Common grackle

The common grackle (Quiscalus quiscula) is a species of large icterid bird found in large numbers through much of North America. First described in 1758 by Carl Linnaeus, the common grackle has three subspecies. Adult common grackles have a long and dark bill, pale yellow eyes, and a long tail. Adults often have an iridescent appearance on their head, especially males. Common grackles can be found widely across North America east of the Rocky Mountains.

Taxonomy
The common grackle was first described in 1758 by Carl Linnaeus in the tenth edition of Systema Naturae, as Gracula quiscula. It was assigned to the genus Quiscalus by French ornithologist Louis Pierre Vieillot in his 1816 Dictionnaire d'histoire naturelle.

Three subspecies are recognized:


 * the Florida grackle (Q. q. quiscula) (Linnaeus 1758), the nominate subspecies
 * the purple grackle (Q. q. stonei) (Chapman, 1935)
 * the bronzed grackle (Q. q. versicolor) (Vieillot, 1816)

Description


Adult common grackles measure from 28 to 34 cm in length, span 36 - 46 cm across the wings, and weigh 74 - 142 g. Common grackles are less sexually dimorphic than larger grackle species, but the differences between the sexes can still be noticeable. The male, which averages 122 g, is larger than the female, at an average of 94 g. Adults have a long, dark bill, pale yellowish eyes, and a long tail; their feathers appear black with purple, green, or blue iridescence on the head, and primarily bronze sheen in the body plumage. Adult females, beyond being smaller, are usually less iridescent; their tails in particular are shorter, and unlike the males, do not keel (display a longitudinal ridge) in flight and are brown with no purple or blue gloss. Juveniles are brown with dark brown eyes.

When grackles are in a group, they are referred to as a "plague".

Distribution and habitat
The breeding habitat is open and semiopen areas across North America east of the Rocky Mountains. The nest is a well-concealed cup in dense trees (particularly pine) or shrubs, usually near water; sometimes, the common grackle nests in cavities or in man-made structures. It often nests in colonies, some being quite large. Bird houses are also a suitable nesting site. Four to seven eggs are in a clutch.

This bird is a permanent resident in much of its range. Northern birds migrate in flocks to the Southeastern United States. The distribution of the common grackle is largely explained by annual mean temperature, and the species has expanded its range by greater than three-fold since the last glacial maximum, approximately 22,000 years ago.

Foraging and diet
The common grackle forages on the ground, in shallow water, or in shrubs; it may steal food from other birds. It is omnivorous, eating insects, minnows, frogs, eggs, berries, seeds, grain, and even small birds and rodents. Grackles at outdoor eating areas often wait eagerly until someone drops some food. They rush forward and try to grab it, often snatching food out of the beak of another bird. Grackles prefer to eat from the ground at bird feeders, making scattered seed an excellent choice of food for them. Grackles can be regularly seen foraging for insects, especially after a lawn trimming.

Grackles have a unique adaptation in the keel within their bill which allows them to crack and cut hard nuts or kernels. The keel projects downward from the horny palate and is sharper and more abrupt anterior. It extends below the level of the tomium and is used in a sawing motion to score open acorns or dried kernels. Larger adductor muscles within their jaw compared to those of other icterids make this adaptation even more useful for opening hard seeds and acorns.

Along with some other species of grackles, the common grackle is known to practice "anting", rubbing insects on its feathers possibly to apply liquids such as formic acid secreted by the insects.

Vocals
The grackle's song is particularly harsh, especially when these birds, in a flock, are calling. Songs vary from year-round chewink chewink to a more complex breeding season ooo whew, whew, whew, whew, whew call that gets faster and faster and ends with a loud crewhewwhew! It also occasionally sounds like a power line buzzing. The grackle can also mimic the sounds of other birds or even humans, though not as precisely as the mockingbird, which is known to share its habitat in the Southeastern United States.

Breeding
In the breeding season, males tip their heads back and fluff up feathers to display and keep other males away. This same behavior is used as a defensive posture to attempt to intimidate predators. Male common grackles are less aggressive toward one another, and more cooperative and social, than the larger boat-tailed grackle species.

Relationship with humans
The range of this bird expanded west as forests were cleared. In some areas, it is now considered a pest by farmers because of its large numbers and fondness for grain. Despite a currently robust population, a recent study by the National Audubon Society of data from the Christmas Bird Count indicated that populations had declined by 61% to a population of 73 million from historic highs of over 190 million birds. As a result, it is now classified by the IUCN as Near Threatened.

Unlike many birds, the common grackle benefits from the expansion of human populations due to its resourceful and opportunistic nature. Common grackles are considered to be a serious threat to crops by some, and are notoriously difficult to control; this usually requires the use of hawks or similar large birds of prey.

Proposed magnetoreceptivity
Though the exact mechanism is poorly understood, several studies have examined the ability of the common grackle to interpret the Earth's magnetic field—or in this case, the variability of it. The common grackle (like most of its Quiscalus relatives) has been found to be attuned to a dynamic magnetic field to a scientifically significant degree.

Book

 * Peer, B. D., and E. K. Bollinger. 1997. Common Grackle (Quiscalus quiscula). In The Birds of North America, No. 271 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.

Thesis

 * Eyer LE. Ph.D. (1954). A LIFE-HISTORY STUDY OF THE BRONZED GRACKLE, QUISCALUS QUISCULA VERSICOLOR (VIELLOT). Michigan State University, United States, Michigan.
 * Ficken RW. Ph.D. (1960). BEHAVIOR OF THE COMMON GRACKLE, QUISCALUS QUISCULA (LINNAEUS). Cornell University, United States, New York.
 * Howe HF, 2nd. Ph.D. (1977). ASPECTS OF PARENTAL INVESTMENT AND SEX-RATIO ADJUSTMENT IN THE COMMON GRACKLE. University of Michigan, United States, Michigan.
 * Huntington CE. Ph.D. (1952). THE SUBSPECIES OF THE PURPLE GRACKLE QUISCALUS QUISCULA. Yale University, United States, Connecticut.
 * Maccarone AD. Ph.D. (1985). USE OF FORAGING SUBSTRATES BY STARLINGS AND COMMON GRACKLES IN RELATION TO FOOD AVAILABILITY (BEHAVIORAL, COMMUNAL ROOSTING, NEW JERSEY). Rutgers The State University of New Jersey - Newark, United States, New Jersey.
 * Maxwell GR, II. Ph.D. (1965). LIFE HISTORY OF THE COMMON GRACKLE, QUISCALUS QUISCULA (LINNAEUS). The Ohio State University, United States, Ohio.
 * Stepney PHR. Ph.D. (1979). COMPETITIVE AND ECOLOGICAL OVERLAP BETWEEN BREWER'S BLACKBIRD AND THE COMMON GRACKLE, WITH CONSIDERATION OF ASSOCIATED FORAGING SPECIES. University of Toronto (Canada), Canada.
 * Walley WW. Ph.D. (1965). THE ABSORPTION, METABOLISM, AND ELIMINATION OF DDT IN THE COMMON GRACKLE,QUISCALUS QUISCULA. Mississippi State University, United States, Mississippi.
 * Welker GW. Ph.D. (1962). HELMINTH PARASITES OF THE COMMON GRACKLE QUISCALUS QUISCULA VERSICOLOR VIEILLOT IN INDIANA. The Ohio State University, United States, Ohio.
 * Yang SY. Ph.D. (1968). HYBRIDIZATION IN THE GRACKLE QUISCALUS QUISCULA IN LOUISIANA. The University of Texas at Austin, United States, Texas.

Articles
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 * Bartel KE. (1971). Common Grackle Nest Banding Down in 1971. Inland Bird Banding News. vol 43, no 4. pp. 102–106.
 * Bouvier JM. (1974). The Occupation of an American Robin Nest by a Common Grackle. Canadian Field Naturalist. vol 88, no 4. pp. 483–484.
 * Brackbill H. (1976). Mourning Dove Common Grackle Cleaning Bills. Wilson Bulletin. vol 88, no 4.
 * Bradley JE & Dronen NOJ. (1979). Some Helminth Parasites of the Common Grackle Quiscalus-Quiscula of Southern Texas USA. Proceedings of the Helminthological Society of Washington. vol 46, no 1. pp. 149–150.
 * Brian DP, Homan HJ & Spencer GS. (2001). Infrequent cowbird parasitism in common grackles revisited: New records from the Northern Great Plains. The Wilson Bulletin. vol 113, no 1. p. 90.
 * Buck OD, Cooper CL & Crites JL. (1975). HELMINTH PARASITES OF COMMON GRACKLE (QUISCALUS-QUISCULA-VERSICOLOR) IN CENTRAL OHIO. Journal of Parasitology. vol 61, no 2. pp. 380–380.
 * Buck OD, Cooper CL & Crites JL. (1975). Helminth Parasites of the Common Grackle Quiscalus-Quiscula-Versicolor in Central Ohio. Journal of Parasitology. vol 61, no 2.
 * Caccamise DF, Lyon LA & Fischl J. (1983). Seasonal Patterns in Roosting Flocks of Starlings Sturnus-Vulgaris and Common Grackles Quiscalus-Quiscula. Condor. vol 85, no 4. pp. 474–481.
 * Campbell RW & Sirk GP. (1969). Common Grackle Sighted at Vancouver British-Columbia. Murrelet. vol 50, no 3.
 * Clark CC, Clark L & Clark L. (1990). "Anting" Behavior by Common Grackles and European Starlings. The Wilson Bulletin. vol 102, no 1. p. 167.
 * Clayton DH & Vernon JG. (1993). Common grackle anting with lime fruit and its effect on ectoparasites. Auk. vol 110, no 4. pp. 951–952.
 * Cooper CL & Crites JL. (1974). Helminth Parasites of the Common Grackle Quiscalus-Quiscula-Versicolor from South Bass Island Ohio USA. Proceedings of the Helminthological Society of Washington. vol 41, no 2. pp. 233–237.
 * Cooper CL, Madden JE & Crites JL. (1975). Arthropod Parasites of the Common Grackle in Ohio USA. Journal of Medical Entomology. vol 12, no 2.
 * Davidson AH. (1994). Common grackle predation on adult Passerines. Wilson Bulletin. vol 106, no 1. pp. 174–175.
 * Dubois CA. (1969). Grackle Anting with a Mothball Quiscalus-Quiscula. Auk. vol 86, no 1.
 * Duszynski DW & Box ED. (1978). The Opossum Didelphis-Virginiana as a Host for Sarcocystis-Debonei from Cowbirds Molothrus-Ater and Grackles Cassidix-Mexicanus Quiscalus-Quiscula. Journal of Parasitology. vol 64, no 2. pp. 326–329.
 * Elder DH. (2004). Common grackle anting with moth ball. Ontario Birds. vol 22, no 2. pp. 97–98.
 * Erskine AJ. (1971). Some New Perspectives on the Breeding Ecology of Common Grackles Quiscalus-Quiscula. Wilson Bulletin. vol 83, no 4. pp. 352–370.
 * Farris J, Fleming M & Smith K. (1977). Helminths of the Common Grackle Quiscalus-Quiscula in Faulkner County Arkansas USA. Arkansas Academy of Science Proceedings. vol 31, no 11.
 * Fisk EJ. (1970). Common Grackle Kills Cedar Waxwing in Air. Wilson Bulletin. vol 82, no 4.
 * Granath WOJ. (1981). Eufilaria-Hibleri New-Species Nematoda Filarioidea from the Common Grackle Quiscalus-Quiscula-Versicolor. Proceedings of the Helminthological Society of Washington. vol 48, no 1. pp. 17–23.
 * Gray DA & Hagelin JC. (1996). Song repertoires and sensory exploitation: Reconsidering the case of the common grackle. Animal Behaviour. vol 52, no 4. pp. 795–800.
 * Helleiner FM. (1972). Common Grackle at Rankin Inlet Keewatin District. Canadian Field Naturalist. vol 86, no 1.
 * Hester RL, Rank RG & Johnson AA. (1981). Immune Response of the Common Grackle to Filarial Infection of the Brain with Chandlerella-Quiscali. Arkansas Academy of Science Proceedings. vol 35, no 12.
 * Hickman S. (1981). Evidence for Aerodynamic Advantages of Tail Keeling in the Common Grackle Quiscalus-Quiscula. Wilson Bulletin. vol 93, no 4. pp. 500–505.
 * Homan HJ, Linz GM & Bleier WJ. (1994). Effect of crop phenology and habitat on the diet of common grackles (Quiscalus quiscula). American Midland Naturalist. vol 131, no 2. pp. 381–385.
 * Homan HJ, Linz GM, Bleier WJ & Carlson RB. (1996). Colony-site and nest-site use by Common Grackles in North Dakota. The Wilson Bulletin. vol 108, no 1. p. 104.
 * Howe HF. (1976). Egg Size Hatching Asynchrony Sex and Brood Reduction in the Common Grackle. Ecology. vol 57, no 6. pp. 1195–1207.
 * Howe HF. (1977). Sex Ratio Adjustment in the Common Grackle. Science. vol 198, no 4318. pp. 744–746.
 * Howe HF. (1978). Initial Investment Clutch Size and Brood Reduction in the Common Grackle Quiscalus-Quiscula. Ecology. vol 59, no 6. pp. 1109–1122.
 * Howe HF. (1979). Evolutionary Aspects of Parental Care in the Common Grackle Quiscalus-Quiscula. Evolution. vol 33, no 1 PART 1. pp. 41–51.
 * Huizinga HW & Granath WOJ. (1984). Seasonal Prevalence of Chandlerella-Quiscali Onchocercidae Filarioidea in Brain of the Common Grackle Quiscalus-Quiscula-Versicolor. Proceedings of the Helminthological Society of Washington. vol 51, no 2. pp. 191–195.
 * Jackson J. (1985). The Dunking Habit of Common Grackles Quiscalus-Quiscula Insight Learning or Innate Behavior?. American Birds. vol 39, no 3. pp. 261–262.
 * Kloek GP & Casler CL. (1972). The Lung and Air Sac System of the Common Grackle. Auk. vol 89, no 4. pp. 817–825.
 * Laporte P. (1974 ). Common Grackle Kills a Barn Swallow. Wilson Bulletin. vol 86, p. 4.
 * Larue CT & Ellis DH. (1992). The Common Grackle in Arizona First Specimen Record and Notes on Occurrence. Western Birds. vol 23, no 2. pp. 84–86.
 * Lenington S & Scola R. (1982). Competition between Red-Winged Blackbirds Agelaius-Phoeniceus and Common Grackles Quiscalus-Quiscula. Wilson Bulletin. vol 94, no 1. pp. 90–93.
 * Maxwell GR, II. (1970). Pair Formation Nest Building and Egg Laying of the Common Grackle in Northern Ohio. Ohio Journal of Science. vol 70, no 5. pp. 284–291.
 * Maxwell GR, II, Nocilly JM & Shearer RI. (1976). Observations at a Cavity Nest of the Common Grackle and an Analysis of Grackle Nest Sites. Wilson Bulletin. vol 88, no 3. pp. 505–507.
 * Maxwell GR, II & Putnam LS. (1972). Incubation Care of Young and Nest Success of the Common Grackle Quiscalus-Quiscula in Northern Ohio. Auk. vol 89, no 2. pp. 349–359.
 * Moore WS & Dolbeer RA. (1989). The Use of Banding Recovery Data to Estimate Dispersal Rates and Gene Flow in Avian Species Case Studies in the Red-Winged Blackbird and Common Grackle. Condor. vol 91, no 2. pp. 242–253.
 * Parkes KC. (1999). Head color in bronzed Common Grackles, Quiscalus quiscula versicolor. Western Birds. vol 30, no 3.
 * Peer BD & Bollinger EK. (1997). Explanations for the infrequent Cowbird parasitism on Common Grackles. The Condor. vol 99, no 1. p. 151.
 * Pitts D. (1974). Nesting Failure in a Common Grackle Colony. Migrant. vol 45, no 3. pp. 71–72.
 * Prescott KW. (1971). Severe Foot Pox in Common Grackle and Red-Winged Blackbirds. Ontario Bird Banding. vol 7, no 2. pp. 54–55.
 * Prescott KW. (1972). Severe Foot Pox in Common Grackle and Red-Winged Blackbirds. Ontario Bird Banding. vol 8, no 2. pp. 36–37.
 * Prud Homme-Cyr J, McNeil R & Cyr A. (1976). 1st Quebec Canada Record of Quiscalus-Quiscula-Stonei New-Record the Purple Race of the Common Grackle. Canadian Field Naturalist. vol 90, no 2.
 * Rod JP. (1971). Abnormal Bill in Common Grackle. Iowa Bird Life. vol 41, no 2. pp. 60–61.
 * Ryff AJ. (1974). Predatory Behavior of the Common Grackle. Jack Pine Warbler. vol 52, no 4. pp. 193–194.
 * Snelling JC. (1968). Overlap in Feeding Habits of Redwinged Blackbirds and Common Grackles Nesting in a Cattail-M Marsh Diet Insects Human Interference Quiscalus-Quiscula Agelaius-Phoeniceus. Auk. vol 85, no 4. pp. 560–585.
 * Spero VM & Pitts TD. (1984). Use of Wood Duck Nest Boxes by Common Grackles Quiscalus-Quiscula. Journal of Field Ornithology. vol 55, no 4. pp. 482–483.
 * Stanley JG & Rabalais FC. (1971). Helminth Parasites of the Red-Winged Blackbird Agelaius-Phoeniceus and Common Grackle Quiscalus-Quiscula in Northwestern Ohio. Ohio Journal of Science. vol 71, no 5. pp. 302–303.
 * Summers SD. (1977). A Common Grackle Record for Oregon USA. Western Birds. vol 8, no 4.
 * Twedt DJ. (1984). Pellet Casting by Common Grackles Quiscalus-Quiscula. Wilson Bulletin. vol 96, no 3. pp. 470–471.
 * West GC, Funke ERR & Hart JS. (1968). Power Spectral Density and Probability Analysis of Inst Electro Myograms in Shivering Birds Grosbeak Grackle Hesperiphona-Vespertina Quiscalus-Quiscula. Canadian Journal of Physiology & Pharmacology. vol 46, no 5. pp. 703–706.
 * Zink RM, Rootes WL & Dittmann DL. (1991). Mitochondrial DNA Variation Population Structure and Evolution of the Common Grackle Quiscalus-Quiscula. Condor. vol 93, no 2. pp. 318–329.