Territoriality among male red-winged blackbirds

Summary We examined male site fidelity and territorial movements in a population of individuallyidentifiable red-winged blackbirds (Agelaius phoeniceus) over an 8-year period. Based on general theory and knowledge of the ecology of this population, we predicted that males would be site conservative, and that they would voluntarily change territories only when they could expect to improve significantly their reproductive success. Because males are absent from their territories for only short periods, and probably have accurate comparative information only about nearby territories on which to base their decisions, we predicted that most moves would be over short distances. About 70% of males that bred for more than 1 year retained their original territories between breeding years. Most of the 30% of males that changed territories moved less than 200 m, often to adjacent territories. As predicted, males moving less than 200 m tended to have better reproductive success after moving than before, whereas long distance movers did not improve their success after moving. Territorial male redwings appear to monitor breeding activity on nearby territories and move when significant potential benefits are perceived and opportunities exist. Long-distance moves may be involuntary ones. The amount of information possessed about present and alternative sites, and the time and opportunity required to collect the information, are probably major constraints influencing site conservatism in this and other territorial species.