Long-term demography of a white-tailed ptarmigan ( Lagopus leucura) population in Colorado

Animals endemic to alpine habitats have been receiving increasing attention in recent years due to concerns over sensitivities of high elevation systems to climate warming. Long-term datasets are needed to assess trends in populations of alpine endemic species, but such datasets are rare, primarily due to logistical challenges that constrain data collection in these environments. Long-term datasets also provide critical information on impacts of altered climate because they span multiple decades under which climate varies. To accurately forecast or predict the impacts of warming on alpine animals, it is necessary to first understand how they have responded to climate variation in the past. Here, I present a demographic analysis on 43 years (1968-2010) of long-term data for the white-tailed ptarmigan (Lagopus leucura) at an alpine study site in central Colorado. Spring warming was found to advance breeding phenology an average of 10 days over the course of study, and temperature and precipitation were found to be the primary factors affecting timing of nesting. Weather conditions experienced immediately post-hatch were found to have the strongest effects on reproductive success, with seasonal effects being of secondary importance. Both the number of rain days occurring post-hatch and warm and dry seasonal conditions were found to negatively correlate with reproductive success. Reproductive success declined from the mid-1970s through 2008, but the mechanism behind this decline is not entirely understood. Winter precipitation was the weather variable that had the strongest effect on survival of breeding age white-tailed ptarmigan, and survival was reduced during years of low winter cumulative precipitation. Annual rates of population change were greatest during the first decade of study but tended to be lower during subsequent decades. The average annual rate of population change was close to 1, but there was a high amount of variability among years. Several of the weather variables that were found to most strongly impact reproductive success and survival in white-tailed ptarmigan are expected to change in coming decades. Warming summers are a concern given the potential impact on standing snowfields and the potential to reduce brood-rearing habitats. Higher temperatures in the winter may decrease snowpack which was found to negatively affect survival. I discuss the implications for future climate change on white-tailed ptarmigan. Further, I discuss a recently developed method for combining multiple data sources, and explore how these methods can be applied to white-tailed ptarmigan population modeling in the future