FACTORS AFFECTING WHICH MALE RED-WINGED BLACKBIRDS ACQUIRE TERRITORIES

We use data from a 14-year study of dispersal, territoriality, and breeding success to investigate territory acquisition in male Red-winged Blackbirds (Agelaius phoeniceus). Males born in our study area that we later detected breeding had dispersed an average of about 1,400 m and had traversed an average of 25 territories between natal and breeding sites. Our data indicate that all or most males that bred within our study area were probably born no more than 5 km away. Some natal-year cohorts contributed disproportionately to the population of male breeders, suggesting that population structure influenced territory ownership. Most males that obtained territories did so when two years old (their first adult year), but a significant fraction spent at least one adult year as nonterritorial floaters. Our results are consistent with the hypothesis that familiarity with particular areas contributes to territory ownership, but we found no evidence that Resource Holding Potential is a prime determinant of territory acquisition. Chance events may also strongly influence ability to gain a territory.