ABSTRACT
Abstract. Sea ducks in tribe Mergini exhibit a wide range of spacing, breeding, and broodrearing behaviors and have provided important insights in both theoretical and applied behavioral ecology. The strength, timing, and duration of pairing vary among species. Longterm pair bonds of more than one year are common but the proportion of birds that repair annually is unknown. At least two pairing periods have been documented-one in fall, likely involving birds that are reuniting, and one in spring representing new pair formation. Courtship behaviors are diverse and spectacular but their ontogeny from juveniles to adult birds has not been described. Sea ducks have one of the largest gradients in pair spacing behavior among aquatic birds, ranging from a lack of pronounced spacing in the colonial Common Eider to extremely well-developed intra-and interspecic territorial behaviors in goldeneyes and Bufeheads. Brood spacing behavior ranges from the crèching behavior of Common Eiders to the highly developed territorial system of goldeneyes. The frequency of conspecic brood parasitism (CBP) is high in species that are cavity nesting or that nest in high densities, but
uncommon in species nesting at low densities in dispersed ground nests. Strong female natal and breeding philopatry results in various levels of kinship between parasites and hosts suggesting that CBP may also constitute cooperation among generations of closely related females. We review the evidence supporting various models and hypotheses attempting to explain CBP. There is increasing evidence that nest-site quality or host quality may be important factors inuencing how and where females lay their eggs. Interspecic brood parasitism is found in the same species for which CBP occurs, suggesting that there may be common ecological factors that inuence both behaviors. Brood amalgamation (BA) after hatch is more frequent in cavity-nesting sea ducks and ground-nesting species that nest in high densities and rare or occasional in ground-nesting species that nest at low densities. Interestingly, BA occurs more frequently in those species in which CBP is also more common. Whether BA is the result of accidental mixing or has an adaptive basis is still debated, but studies suggest differences in benets or costs of BA among populations and years. As for CBP, kinship may also play a role
in BA but evidence is equivocal. Unfortunately, we still know little about many of these species and our understanding of their social and reproductive ecology is based on detailed studies of less than half of the species in the tribe. The great behavioral diversity of ducks within the tribe Mergini offers a rich opportunity to explore the threads of physiology, ecology, and
evolution that underlie a complex and intriguing spectrum of reproductive behaviors.
