Non-Breeding Season Attributes of Male Dark-Eyed Juncos That Acquired Breeding Territories in Their First Year

In a mountain-breeding population of Dark-eyed Juncos Junco hyemalis, most young leave the mountaintop in winter. When males return in their first spring, some get breeding territories whereas others become floaters. In one spring we were able to compare territorial and non-territorial yearlings with respect to age, location(s) occupied in the preceding summer, arrival time in spring, and morphology. The two groups differed only in locations occupied. In a second spring we could analyze characteristics only of territorial yearling males. These had tended to exhibit site attachment in the preceding summer, and the majority had been encountered on the study area in the preceding Octo­ber; among the latter, most held territories next spring at an autumn site. Our findings suggest that male site attachment forms before or during autumn and that familiarity or a prior residence effect confers an advantage in territorial competition the following spring.