Brown-Headed Cowbird (Molothrus ater)


Group	Blackbirds
Code	ABPBXB7030
Order	Passeriformes
Family	Icteridae
Author	(Boddaert, 1783)
Rank	G5 (definitions)
Occurrence	SM (definitions)
Scale	N (definitions)

County List:


Western UP	all
Eastern UP	all
Northern LP	all
Southern LP	all

Rule:

Forested or Nonforested Landscapes

      (Any Upland Deciduous (Regen))
      or (Any Upland Conifer (Regen))
      or (Any Upland Mixed (Regen))
      or Grass
      or Upland Brush
      or Small Grains/Forage Crops
      or Fields/Pastures
      or Savanna
      or Edge

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Habitat List:

Habitats	Regen	Sap	Pole	Sm Saw	Lg Saw	Uneven
Aspen	YES	no	no	no	no	-
Paper Birch	YES	no	no	no	no	-
Oak	YES	no	no	no	no	no
Assorted Hardwoods	YES	no	no	no	no	no
Northern Hardwoods	YES	no	no	no	no	no
Spruce/Fir	YES	no	no	no	no	no
Hemlock	YES	no	no	no	no	no
Jack Pine	YES	no	no	no	no	no
Red Pine	YES	no	no	no	no	no
White Pine	YES	no	no	no	no	no
Conifer Plantations	YES	no	no	no	no	-
Mixed Upland Hardwoods	YES	no	no	no	no	no
Mixed Northern Hardwoods	YES	no	no	no	no	no
Mixed Upland Conifer	YES	no	no	no	no	no
Mixed Pine	YES	no	no	no	no	no
Swamp Hardwoods	no	no	no	no	no	no
Balsam Poplar & Swamp Aspen & Swamp Birch	no	no	no	no	no	no
Bottomland Hardwoods	no	no	no	no	no	no
Tamarack	no	no	no	no	no	no
Northern White Cedar	no	no	no	no	no	no
Black Spruce	no	no	no	no	no	no
Mixed Lowland Hardwoods	no	no	no	no	no	no
Mixed Lowland Conifer	no	no	no	no	no	no
Non-Forested	Grass, Upland Brush, Savanna, Small Grains/Forage Crops, Fields/Pastures
Special Features	Edges

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Literature:

Walkinshaw, L. H. 1991. Brown-headed Cowbird. Pages 508-509 In: R. Brewer, G. A. McPeek, and R. J. Adams, Jr. (eds.) The atlas of breeding birds of Michigan. Michigan State University Press, East Lansing. 594 pp.

Habitat: The Brown-headed Cowbird forages mainly in open country, where it eats seeds and insects. Formerly it associated with the bison in the West and later with cattle, but even this association is less important today. The cowbird is more prevalent in farming communities in southern Michigan, jack-pine plains in the northern Lower Peninsula, and residential areas in the Upper Peninsula. In the Atlas Habitat Survey, one-third of all records were from residential-roadside-hedgerow habitats and the rest were spread through 13 other categories.

It will lay its eggs in nests in fields but it also utilizes forest and edge habitats. More than 40 host species have been reported in Michigan, but the cowbird is rather selective in the species it parasitizes. It selects the Field Sparrow over the Chipping Sparrow and the Kirtland's Warbler over both. In forest habitats, Red-eyed Vireo, Acadian Flycatcher, and Ovenbird are frequently parasitized. From my experience, hosts with white spotted eggs are preferred to those with blue. Cowbirds also seem to prefer nests where the eggs are no larger than their own and eggs of species with long incubation periods.

The cowbird has also been implicated in the decline of certain birds of the eastern deciduous forest, as the result of forest fragmentation. There is some evidence that nests are more apt to be parasitized near forest openings and edges than in deep forest. I have never found a parasitized nest of any bird in a large bog or continuous forest in northern Michigan.

DeGraaf, R. M. and D. D. Rudis. 1986. New England wildlife: habitat, natural history, and distribution. GTR NE-108. Broomall, PA:USDA, Forest Service, Northeastern Forest Experiment Station. 491 pp.

Breeding: Open coniferous and deciduous woodlands, forest edges, agricultural land, suburban areas. Wintering: Agricultural lands, feeding stations.

Kaufman, K. 1996. Lives of North American Birds. Houghton Mifflin Company, Boston, Massachusetts. 675 pp.

Habitat: Farms, fields, prairies, wood edges, river groves. Favors open or semi-open country at all seasons. In winter, often concentrates in farmland, pastures or feedlots, where foraging is easy. More widespread in breeding season, in grassland, brushy country, forest edges, even desert, but tends to avoid dense unbroken forest.

Diet: Mostly seeds and insects. Seeds (including those of grasses, weeds, and waste grain) make up about half of diet in summer and more than 90 percent in winter. Rest of diet is mostly insects, especially grasshoppers, beetles, and caterpillars, plus many others, also spiders and millipedes.