Effect of Intrusion Pressure on Territory Size in Black-chinned Hummingbirds (Archilochus Alexandri)

successful, however, and I believe that successful rapes ending in sperm transfer are rare. I never found semen deposition on the Cliff Swallow model, although similar studies by other investigators have found semen near the cloacal region of model Bank Swallows (Hoogland and Sherman 1976) and Savannah Sparrows (Passerculus andwichensis) (Weatherhead and Robertson 1980). Females might increase or decrease their fitness by participating in extra-pair copulations with males of unknown fitness. Presumably, it is to the female's advantage to copulate conservatively with males of known fitness (i.e. their mates) and not to risk decreased fitness by mating with other males. J.P. Goossen assisted in the field, J.P. Savard and G. E. J. Smith provided statistical advice, R. J. Cannings from the Vertebrate Museum at the University of British Columbia supplied some Cliff Swallow models, and M.D. Beecher, D. R. Flook, K. Vermeer, and P. Weatherhead commented on the manuscript. I thank all of you. LITERATURE CITED