low chick heterozygosity at hatching. Hence, newly hatched chicks with low heterozygosity may have reduced viability and, therefore, might suffer higher mortality due to biotic/abiotic conditions. However, there was no association between the proportion of chicks with low heterozygosity and ambient temperature, but a highly significant association with predation pressure was found. Because newly hatched chicks are unable to maintain their body temperature even at normal ambient temperatures and because willow ptarmigan chicks start chirping when they get cold, it is suggested that chicks with low genetic variation may become more exposed to predation. It is proposed that genetic variation significantly affects viability of ptarmigan chicks, but that predation is the proximate cause of death. Consistent with several earlier studies, predation was related both to nesting females and to survival of the chicks. However, the present study extends these findings by suggesting a relationship between predation on one side and genetic constitution on the other, and that predation on nesting females, by reducing genetic variation among chicks at hatching, enhance chick mortality.

Key words: chick survival, genetics, Lagopus lagopus, predation, temperature, willow ptarmigan

Kjell-Arne Rørvik*, Department of Biology, Division of General Genetics, University of Oslo, P.O. Box 1031 Blindern, N-0315 Oslo 3, Norway
Hans Christian Pedersen, Norwegian Institute for Nature Research, Division of Terrestrial Ecology, Tungasletta 2, N-7005 Trondheim, Norway
Johan B. Steen, Department of Biology, Division of General Physiology, University of Oslo, P.O. Box 1051 Blindern, N-0315 Oslo 3, Norway

*Present address: AKVAFORSK, Institute of Aquaculture Research, P.O. Box 5010, N-1432 Ås, Norway - e-mail: kjell-arne.rorvik@akvaforsk.nlh.no

Received 13 June 1997, accepted 5 May 1999

Associate Editor: Peter J. Hudson