Spring Body Condition, Fecundity and Survival in Female Willow Ptarmigan

Abstract

1. We examined variation in spring body mass (adjusted for structural size and number of days before clutch initiation) and its relationship with measures of fecundity and survival for populations of female willow ptarmigan at La Perouse Bay, Manitoba (Lagopus lagopus albus Gmelin) and Chilkat Pass, British Colfumbia (Lagopus lagopus alexandrae Grinnell) in northern Canada. 2. Adult and yearling hen ptarmigan showed an increase in body mass during spring at both La Perouse Bay (LPB) and Chilkat Pass (CP). Although hens at LPB had greater body mass than hens at CP there were no differences in patterns of body mass gain attributable to either years, age-classes, or sites. 3. No differences were found in measures of fecundity or survival between yearlings (1 year of age) in good and poor condition at both sites. At CP, adult (2+ years of age) hens in good condition produced heavy chicks, were more likely to be monogamous, and were more likely to return to the study area in subsequent years than hens in poor condition. Hens in good condition at LPB had higher return rates the following year than those in poor condition but showed no differences in fecundity. 4. As measures of fecundity were not related to a hen's spring body condition, hens in poor condition probably invest relatively more in reproduction than those in good condition. Return of yearling hens was not related to their body condition in spring; however, we did observe low return rates of adult hens in poor condition. Thus, we suggest that the 'cost' of reproduction may be cumulative over years for female willow ptarmigan.