Parental investment and pair-bond behavior among canvasback ducks (Aythya valisineria, Anatidae)

Abstract

Hypothetical patterns of male and female cumulative reproductive effort in canvasback ducks were used to predict the efforts of males and females in pair-bond reinforcing behavior through a breeding sequence. The predictions were that, at any point in time in a monogamous breeding system, given certain assumptions, (a) the sex investing less should be more active in reinforcing the pair bond, and (b) this relationship should shift within and between breeding attempts with the pattern of cumulative reproductive effort per brood by the male and female. Data on the behavior of newly-formed pairs were obtained by observing apparently paired but unmarked canvasbacks during spring migration. Later, 11 individuallymarked pairs were followed through breeding sequences, including repeated nesting attempts. Observed affiliative behavior fit the predictions reasonably well. That sex whose cumulative reproductive effort was less tended to be more active in maintaining proximity to its mate, initiating bouts of mutual display, and coordinating pair activities. Predictions were met in 14 of 24 cases, results were contrary in 3 cases, and in 7 cases trends were not statistically different (P>0.05). Shifts in relative male and female reinforcement efforts that coincided with major changes in investment were apparent. These results support the proposition that factors other than simple parental investment-related desertion costs might be important to an individual's behavioral ‘decisions’ regarding pairbond reinforcement and ultimately mate abandonment. Discrepancies in a few predicted outcomes further suggest that males and females may use and balance various pair-reinforcement tactics differently through a breeding season.