Population ecology of willow ptarmigan (Lagopus lagopus) in the presence of spatially concentrated harvest

Abstract

Understanding the potential effects of harvest on wildlife populations is fundamental to both theoretical wildlife science and applied wildlife management. The effects of harvest on wildlife populations vary dramatically and depend on the timing and magnitude of harvest, as well as population-specific states and vital rates. Demographic compensation plays a key role in models of wildlife population dynamics and in developing harvest strategies. However, the degree and form of compensation in a given population depends on its particular ecological and life history characteristics, resulting in the need for population-specific assessments of responses to harvest. Ptarmigan (Lagopus spp.) are ecologically important species and are culturally valued for subsistence and recreational hunting throughout the Holarctic. In Alaska, willow ptarmigan (L. lagopus) are among the most commonly harvested small game species, but the population-level effects of harvest are not well understood. Investigating the population level effects of harvest on these populations would aid harvest management and increase general understanding of the ecology of the species. To this end, I studied the population ecology of willow ptarmigan in a region of Alaska with spatially concentrated harvest along access corridors. I investigated: (1) the effect of harvest, season, and demographic group on survival, (2) the effect of harvest on breeding densities, (3) dispersal and seasonal movements patterns in relation to harvest, and (4) temporal and observer effects on ptarmigan survey efforts. I found that survival rates and breeding densities of willow ptarmigan in heavily hunted areas were substantially lower than those in remote sites without hunting. We did not observe seasonal compensatory mortality and the potential for permanent immigration (i.e., breeding/natal dispersal) to compensate for harvest appeared limited. However, seasonal movements away from breeding territories appeared to distribute the effects of harvest more evenly among ptarmigan from accessible and remote areas during winter and early spring. This suggests that the timing of hunting seasons may play a critical role in determining effects on ptarmigan densities in accessible breeding areas, with early autumn (prior to initiation of seasonal movements) harvest likely having the greatest impact. In addition, when examining ptarmigan survey methodology, I found substantial temporal heterogeneity in the availability of ptarmigan for detection during surveys, as well as variation in observer-specific detection rates. This underscores the importance of investigators considering the role of imperfect and heterogeneous detection when designing ptarmigan monitoring strategies to avoid inaccurate conclusions about abundance and trends.