Summary
Field experiments were conducted on a population of nesting Tree Swallows (Iridoprocne bicolor) to assess whether the evolved function of territoriality is to prevent breeding by conspecifics (superterritoriality). The size and orientation of territories were estimated by the response of birds to a conspecific model. There was no difference in territory size between birds that had the potential to defend surplus boxes and those that did not. Similarly, territorial defense was not oriented more toward the vicinity of surplus boxes than in other directions. These results indicate that territorial behavior has not evolved due to a relative increase in fitness that may be gained by preventing conspecifics from breeding.