The Yellow-headed Blackbird often nests in the same marsh as the Red-winged Blackbird. The larger Yellow-headed Blackbird is dominant to the Red-winged Blackbird, and displaces the smaller blackbird from the prime nesting spots. The Yellow-headed Blackbird is strongly aggressive toward Marsh Wrens too, probably because of the egg-destroying habits of the wrens. When the Yellow-headed Blackbird finishes breeding and leaves the marsh, Marsh Wrens expand into former blackbird territories.

The male Yellow-headed Blackbird defends a small territory of prime nesting reeds. He may attract up to eight females to nest within his area. The male helps feed nestlings, but usually only in the first nest established in his territory. The other females have to feed their young all by themselves.