Vigilance patterns of wintering Eurasian Wigeon: female benefits from male low-cost behaviour
Résumé
Increased vigilance in male animals has been attributed to mate guarding (male investment hypothesis), to secondary sexual characteristics increasing predation risk (male constraint hypothesis) or for the benefit to the female (female benefits hypothesis). We studied Eurasian Wigeon () while they grazed on dry land, a 'risky' foraging situation, at two points during the winter period (pre- and post-pair formation) to assess if their behaviour was more consistent with one of these three hypotheses. Males were always highly vigilant, and vigilance increased markedly in more risky situations (smaller groups, greater distance from water). Mean male vigilance only changed to a minor extent from the pre- to the post-mating periods. Conversely, female vigilance significantly decreased after pairing, and was then significantly lower than that of males. Prior to pairing, males and females had similar rates of vigilance bouts. Overall, our findings suggest that higher vigilance in male Wigeon in this instance is best explained by the female benefits hypothesis. Because the Wigeon were foraging on land and were highly vigilant, even when unpaired, the females could actually benefit from the males' vigilance without males investing more time in vigilance. In such a situation, paired males rely on 'low-cost vigilance' whereby vigilance serves as a safety mechanism while simultaneously benefitting the female.
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