Residency: Year-round in southeastern Arizona. In winter: only in southwestern Arizona. In summer: will reside all the way in the northern part of the state.
Diet: Insects, grain, grass and weed seeds. Feeds off the ground, but will also visit seed feeders. In the past, cowbirds used to feed on the bugs on bison. Today they often feed alongside horses and cows.
Predators: Direct predators of the fledglings include: black racers, black rat snake, and Blue Jays. Eggs are also destroyed by host species, since the cowbird lays all her eggs in the nests of other species. Host species may reject the cowbird egg in one of several ways: ejecting them from from the nest, burying them, or deserting the nest entirely. The followin species almost always reject cowbird eggs: Western Kingbird, Eastern Kingbird, Blue Jay, American Robin, Gray Catbird, Brown Thrasher, Cedar Waxwing, and Northern Oriole. Most other hosts reject less frequently.
Nesting: Has no nest of its own, but instead lays her eggs in the nests of other species (parasitism ? see predators section above, and notes section below). She lays 5-7 eggs per breeding session, but usually only one egg per host nest. The eggs are white with dark markings (brown or gray).
Nesting Records:
Notes: A member of the Blackbird family, the Brown-headed Cowbird is one of the only two parasitic bird species in Arizona, and the only brood parasite common across North America. The female will lay her eggs in the nests of other bird species (known to parasite more than 200 species), which reduces the reproductive success of the other species. Most of these host species (called "acceptors") will incubate the cowbird eggs and raise the young, even at the exclusion of their own young. The remaining species (known as the "rejectors") will reject the cowbird eggs most of the time.
