The brown-headed cowbird (Molothrus ater ) is a small, obligate brood parasitic icterid native to temperate and subtropical North America. It is a permanent resident in the southern parts of its range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat around March or April.
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DiurnalDiurnal animals are active during the daytime, with a period of sleeping or other inactivity at night. The timing of activity by an animal depends ...
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HerbivoreA herbivore is an animal anatomically and physiologically adapted to eating plant material, for example, foliage, for the main component of its die...
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FrugivoreA frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts, and seeds. Approx...
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GranivoreSeed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds of pla...
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ArborealArboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some anima...
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ZoochoryZoochory animals are those that can disperse plant seeds in several ways. Seeds can be transported on the outside of vertebrate animals (mostly mam...
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
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TerritorialA territory is a sociographical area that which an animal consistently defends against the conspecific competition (or, occasionally, against anima...
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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CongregatoryCongregatory animals tend to gather in large numbers in specific areas as breeding colonies, for feeding, or for resting.
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MonogamyMonogamy is a form of relationship in which both the male and the female has only one partner. This pair may cohabitate in an area or territory for...
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PolygynandryPolygynandry is a mating system in which both males and females have multiple mating partners during a breeding season.
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FlockingFlocking birds are those that tend to gather to forage or travel collectively. Avian flocks are typically associated with migration. Flocking also ...
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Dominance hierarchyA dominance hierarchy (formerly and colloquially called a pecking order) is a type of social hierarchy that arises when members of animal social gr...
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Partial MigrantPartial migration is when within a migratory species or even within a single population, some individuals migrate while others do not.
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starts withThe Brown-headed cowbird is a sturdy blackbird with an unusual approach to parenthood. Females do not build nests but use all their energy for producing eggs, sometimes over three dozen per summer. They lay their eggs in other birds’ nests, who become their chicks’ foster parents, with usually at least some of their foster parents’ chicks being victims in the process. Heavy parasitism by this species has pushed some birds to be "endangered" and has affected other populations as well.
Brown-headed cowbirds live throughout the United States, most of Canada, and Mexico. They are permanent residents in the southern parts of their range, while northern birds migrate to the southern United States and Mexico in winter. Brown-headed cowbirds prefer habitats with scattered or low trees among grassland vegetation, like brushy thickets and woodland edges, as well as meadows, pastures, fields, orchards, and residential areas.
These birds are social but are usually more solitary during the mornings, which is when mating occurs. Females also seek host nests in the mornings. During the afternoons, birds gather in flocks to forage. They walk on the ground to forage, feeding away from vegetation. In winter, they congregate in very big flocks with European starlings and other icterids. Roosting populations may number up to 38 million individuals. A hierarchy is established in social settings based on how many displacements, flight whistles and song spreads there are in the repertoire of a male. To determine hierarchy, cowbirds participate in "triangle and quadrangle ceremonies", during which males stand in a circle and perform song spreads. After the social status is determined, it is usually maintained by nonverbal means. Singing in flocks is mostly performed by the dominant male and this may be enforced, if inferior males try to sing, by attacking them.
Brown-headed cowbirds are herbivores (frugivores and granivores). They eat mostly fruits and seeds. Also in their diet are eggs, spiders, and arthropods, like grasshoppers, leafhoppers, and beetles. Females supplement their diet with mollusk shells during the breeding season.
Almost all populations of Brown-headed cowbirds have fewer females than males, so the females may be choosy. Males are usually monogamous for the breeding season and attempt to maintain this by guarding their mate from other males. However, females tend to be polygynandrous or promiscuous. When outside her mate's home range, a female is no longer guarded, so may copulate with a different male. Males not in a pair-bond sometimes mate with females that are not guarded, often while the female's mate is away foraging. Copulations amongst non-mates are more frequent in those populations where the females have more extensive home ranges than the males. The breeding season will vary with the region, but eggs are laid in May and June. One female lays up to 40 eggs each year in the nests of other species. They find nests by quietly watching for signs of nest building, or they flutter through the vegetation, aiming to flush the nest builders out. The incubation time is only 10 to 12 days. After 8 to 13 days the chicks leave the nest and are fully independent from their hosts at around 25 to 29 days old.
The Brown-headed cowbird is widespread and does not face any major threats at present; however, it has some predators, such as hawks, owls, raccoons, squirrels, and snakes. Other reasons for its population decline are unknown.
According to the What Bird resource, the total population size of the Brown-headed cowbird is around 56 million individual birds. The All About Birds resource records the species’ total breeding population size as 120 million individuals. Overall, currently, Brown-headed cowbirds are classified as Least Concern (LC) on the IUCN Red List, but their numbers today are decreasing.
Social animals are those animals that interact highly with other animals, usually of their own species (conspecifics), to the point of having a rec...