Spring roosting dynamics of red-winged blackbirds: biological and management implications

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Abstract
Monitoring of changes in size and composition of a spring blackbird roost near Beauharnois, Quebec, indicated that the roost became active in the middle of March and that most birds had dispersed by late April. Throughout the roosting period, red-winged blackbirds (Agelaius phoeniceus) constituted approximately 74% of the roosting population. The patterns of arrival and dispersal from the roost by the different age–sex cohorts of the red-winged blackbird reflected the intensity of sexual selection on this polygynous species. Older males were first to arrive but dispersed to establish breeding territories soon thereafter. Second-year males exhibited a less abrupt pattern of arrival and dispersal than older males while the pattern for females was even less abrupt. The implications of these patterns for management schemes aimed at reducing spring populations are discussed.