Summary
Movements of nonterritorial ("floater") male red-winged blackbirds (Agelaius phoeniceus) were monitored to test the hypothesis that floaters enhance their chances for territory acquisition by becoming familiar with a specific area, i.e., by restricting their geographical movements and monitoring only a few occupied territories. Intensive observations from two separate study areas did not support the hypothesis. Only 8% of the 410 males banded as floaters in an unmanipulated study area claimed territories or were ever recaptured on that study area, suggesting that floaters visited a very large number of territories. When territory owners were experimentally removed in a second study area, a greater proportion of floaters remained in the vicinity (29% of 80 males), indicating that one proximate control of floater dispersal was the availability of vacancies. Radiotelemetry confirmed that floaters ranged widely. Floaters continued to disperse as they aged, and most floaters that acquired territories probably did so outside the study areas. These patterns of dispersal and territory acquisition suggest that familiarity with a small number of territories and their owners is not a better strategy than continual dispersal for most floater red-winged blackbirds in these populations. Once adulthood was reached, younger floaters were not less successful than older floaters at claiming vacancies. This, combined with the effects of mortality, results in the majority of floaters and the majority of new territory claimants being young adult males.
Methodology
We studied red-winged blackbirds near the Queen's University Biological Station (45"37'N, 76'13'W; Fig. 1). We used a woodland study area where data on floaters have been gathered opportunistically as part of a larger study begun in 1985, and a roadside study area where data were gathered from 1988 to 1990 specifically for the purpose of studying floaters. The two study areas were separated by approximately 7 km, and birds banded in one study area have not been seen in the other study area in this or previous investigations (Eckert and Weatherhead 1987a; Muma and Weatherhead 1989). The data we report are for marked floaters that were identified when they visited a territory, were recaptured, or acquired a territory. Data were obtained between early April and mid-July in each year. Procedures differed between the two study areas, so we present the respective methods separately.