Grackles |
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History and Biology: The Icterids are native to North America and come from a group of songbirds, nine-primaried oscines, thought to be of relatively recent origin and found mainly in the Americas. Grackles, blackbirds, and their allies (including cowbirds) are grouped together as one of the five groups of Icterids. There are three species of grackles in Texas, Common, Boat-tailed, and Great-tailed. They are blackish with yellowish eyes and differ from each other primarily in overall length. All three species can be differentiated from the Crow because the Crow is larger and has black eyes. Common grackles are about 12.5 inches in overall length. They have a long keel shaped tail and pale yellow eyes. Males have an iridescent purple cast to their head, neck, and breast. Females are smaller and duller brown. They have a long bill that is thinner than a crow's. Boat-tailed grackles are about 16.5 inches long. They have a longer keel shaped tail and yellow to brown eyes. Males are iridescent blue-black while females are smaller and tawny brown. They have a long bill that is thinner than a crow's. Great-tailed grackles are the largest grackle. They are about 18.5 inches in overall length with a very long keel-shaped tail and golden yellow eyes. Males have iridescent black and purple on the head, back, and breast. Females are brown with buff to grayish breasts. They have a long bill that is thinner than a crow's. Grackles have adapted to commensal relationship with humans and are expanding throughout North America. The Great-tailed Grackle is one of the fastest expanding species in North America. In the early part of the twentieth century it was only found along the United States and Mexico border. It now breeds nearly to Canada. The Common Grackle has spread westward across the continental divide into Idaho. Grackles forage mainly on the ground for insects (beetles, grubs, grasshoppers, caterpillars, and others), millipedes, spiders, earthworms, crayfish, minnows, frogs, the eggs and young of other birds, and small rodents. They also eat fruits, nuts, and seeds when not breeding. They are primarily insectivorous when breeding. Feed singly, in pairs and in large flocks in both breeding and non-breeding seasons. Grackles will pick insects off grills and bumpers of parked automobiles. They will also eat human garbage. Grackles have been observed taking dog food from dog feeding bowls around homes. Grackles build bulky cup nests of soft vegetative material. Grackles remain social throughout the year. They are highly variable in mating from monogamous pairs, polygamous, to Great-tailed grackle harems. Most nest in colonies of ten to thirty pairs in trees, usually in evergreens. They do not reuse nests. Grackles raise 1 to 3 broods per year of 4 to 5 eggs per clutch. Raising young is variable, one or both adults feed the young insects. Adult survival is 34% to 86%. Oldest grackle is a common grackle of 20 years 11 months. Grackles 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: Grackles 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. Grackles 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, grackles also harbor and transmit a number of ectoparasites associated with the bird and its nests such as lice, mites, fleas, ticks, and bugs. Structural Damage: Grackles roost in large flocks thereby defacing equipment, statues and buildings with excretory droppings and messy nest building. They also cause structural damage to agricultural barns and silos. They foul areas where people may walk and/or work. Grackle droppings and nests clog drain pipes, gutters, and air intakes, mar window sills, and render fire escapes hazardous, Nest building in electrical panels, junction boxes, and warehouse lights may cause short circuits and fires. Agricultural Damage: Grackles 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, Grackles are a serious and constant public health and property damage problem. Economic Damage: Economic damage from Grackles 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 architectural and structural damages from defacement, insulation loss and fire caused by the prolific nesting and feeding activities on and in anthropogenic structures and parks. Also there is a significant cost to American consumers and business from the consumption and contamination of seed and grain damaged by Grackles. 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 Mallis, A. 1997. Handbook of Pest Control: The behavior, Life History, and Control of Household Pests, Eighth Edition. Mallis Handbook and Technical Training Company. 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. 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. |
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