Cause of Death in Willow Ptarmigan Lagopus l. lagopus Chicks and the Effect of Intensive, Local Predator Control on Chick Production

Abstract

Population dynamics of willow ptarmigan Lagopus l. lagopus are dominated by varying numbers of successful recruits to the population. One important component that determines this number is the survival of chicks from hatching to fledging at about two weeks of age. We studied the causes of death of chicks and the effects of intensive, local predator control on chick production in two areas of south‐central Norway from 1997–2004. During 1997–2000, 253 chicks were captured and radio‐tagged in a 2,000 ha area in Dalsbygda, Norway. Average survival for all years from hatching to two weeks of age was 33%. Predation accounted potentially for up to 73% of all deaths. Research‐related deaths accounted for 17% of deaths, while 10% died of other natural causes than predation. In no case did disease or lack of food appear to be the ultimate cause of death. The localisation of broods could not be predicted from brood position the previous day and there was no correlation between brood behaviour and chick death.Intensive local predator control was conducted in a 2,000 ha area in Numedal, Norway during 1998–2004. Red fox Vulpes vulpes, marten Martes martes, mink Mustela erminea, raven Corvus c. corax and hooded crow Corvus c. cornix were trapped or shot. Chick production was calculated based on pigmentation of wing feathers from all birds harvested in September. Mean chick production for all years was 3.1 chicks per two adults in the treatment area and 2.4 in an adjacent area without predator control, but the differences were not significant. In our study, therefore, predator control had no measurable effect on chick production or survival.