Influence of population size on habitat use by territorial male red- winged blackbirds in agricultural landscapes

Examined the distribution among habitats of male Agelaius phoeniceus at relatively low (26 males/km² in 1978) and high (45 males/km² in 1979) overall population densities. Wetlands and hayfields were the most suitable breeding habitats; 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' (1970) model, but their model did not account for some aspects of spacing behaviour, because habitat imprinting, site fidelity and chance events, in addition to territorial behaviour, likely contributed also to the spacing patterns. -from Authors