Influence of Population Size on Habitat Use by Territorial Male Red-Winged Blackbirds in Agricultural Landscapes

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Abstract
Fretwell and Lucas's (1970) model relating settling patterns and habitat suitability was tested by examining the distribution among habitats of male Red-winged Blackbirds (Agelaius phoeniceus) at relatively low (26 males/km2 in 1978)a nd high (45 males/km2 in 1979)overall population densities. Wetlands and hayfields were identified as the most suitable breeding habitats on the basis of habitat selection patterns of territorial males and other evidence, whereas forest, cropland, and human-occupied areas generally were avoided. Some "packing" of males into hayfields occurred when population level increased, but the greatest changes were recorded from less suitable habitats. Occupancy of wetlands and hayfields remained relatively stable. These results were in general accordance with predictions from Fretwell and Lucas's model, but their model did not account for some aspects of spacing behavior. This is because habitat imprinting, site fidelity, and chance events, in addition to territorial behavior, likely contributed also to the spacing patterns of male Red-winged Blackbirds observed.

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