Male vigilance in white-tailed ptarmigan,Lagopus leucurus: mate guarding or predator detection?

Abstract

Male white-tailed ptarmigan accompany their mates 88-92% of sightings before the onset of incubation, and while accompanying their mates, spend 22-30% of their time displaying vigilant behaviour. Two hypotheses to explain the function of male vigilance before onset of incubation were examined in white-tailed ptarmigan. The protection of paternity hypothesis proposes that male vigilance minimizes the threat of cuckoldry, thereby ensuring paternity in a reproductive attempt. Thus, male vigilance should be greatest during periods when females are fertile, and it should increase when the sex ratio is male-biased. The predator detection hypothesis predicts that increasing male vigilance decreases predation risk to their mates and thus may allow females to increase foraging efficiency. The percentage of time males spent in vigilant behaviour during the pre-incubation period did not change significantly with period of female fertility or with the sex ratio of breeding birds. However, males spent significantly more time vigilant in the year when there were more sightings of predators. The proportion of time females spent foraging was positively correlated with the proportion of time their mates were vigilant. Vigilant behaviour before onset of incubation is likely to increase a male's confidence in paternity of that nesting attempt in white-tailed ptarmigan. However, patterns of variation in male vigilance across seasons and between years suggests that this behaviour also functions to allow females to reduce their vigilance for predators, thereby enabling them to forage more effectively before incubation.