Molothrus aterbrown-headed cowbird
Geographic Range
Cowbirds breed from SE Alaska, through lower Canada, through the entire continental U.S. to central Mexico. They winter throughout this range, and also in southern Mexico and the tip of Florida.
Habitat
Cowbirds prefer habitats with low or scattered trees among grassland vegetation, such as woodland edges, brushy thickets, prairies, fields, pastures, orchards, and residential areas. Fragmentation of forests has greatly increased the Brown-headed Cowbirds favorite habitat.
- Terrestrial Biomes
- forest
Physical Description
The cowbird is a small blackbird with a short conical bill and long, pointed wings. Males appear black with a unique brown head and neck. Females are either dullish gray or brown throughout. The bill is a dull grey, while the eyes are black.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
-
- Range mass
- 40 to 50 g
- 1.41 to 1.76 oz
-
- Average basal metabolic rate
- 0.6315 W
- AnAge
Reproduction
The Brown-headed Cowbird is a brood parasite; the female cowbird selects a host nest of another species of bird to lay her eggs in. She wanders about, parasitizing many nests and laying up to 40 eggs per season. The young are then cared for by the host. 144 different host species have been documented to rear cowbird young, so the incubation and parental care of cowbirds varies greatly depending on the nest in which they are deposited. During the various care processes for the cowbirds, however, they are always fed more often than the young of the host species. The smallest recorded host of cowbird young is the 10 g creeper, while the largest host is the 150 g meadowlark.
- Key Reproductive Features
- iteroparous
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- oviparous
Lifespan / Longevity
-
- Average lifespan
Status: wild - 202 months
- Bird Banding Laboratory
- Average lifespan
Behavior
The cowbird rarely hops when on the ground, preferring to walk. It is often found in mixed-species flocks with other blackbirds, such as the Common Grackle. The cowbird gets its name from its close association with livestock, such as horses and cattle, which disturb insects on the ground when feeding. This allows cowbirds easy access to their food. Because cowbirds have a significant impact on the reproductive success of other species, many other bird species have adapted and can recognize this threat, acting aggressively to cowbirds near their nesting trerritory.
- Key Behaviors
- flies
- motile
Communication and Perception
Food Habits
Cowbirds often feed on the ground, away from vegetation. Their main food items are seeds and arthropods. They sometimes hawk, looking for slow flying insects. In a quantitative anaylsis of the cowbird diet, it was found that nearly 75% of the diet was 'weed' seed, with most of the remaining 25% made up of grasshoppers and beetles.
Economic Importance for Humans
Economic Importance for Humans: Positive
The cowbird eats many insects which are pests to humans.
Economic Importance for Humans: Negative
Fragmentation of forest habitats in North America has resulted in a great increase in the edge habitats favored by cowbirds, and a reduction (and in many places an elimination) of forest-interior habitats that cowbirds do not penetrate. As a result, a number of species of forest birds are now subject to increasing parasitism by cowbirds. Cowbird parasitism may be one cause in the general decrease in numbers of songbirds in North America.
Conservation Status
The cowbird is common. It does, however, pose a threat to the populations of other birds, such as the Kirtland's Warbler, Black-capped Vireo, and Least Bell's Vireo, whose small populations are frequently parasitized by the Brown-headed Cowbird. This has led to programs that involve trapping of the cowbirds at specific breeding areas where other species are threatened.
-
- IUCN Red List
-
Least Concern
More information
-
- US Migratory Bird Act
- Protected
-
- US Federal List
- No special status
-
- CITES
- No special status
-
- State of Michigan List
- No special status
Contributors
Jennifer Roof (author), University of Michigan-Ann Arbor.
Glossary
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- acoustic
-
uses sound to communicate
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- chemical
-
uses smells or other chemicals to communicate
- endothermic
-
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- motile
-
having the capacity to move from one place to another.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- tactile
-
uses touch to communicate
- visual
-
uses sight to communicate
References
Lowther, Peter E. The Birds of North America. No. 47, 1993. The American Ornithologists' Union.