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Pre-incubation behaviour of Harlequin ducks (Histrionicus histrionicus) in Labrador : testing the function of male vigilance and aggression Squires, Kelly A.


Male behaviours such as vigilance and aggression are usually assumed to function in paternity assurance during the pre-incubation period. However, the functions of these behaviours may be to protect females from conspecifics and predators during feeding and resting thereby enhancing their ability to form clutches. I studied pre-incubation behaviour in a population of Harlequin Ducks to determine how male vigilance and aggression are related to female foraging, resting and date of clutch initiation. In 2000 and 2001, 217 hours of time-activity data on 12 paired females and 16 paired males were collected on two rivers in central Labrador during the pre-incubation period. Males face greater risk of losing paternity due to mate loss than to extra-pair copulation (EPC) because EPC attempts were rare and did not result in cloacal contact due to female resistance. Most aggression was low-level 'head-nodding' by both members of a pair. Though high-level male aggression was directed at other males, it occurred during feeding and not resting, despite close proximity between resting pairs and unpaired males. High-level aggression by males was likely used to defend feeding areas and not to 'mate guard'. Harlequin Ducks were observed in lake outlets throughout the preincubation period except during spring snow melt when they were observed feeding close to flooded lakeshores. The proportion of time that males were vigilant during feeding bouts was greater when pairs were observed at the lakeshore than in the river outlets (22% versus 5%). Males were more vigilant than females and were vigilant when other males were not within sight. The frequency of male vigilance was unrelated to the female fertile period suggesting no paternity assurance function. Male vigilance and female feeding and resting were not positively correlated and vigilance and aggression were unrelated to date of clutch initiation. Males may use vigilance to detect predators to enhance female survival in 'risky' habitat

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