Effects of predation, body condition and temperature on incubation rhythms of white‐tailed ptarmigan Lagopus leucurus

Abstract

The effects of predation risk, body condition of females, and microclimate at the nest site on timing and length of incubation recesses at 30 nests of white‐tailed ptarmigan Lagopus leucurus were examined. Incubation patterns in 1994 (an early year) were also compared to those of 1995, an unusually late spring with low temperatures. Data on incubation schedules were obtained by placing programable temperature data‐loggers in nests and by direct observation of incubating females. Some egg depredation was associated with movements of hens to and from nests, but there were no apparent differences in risk between crepuscular recesses and daytime recesses. Ptarmigan showed high nest attentiveness (>90%) in both years of the study but took significantly more recesses of longer duration in 1995 than in 1994. This suggests that the amount of recess time was affected by body condition of the female which was lower during incubation in 1995. The overall number of recesses per day did not vary according to cover at the nest site; however, females with nests that had no overhead cover did not leave during the warmest part of the day. It is suggested that timing of recesses in this population of ptarmigan is related to microclimate and body condition, rather than being a strategy to avoid predation.