Factors affecting nest and brood survival of rock ptarmigan (Lagopus muta) in Interior Alaska

Abstract

Rock ptarmigan (Lagopus muta) are a circumpolar species endemic to high elevations and latitudes of North America and are common throughout Alaska. The r- selected life history of ptarmigan indicates that reproduction and specifically nest and brood survival is the most important component of population growth. However, factors affecting these population parameters have not been studied extensively or intensively, since there have only been three studies done in Alaska. Rock ptarmigan exhibit population fluctuations, which may be caused by changes in reproduction and survival due to predation and weather events. Warming climatic patterns and shifts in the range of their food resources may also be impacting rock ptarmigan populations. Previous research on rock ptarmigan in Alaska was completed five decades ago and methods of assessing their populations have improved. Therefore, a better understanding of factors affecting nest and brood survival is essential for understanding factors limiting population growth, particularly in a rapidly changing environment. In this study, we investigated whether variations in hen age, weather, timing of nest initiation, and nesting habitat affected nest and brood survival across two study sites. We focused this study on previously studied alpine populations of rock ptarmigan at Eagle Summit and Denali Highway sites in Interior Alaska from spring through summer in 2018 and 2019. Hens outfitted with transmitters were monitored weekly to determine the status of their nest or brood. We found canopy cover around the nest had the most effect on nest survival. Survival of nests with a closed canopy was more than five times higher than those with an open canopy at the Eagle Summit site and nearly two times higher at the Denali Highway site. Ptarmigan at Eagle Summit had higher brood survival than ptarmigan at the Denali Highway site. Our modeling indicated that survival of nests and broods was not affected by fluctuations in seasonal weather (e.g., minimum temperature and maximum precipitation). Establishing a basis for understanding temporal and spatial trends in population ecology is essential for effective management in a rapidly changing environment and these findings may improve the management of rock ptarmigan.