Geographic variation in the importance of male parental care and mating systems in tree swallows

Sexual selection and mating systems are thought to be influenced by the relative contribution of the sexes toward production of offspring. Food abundance should influence the value of each sex's contribution to the production of offspring and, thereby, the level of sexual selection. We examined this hypothesis in two populations (Alberta and Ontario, Canada) of tree swallows (Tachycineta bicolor) that differed greatly in food abundance.