Male reproductive tactics in the mallard, Anas platyrhynchos: social and hormonal mechanisms

Abstract.

It has been proposed that pair status is a proximate cue influencing the mating tactics adopted by male waterfowl. Specifically, it is thought that, compared to unpaired males, paired males are more likely to force extra-pair copulations, but are less likely to court females. Currently, it is unclear how social cues interact with physiological mechanisms affecting male mating tactics. Because of its association with both sexual and aggressive behavior, testosterone may be involved in mating tactic decisions, either in association with or independently of social cues. In this study I investigated the influence of testosterone and pair status on courtship and forced copulation behavior in captive male mallards, Anas platyrhynchos, by staging introduction trials between a male and female that were not paired to each other. Here, forced copulation behavior was positively associated with testosterone, the first such demonstration for any species. Surprisingly, paired males were not more likely to attempt forced copulations than unpaired males, a result that was possibly an effect of captivity. Both pair status and testosterone, however, appeared to influence male courtship behavior. Unpaired males spent more time associated with females during these trials than did paired males. Moreover, there was a positive correlation between testosterone and the time that males spent associated with females. This relationship held for both paired and unpaired males. As both forced copulation and extra-pair courtship are polygynous tactics, these results add to the growing body of evidence that testosterone is involved in polygynous behavior.