Red-winged Blackbird males secure breeding territories in the early spring before females return from their southern wintering grounds. Males spend much of their time during the breeding season patrolling territorial boundaries and fending off intruders by performing wing-spread displays that highlight bright red shoulder patches. When the females return, they choose their mate partly on the quality of his territory, making sure that it has an abundant food supply of small arthropods, water for drinking and bathing, and tall grass for safe nesting sites. Because the top males can defend territories that safely support multiple nests, you will often find multiple females nesting within high-ranking male territories, making Red-winged Blackbirds one of the most recognizable examples of resource-defense polygyny in birds.

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