View Pictures of Bird Damage
Click the image for a larger picture	Class Aves Order Passeriformes Family Icteridae Molothrus ater

History and Biology:

Cowbirds, Grackles, Brewer's Blackbirds and their allies are grouped together as one of the five groups of Icterids. They are native to North America and come from a group of songbirds called the nine-primaried oscines. They are thought to be of relatively recent origin and found mainly in the Americas.

Cowbirds are medium sized, approximately 6 to 8 inches in overall length. The males are glossy black with dark brown head. Females are gray with paler throat. Both have dark eyes. The overall length of Cowbirds is shorter than that of the Grackle and they have a proportionately shorter tail. Cowbirds have a short conical shaped bill.

Cowbirds are predominantly in the southern half of the United States and extend into Mexico. They inhabit a wide variety of areas such as farmlands (particularly where livestock are found), groves, forest edges, and river woodlands. They have adapted a relationship with livestock where they walk along with the herd and nab the insects kicked up by the animals. In the past, Cowbirds followed great herds of bison on the plains, where they became known as "Buffalo birds."

Cowbirds are infamously known for their brood parasitism. They do not make a nest and do not care for their young. Instead, they lay an egg in a host nest, sometimes eating one of the host species eggs. The host bird then incubates and feeds the Cowbird chick as one of its own, some times to the demise of the smaller chicks from the host species. The foster parents feed the intruder until it can fly. Few birds are generally disapproved of as the Brown-Headed Cowbird because of this brood parasitism or predation character.

Cowbirds may be controlled without a federal or state depredation permit when found committing or about to commit depredation on ornamental or shade trees, agricultural crops, livestock, or wildlife, or when concentrated in numbers and in a manner that constitutes a health hazard or other nuisance.

Public Health Damage:

Cowbirds and their droppings create a serious and constant health problem. They may be a reservoir for the transmission of diseases to humans (zoonotic diseases) such as ornithosis, salmonellosis, and several forms of encephalitis, histoplasmosis, cryptococcosis, toxoplasmosis, and coccidiosis. Blackbirds are also a concern to farmers because they may carry and transmit many diseases, such as hog cholera, for livestock. In additional to the numerous infectious zoonotic diseases, Cowbirds also harbor and transmit a number of ectoparasites associated with the bird such as lice, mites, fleas, ticks, and bugs.

Structural Damage:

Cowbirds may roost and feed in large flocks thereby defacing equipment, statues and buildings with excretory droppings. They also cause structural damage to agricultural barns and silos. They foul areas where people may walk and/or work.

Agricultural Damage:

Cowbirds threaten the health of livestock in United States agriculture because they may be a reservoir for the potential transmission of many livestock diseases such as salmonella and hog cholera, especially around concentrated poultry and swine production facilities. They also do damage through the consumption and contamination of agricultural seed and grain products in the field, storage facilities, and wholesale and retail outlets.

Environmental Damage:

Because of their commensal relationship with humans and their potential for producing large flocks, Cowbirds are a serious and constant public health and property damage problem. Also, they are detrimental to native songbirds, such as flycatchers, sparrows, vitreos, and warblers because of their brood parasitism. Finally, ornithologists cite Cowbird brood parasitism as a major influence, along with habitat destruction, for the decline of many species. A female Cowbird may lay up to 40 eggs in a season.

Economic Damage:

Economic damage from Cowbirds is difficult to assess when you consider the intangible costs of the impact of zoonotic diseases on the public health of humans, livestock, and wildlife. Additionally, it is also difficult to determine the real cost of equipment and structural damages from defacement. Also there is a significant cost to American consumers and business from the consumption and contamination of seed, grain, and products damaged by Cowbirds.

References:

Coded Federal Registry, 50CFR17.Subpart D, Endangered and Threatened Wildlife and Plants

Coded Federal Registry, 50CFR 20.43, Wildlife and Fisheries, Hunting and Migratory Bird Regulations

Coded Federal Registry, 50 CFR 21.43 Subpart D, Control of Depredating Birds

Fergus, C., 2000, Wildlife of Pennsylvania and the Northeast, Stackpole Books, Mechanicsburg, PA 17055

Oklahoma Wildlife Conservation Commission, 2004-2005, Oklahoma Hunting Guide, Protected Species. Page 9. Oklahoma Department of Wildlife Conservation, P.O. Box 53465, Oklahoma City, OK 73152.

Perrins, C. and Harrison, C.J.O. 1979. Birds: Their life, Their Ways, Their World. Reader's Digest Edition, The Reader's Digest Association, Inc. Pleasantville, N.Y.

Sibley, D.A., 2001, The Sibley Guide to Bird Life and Behavior, National Audubon Society, Alfred A Knopf, N.Y.

Texas Parks and Wildlife Department, 2004, Hunting and Fishing Regulations, Endangered, Threatened, and Other Protected Nongame Species, Protected and Unprotected Birds, Texas Parks and wildlife, 4200 Smith School Road, Austin, Texas 78744.

Wernert, S. J., 1982. North American Wildlife, The Reader's Digest Association, Inc. Pleasantville, N.Y.