Abstract
Phylogenetic constraint and inertia, i.e. limitations on future evolutionary trajectories imposed by previous adaptation, are often invoked to explain behavioural, morphological and physiological traits that defy explanation in an adaptive context. We reconstructed historical changes in male parental care behaviour in the dabbling ducks (family: Anatidae; tribe: Anatini) using a phylogeny based on mitochondrial DNA sequences. Male parental care is observed in many tropical and Southern hemisphere dabbling ducks but is lacking in all Northern hemisphere species. Southern hemisphere species that are very recently derived from Northern hemisphere ancestors, however, are exceptions to this general pattern. Lack of male parental care in these species can be attributed to phylogenetic constraint.