Content for this page researched and created by Matthew Kasanicky
The Brown-headed Cowbird (Molothrus ater) is a black colored bird that is about six to eight inches in height. The males and females of this species differ in appearance. The male birds are a glossy black coloring with a brown head, and the females are a brown and gray mixed color (Cagan, Joanna). These birds have thick black bills that resemble the bills of finches (Brown-Headed). The juvenile Brown-headed Cowbird resembles more of the adult female Brown-headed Cowbird, but it is more of a brown color than the adult female. The Brown-headed Cowbird is very similar to other cowbirds, although the brown-head on the male separates it from other species. The Brown-headed Cowbird is not much of a songbird although the females have a quiet chatter noise and males whistle usually after taking off for flight. They make some of the highest sound frequencies of any bird species (Brown-Headed).
Brown-headed Cowbirds are mostly seen and heard around herds of cattle that are grazing in pastures and stockyards (Pooler, Harriet). The Brown-headed Cowbirds originated on the great plains of the United States (Molothrus Ater). Today these birds can be found from coast-to-coast in North America. The Brown-headed Cowbirds have widened their range of habitat due to the decrease in forested land area caused by European colonization and massive land clearing for agriculture (Bent, Arthur).
Brown-headed Cowbirds are short-distance migrating birds that try to stay close to their mating areas (King, Andrew). Mating occurs mostly in the spring months. In the winter months, the Brown-headed Cowbird can be found in open fields around herds of cattle and agriculturally influenced areas.( Molothrus Molothrus)
Brown-headed Cowbirds primarily feed on the ground. They eat organisms such as insects and also seeds from the wastes of the herds they follow. The females must consume a higher calcium diet due to a number of eggs they lay. The females will eat other organisms outside the birds ordinary diet such as snail shells and other bird’s eggshells in order to satisfy their dietary calcium requirements (Pooler, Harriett). Studies looking at the influence of dietary calcium have shown that when the amount of dietary calcium was reduced, there was a half a percentage decrease in the production of eggs ( HOLFORD, KENNETH).
The Brown-headed Cowbird has unusual nesting habits. Unlike most birds, they use “host nests” instead of building their own. Brown-headed Cowbirds travel to other birds’ nests to lay their eggs (Chipper Woods). The female cowbirds are essentially parasites on the host birds. The female Brown-headed Cowbird will actively observe the nesting patterns of other species to scout potential host nests (Banks, Alison). Once a potential host nest is left unguarded, the female Brown-headed Cowbird will go to the nest and toss out one of the host bird’s eggs and lay one of her eggs in the nest (Bent, Arthur). Studies have shown that cowbirds tend to parasitize certain species over others. Commonly chosen species are the Dickcissels, Grasshopper Sparrows, and the Eastern Meadowlarks, but many dozens of other species may be parasitized by Brown-headed Cowbirds ( Latham, Alexandra). There are multiple reasons why these birds appear to be more suitable to the Brown-headed Cowbird than others. The birds listed first are smaller than the Brown-headed Cowbird. The difference in size makes it easier for cowbird to fight for the nest if the original nesting bird returns while the Brown-headed Cowbird is found laying her eggs. Also, the Brown-headed Cowbirds have instinctive mothering behaviors. (Latham, Alexandra)
The Brown-headed Cowbirds are significant pests and threats to many other bird species throughout North America. Many times the Brown-headed Cowbird’s egg will be the only egg that the host bird cares for ( Rothstein, Stephen). The process the Brown-headed Cowbird utilizes to reproduce can greatly reduce the reproductive rates of other species of birds (Mayfield, Harold.). Brownheaded cowbirds are pushing many bird species toward extinction because of the intensity of their nesting practices. Brown-headed Cowbird can lay up to 80 eggs during a single mating season (Chipper Woods).
It is thought that once the Brown-headed Cowbird laid its eggs in a nest that it had created for themselves. the dependence of these prairie birds on the traveling herds of bison, though, selected for a more mobile activity pattern and an increasing reliance on nest parasitism (Bent, Arthur).
Numbers of the Brown-headed Cowbirds are declining. Re-establishment of forest habitats have had negative impacts this grassland dwelling species. This on-going process is also taking a toll on other species of birds as well, but Brown-headed Cowbirds seem to be more severely affected than other bird species.
Studies have shown that the host bird’s offspring numbers are increasing. As a whole, these factors have a negative impact on the growth of the cowbirds ( Cox, W. Andrew). There is more than just the re-forestation issue facing these birds. The Brown-headed Cowbirds carry a significant loads of parasitic mites. Although the presence of these mites do not seem to affect the cowbird’s flight abilities, the mites are slowly taking the lives of many Brown-headed Cowbirds ( Spalding, Marilyn). In areas without significant mite populations preying on wild bird species, the effect is exactly the opposite on Brown-headed Cowbirds as their population is rapidly increasing (Chipper Woods).
Scientists are exploring methods associated with the Brown-headed Cowbirds lifestyle in an attempt to decrease the number of eggs the female birds are laying. They have tested feeding patterns related to amount of calcium the cowbirds consume, as mentioned earlier. Tests were conducted to see if it was possible to limit the amount of eggs laid by the birds (HOLFORD, KENNETH). The scientists have also tried to find ways to make the host birds remove the eggs themselves, unfortunately this only happened with larger birds than the cowbird and results in the Brown-headed Cowbird laying their eggs in a nests of smaller birds (Winter, Stephen). The Brown-headed Cowbird does not offer a number of positive characteristics to the ecosystem as a whole, but their impact on host bird populations have been severe ( Cagan, Joanna).
Work cited
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Ater).” Columbia. Alberta Research council, 1 Mar. 2002. Web. 26 Sept. 2016.
Pooler, Harriett. “The Brown-Headed Cowbird.” Country Roads Magazine. Metro Publisher, 23 Apr. 2013. Web. 26 Sept. 2016.
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Ornithology, 2010. Web. 26 Sept. 2016.
Bent, Arthur C. “Brown-headed Cowbird.” Life Histories of Familiar North American Birds.
Smithsonian Institution United States National Museum Bulletin, 1958. Web. 26 Sept. 2016.
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(1977): 107-14. Sora.unm.edu. Web. 26 Sept. 2016.
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Brown-Headed Cowbird (Molothrus Ater) Populations Are Associated with
Landscape-Specific Reductions in Brood Parasitism and Increases in Songbird Productivity.” 7.10 (2012): n.p. Web. 26 Sept. 2016
King, Andrew P., Meredith J. West, and David J. White. “Female Cowbird Song Perception:
Evidence for Plasticity of Preference.” Department of Psychology , Indiana University,
Bloomington, IN, USA (2003): 1-13. Print.
Rothstein, Stephen I. “Brown-headed Cowbird Villain or Scapegoat?” TRASH BIRDS
(2004): 374-84. AMERICAN BIRDING. Birding Magazine, Aug. 2004. Web. 26 Sept.
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Spalding, Marilyn G., James W. Mertins, Matthew J. Reetz, Kandy L. Keacher, Michael L.
Avery, and Ellis C. Greiner. “Mite-Filled Cyst on a Brown-headed Cowbird (Molothrus
Ater) in Florida, USA.” Journal of Wildlife Diseases 46.4 (2010): 1279-285. Web.
White, David J., Julie Gros-Louis, Andrew P. King, Mara P. Papakhian, and Meredith J.
West. “Constructing Culture in Cowbirds (Molothrus Ater).” Journal of Comparative
Psychology 121.2 (2006): 113-22. PDF.
Winter, Stephen L., and Jack F. Cully, Jr. “Lack of Brown-Headed Cowbird Nest Parasitism in a Short
Grass Region.” University of Nebraska – Lincoln DigitalCommons@University of Nebraska – Lincoln (2005): n. pag. Web.
Images
(Use via Creative Commons)
- Male Brown-headed Cowbird Flickr. Yahoo . 2013 Web. 14 may, 2016.
- Female Brown-headed Cowbird on ground
Flickr. Yahoo . 2013 Web. 15 june, 2016.
- Juvilan Brown-headed Cowbird in feeder
Flickr. Yahoo . 2010 Web. 23 july, 2016.
- Brown-headed Cowbird in tree
Flickr. Yahoo . 2013 Web. 31 may, 2016.
- Three Brown-headed Cowbird
Flickr. Yahoo . 2009 Web. 30 may, 2016.