Ptarmigan in North America: Influence of Life History and Environmental Conditions on Population Persistence.

Abstract

A BSTRACT.—Three ptarmigan species (Willow Ptarmigan Lagopus lagopus, Rock Ptarmigan L. muta, and White-tailed Ptarmigan L. leucura) occupy the tundra habitats of North America. Willow and Rock Ptarmigan inhabit arctic and alpine regions of Canada and Alaska, while Whitetailed Ptarmigan occupy alpine habitats from Alaska and northern Canada south to New Mexico. Ptarmigan populations have relatively short generation times (1.7 to 2.62 years) with an annual fecundity of 0.4 to 2.04 female fledglings/female. In some populations, annual fecundity depends strongly on re-nesting to replace failed first clutches (predation rate usually >50%). We use demographic data from five study sites (38 study-years) to demonstrate that the life history of the North American ptarmigan varies from fast (r-selection/high fecundity) to slow life styles (Kselection/high survival). Willow Ptarmigan, living in sub-arctic and sub-alpine habitats, have a fast life history. Their populations are most strongly influenced by fecundity and survival of juveniles and yearling females. At the other end of the spectrum, Rock Ptarmigan have a slower life history with nearly 40% lower reproductive output, but over 20% higher adult survival rate. Interestingly, White-tailed Ptarmigan show within-species variation from fast to slow lifestyles across their latitudinal range. White-tailed Ptarmigan in the Yukon allocate more effort to reproduction than those in Colorado, but they have lower annual survival, suggesting that environmental factors can lead to life history shifts even within species. In all species, a well-developed external recruitment (rescue) capacity allows ptarmigan populations to persist in stochastic conditions for breeding and survival. The impact of climate change is expected to differ with life history. Slow life style ptarmigan populations are buffered more from climate change influences that impact fecundity but they are more vulnerable to environmental processes that decrease adult survival than the fast life style Willow Ptarmigan. Received 22 June 2011, accepted 27 September 2011. M