An impact of genetic variation and predation on chick survival in willow ptarmigan Lagopus l. lagopus

The present study investigates the determinants of chick survival in willow ptarmigan Lagopus l. lagopus. Chick survival was negatively associated wit h genetic relatedness of mates, This may imply that more chicks die when ge netic relatedness of mates is high, i.e. low chick heterozygosity at hatchi ng. Hence, newly hatched chicks with low heterozygosity may have reduced vi ability and, therefore, might suffer higher mortality due to biotic/abiotic conditions. However, there was no association between the proportion of ch icks with low heterozygosity and ambient temperature, but a highly signific ant association with predation pressure was found. Because newly hatched ch icks are unable to maintain their body temperature even at normal ambient t emperatures and because willow ptarmigan chicks start chirping when they ge t cold, it is suggested that chicks with low genetic variation may become m ore exposed to predation, It is proposed that genetic variation significant ly affects viability of ptarmigan chicks, but that predation is the proxima te cause of death. Consistent with several earlier studies, predation was r elated both to nesting females and to survival of the chicks. However, the present study extends these findings by suggesting a relationship between p redation on one side and genetic constitution on the other, and that predat ion on nesting females, by reducing genetic variation among chicks at hatch ing, enhance chick mortality.