A golden head, black wings with a white patch, and a call sounding like the opening of a rusty farm gate, Yellow-headed blackbirds demand your attention. In spring, these birds are to be found in a marsh or slough where the surrounding water offers safety but often serves to limit the nesting habitat, resulting in crowding. A number of males are always in a display flight, head stooped, their feet and tail drooped, their wings beating slowly, in an accentuated manner. Some quarrel with their neighbors over boundaries; others fly off to feed. Approaching predators get mobbed by bunches of Yellow-headed blackbirds and any neighboring Red-winged blackbirds, nesting in the drier cattails.
During summer, this species migrates north to go to the west-central areas of the United States and Canada. Its range extends to central-interior British Columbia in the far west, then directly south to the central-interior west coast and on to northeastern Baja California. In the east, the range runs from western Ontario to the north of Missouri. In winter, it is found from Texas to California and also in Mexico and as a casual visitor in Costa Rica. These birds inhabit freshwater marshes in the summer. They especially like to live amongst tule, cattails, and bulrush. At the time of migration and during winter they occur in open cultivated areas, in fields, and in pastures.
Yellow-headed blackbirds are diurnal and feed by gleaning seeds and insects from the ground and from plants, and by catching insects in the air. Their main technique of foraging is to dig their beak into the ground or into a food item and force their beak open, along with the substrate. These birds are strongly territorial in the breeding season. They like to nest in marshes above water that is two to four feet deep. Nests are usually located in a different section of a marsh from Red-winged blackbirds, which prefer nesting over shallower water. Their nests are sometimes destroyed by Marsh wrens, so the territorial males exclude these birds from their nesting areas. These blackbirds are gregarious, and often travel and roost in flocks. During the fall migration, males often gather in flocks separate from females and the young. In winter, they form enormous flocks along with other species.
These birds are polygynous and a single male can include as many as 16 females in his harem. Males are very territorial during the mating season, which is from May to June. The males arrive at the breeding grounds prior to the females in order to establish their territory, usually being 100 to 600 sq. m. Males which do not have females enter their territory in the breeding season will intrude on another male's territory, looking to mate. Territorial displays and courtship include boundary disputes when the bird's head turns to the side and not upwards. The female selects a nesting site and makes a woven bulky nest of wet vegetation over the water in the reeds. She lays 3 to 5 eggs of greenish-white with dark markings. Incubation is by the female for around 11 to 13 days. During the time on the nest, both parents will feed the young during the first four days, at least partly, by means of regurgitation. Nestlings are fed insects only. They remain for 9-12 days in the nest, but after leaving the nest they continue to be fed by their mother.
This species is not regarded as globally threatened, although certain populations are declining. Such declines may be a result of habitat degradation from agricultural chemical usage and wetland drainage. This bird's tendency to eat seeds from agricultural fields results in conflict with humans, with farmers trapping and shooting any found on their land. In addition, the pesticides and herbicides used in agriculture can be ingested when eating and can be very harmful to them.
According to the What Bird resource, the total population size of the Yellow-headed blackbird is around 23 million individuals. The All About Birds resource records that the size of the total breeding population of this species numbers 11 million individuals, 85% of them spending some part of their year in the U.S., with 75% in Mexico, and a further 15% breeding in Canada. Overall, currently, Yellow-headed blackbirds are classified as Least Concern (LC) on the IUCN Red List and their numbers today are increasing.
Due to their diet, these birds may affect insect populations in their range.