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. Male removal experiments and natural cases of polygyny indicated that females without male parental care produced fewer offspring in the area (Ontario) with less abundant food. Relative to their mates, males also fed their nestlings more often in Ontario than in Alberta. Despite the difference between areas in the relative importance of male parental care, we did not find more polygyny in Alberta than in Ontario. The lack of relationship between frequency of polygyny and the contribution of male parental care to offspring production suggests that other factors such as female-female competition can influence the level of sexual selection independently of sexual differences in parental investment.