Great-tailed Grackle

The great-tailed grackle (Quiscalus mexicanus) is a large, long-legged blackbird of the family Icteridae, native to the Americas and strongly sexually dimorphic. Adult males are roughly 43–46 cm long and weigh about 190–250 g, whereas females are only around 33–38 cm and 90–140 g.

Males are glossy black with blue, purple or green iridescence and an exceptionally long, keel-shaped tail that can be spread or folded in different postures. Females are much smaller and brown, with darker wings and tail and a paler throat and breast. Both sexes have pale yellow eyes as adults. The long legs, strong feet and heavy bill are well suited to ground foraging, probing and handling a wide variety of foods.

Eight subspecies are generally recognised, differing mainly in size, bill shape and female plumage across the species’ extensive range.

Great-tailed grackles thrive in open and semi-open habitats, especially where water, short vegetation and human activity occur together. Wetlands, marsh edges, irrigated fields, pastures, farmland, parks, shopping areas, roadsides and urban lawns are all commonly used.

Over the last century the species expanded dramatically northward from Mexico and the southwestern United States. Irrigation, reservoirs, agriculture, planted trees and urban development created new feeding and roosting opportunities across arid and formerly unsuitable landscapes. The species is now widespread through much of the western and central United States and continues to appear beyond its former range.

The great-tailed grackle is an opportunistic omnivore. It eats insects and other invertebrates, grain, seeds, fruit, small fish, amphibians, reptiles, eggs, nestlings and human food waste. Diet changes strongly with local availability.

Most feeding takes place on the ground, where birds walk through lawns, shorelines and fields while scanning, probing and turning over objects. They also forage in shallow water, follow agricultural activity that exposes prey and exploit rubbish bins, parking lots and outdoor eating areas. This flexibility is a major reason the species succeeds in heavily modified environments.

Outside breeding, great-tailed grackles can be highly social. Large communal roosts may contain hundreds or thousands of birds, often in dense trees, reedbeds or urban vegetation. Birds may travel considerable distances between feeding areas and these regular night roosts.

Flocks contain strong dominance relationships, especially around concentrated food. Males use body size, raised plumage, tail posture and direct aggression in disputes, while females also compete for food and nesting positions.

During breeding, males defend territories in which they display to females, and several females may nest within or around the territory of one successful male.

Great-tailed grackles are exceptionally vocal. Their repertoire includes whistles, clicks, rattles, nasal notes, harsh mechanical sounds and long, complex male display sequences. One characteristic call is often rendered as a rising kreee or chack, but the full repertoire is far more varied than a single call suggests.

Males use conspicuous calls together with postures and feather displays around breeding territories, while flock members use shorter calls to maintain contact and react to threats. The variety of sounds is especially noticeable around communal roosts and breeding colonies, where many birds call at once.

Great-tailed grackles have become a useful model for studying how wild animals adapt their behaviour when circumstances change. In reversal-learning experiments, birds learned to abandon a previously rewarded choice when the reward switched, and repeated reversals showed that individuals could improve at adjusting to changing rules.

Experiments published in 2023 found that behavioural flexibility could itself be increased through training, and that this improvement carried over into a new context together with greater innovativeness. Later work in 2024 examined how the birds learned across repeated reversals. The results show that at least part of the species' flexibility is plastic rather than a completely fixed individual trait, which may help explain its success in rapidly changing human-dominated environments.

Communal night roosts are a conspicuous part of the species’ ecology. In urban areas birds may repeatedly use the same groups of trees or reedbeds, arriving in successive flocks near sunset and dispersing again around dawn. These sites can gather birds that spent the day feeding over a much wider area.

Large roosts place birds in close contact and may reduce individual predation risk, but they also create noise, droppings and conflicts with people where thousands of birds gather in towns.

Great-tailed grackles repeatedly return to familiar roosts and appear to use several kinds of environmental information rather than relying on one fixed cue. Visual landmarks can form part of this navigation through complex landscapes.

Great-tailed grackles are polygynous. Males establish and display within breeding territories, and a successful male may mate with several females nesting nearby. Females choose the nest site, build the nest, incubate the eggs and provide nearly all care of the chicks.

The nest is a deep cup woven from grasses, weeds, stems and other fibres, often reinforced with mud and lined with softer material. It is usually attached to reeds, shrubs or trees, frequently above water or in dense vegetation. Human materials such as string, paper or plastic may also be incorporated.

Clutches usually contain 3–4 eggs, with 1–5 recorded. Incubation lasts about 13–14 days. Young normally remain in the nest for about 20–23 days before fledging and continue to depend on the female afterwards.

Breeding timing varies widely with latitude and rainfall. Nesting can begin early in warm southern populations but is concentrated in spring and summer farther north.

The great-tailed grackle is classified as least concern on the IUCN Red List. Its range and numbers increased strongly during the twentieth century as the species colonised new agricultural and urban habitats, and the overall population trend remains increasing.

Local control sometimes occurs where large roosts create conflicts, but the species remains widespread and successful across much of its range.