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Identificazione

Great-tailed grackles are medium-sized birds (larger than starlings and smaller than crows; 38–46 cm (15–18 in) with males weighing 203–265 g (7.2–9.3 oz) and females 115–142 g (4.1–5.0 oz), and both sexes have long tails. Wingspan ranges 18.9–22.8 in (48–58 cm). Males are iridescent black with a purple-blue sheen on the feathers of the head and upper body, while females are brown with darker wings and tail. Adults of both sexes have bright yellow eyes, while juveniles of both sexes have brown eyes and brown plumage like females (except for streaks on the breast). Great-tailed grackles, particularly the adult males, have a keel-shaped tail that they can fold vertically by aligning the two halves.<p>The great-tailed grackle and boat-tailed grackle were considered the same species until genetic analyses distinguished them as two separate species.

Tassonomia

The great-tailed grackle was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it with the crows in the genus Corvus and coined the binomial name Corvus mexicanus. The type locality has been restricted to the region of Veracruz in Mexico. Gmelin's account was based on De Hocitzanatl that had been described by the Spanish naturalist Francisco Hernández de Toledo in his work Rerum medicarum Novae Hispaniae thesaurus, seu, Plantarum animalium mineralium Mexicanorum historia. The work was published in 1651, long after Hernández's death in 1587. "Hocitzanatl" was the name for the bird in a local Mexican language. The bird was also been mentioned in 1770 by the French author Antoine-Joseph Pernety in his work Histoire d'un voyage aux Isles Malouines. The great-tailed grackle is now one of six species placed in the genus Quiscalus that was introduced by Louis Vieillot in 1816.<p>Eight subspecies are recognised:

Nome scientifico

Quiscalus mexicanus

Autorità

(Gmelin, JF, 1788)

Ordine

Passeriformi

Famiglia

Icteridae

Genere

Quiscalus

Areale e habitat

Great-tailed grackles originated from the tropical lowlands of Central and South America, but historical evidence from Bernardino de Sahagún shows that the Aztecs, during the time of the emperor Ahuitzotl, introduced the great-tailed grackle from their homeland in the Mexican Gulf Coast to the Aztec capital of Tenochtitlan in the highland Valley of Mexico, most likely to use their iridescent feathers for decoration. In more recent times, great-tailed grackles expanded their breeding range by over 5,500% by moving north into North America between 1880 and 2000, following urban and agricultural corridors. Their current range stretches from northwestern Venezuela and western Colombia and Ecuador in the south to Minnesota in the north, to Oregon, Idaho, and California in the west, to Florida in the east, with vagrants occurring as far north as southern Canada. Their habitat for foraging is on the ground in clear areas such as pastures, wetlands and mangroves, and chaparral. The grackles' range has expanded with agricultural and urban settings.

Migrazione

Resident species

Comportamento

Great-tailed grackles communally roost in trees or the reeds of wetlands at night and, during the breeding season, they nest in territories using three different mating strategies: 1) territorial males defend their territory on which many females place their nests and raise young, 2) residential males live in the larger colony but do not defend a territory or have mates, and 3) transient males stay for a few days before leaving the colony to likely move on to another colony. Resident and transient males sire a small number of offspring through extra-pair copulations with females on territories. Territorial males are heavier and have longer tails than non-territorial males, and both of these characteristics are associated with having more offspring.<p>Great-tailed grackles can solve The Crow and the Pitcher puzzle - a problem involving a tube that is partially filled with water and a floating, out-of-reach piece of food. The problem is solved by dropping objects into the water to raise the level and bring the food within reach. They are also behaviorally flexible, changing their preferences quickly in response to changes in cognitive tasks.<p>The great-tailed grackle mating season usually begins in early or mid-April. The nest is typically built near the top of a large or medium-sized tree, using materials such as woven grass and twigs, as well as some man-made materials. Females usually lay around 4 to 7 eggs. Incubation is usually around 13 to 14 days and their young usually leave the nest 12 to 17 days after hatching; the parents continue to feed their young several weeks after they have left the nest until they reach maturity. Eggs are bright blue to pale bluish gray in color, marked with swirls and splotches that range from dark brown to black.<p>Great-tailed grackles are noted for their diverse foraging habits. They extract larvae and insects from grassy areas; eat lizards, nestlings, and eggs; forage in freshly plowed land; remove parasites from cattle, and eat fruits (e.g., bananas, berries) and grains (e.g., maize, corn on the cob by opening the husks). They turn over objects to search for food underneath, including crustaceans, insects, and worms, they hunt tadpoles and fish by wading into shallow water, and although they do not swim, they catch fish by flying close to the water's surface, and are even reported to dive a few inches into the water to retrieve a fish. They are also known to pick dead insects off the license plates of parked cars, and kill barn swallows while flying.

Conservazione

Tendenza della popolazione

stable