Introduction

The Great-tailed Grackle is a large, sexually dimorphic, widely distributed blackbird. The male is glossy black, with purple iridescence; a long, keel-shaped tail; massive bill; and yellow eyes. Flamboyant in its behavior as well as its plumage, the male has a large and varied vocal repertoire and elaborate courtship and territorial displays. The female, about half the size of the male, is dark brown and has a smaller, keel-shaped tail and yellow eyes.

During the twentieth century, the Great-tailed Grackle experienced rapid, large-scale expansion of its North American range. In 1900, the northern limits of its range barely extended into Texas; by the end of the century, it had nested in at least 14 states and was reported in 21 states and 3 Canadian provinces. This explosive growth occurred mainly after 1960 and coincided with human-induced habitat changes such as irrigation and urbanization.

The Great-tailed Grackle was considered conspecific with the Boat-tailed Grackle (Quiscalus major) as late as 1957, but the 2 species are now thought to be reproductively isolated. While the Boat-tailed Grackle breeds in open marsh in coastal areas, the Great-tailed Grackle prefers drier coastal habitats and is typically found in areas with scattered trees near standing water. It nests high in large trees, as well as in marsh vegetation. Inland, the Great-tailed Grackle is more frequently found in prairies, agricultural areas, and towns, while the Boat-tailed Grackle is more likely to nest in marshy areas. The Common Grackle (Quiscalus quiscula) occurs in many of the same habitats as the Great-tailed Grackle, including marshes and cities, but uses open woodland and forest edge more readily.

The Great-tailed Grackle forages in open, grassy areas such as grasslands, pastures, and lawns. It is well adapted to lawns, trees, and dumpsters in cities. Its diet is varied and includes arthropods, small vertebrates, plant matter, and garbage. Although there is considerable overlap in the distribution of the 3 species, the Common Grackle occurs throughout the eastern United States and Canada, the Great-tailed Grackle is found in the Midwest and western United States, and the Boat-tailed Grackle is confined to Florida and coastal areas of the Gulf states and the eastern United States. Like the Great-tailed Grackle, the Common Grackle expanded its range to the west during the twentieth century.

The social mating system of the Great-tailed Grackle is polygynous, and individuals of both sexes are frequently nonfaithful to their social mates. The male defends a small territory, comprising 1 to several trees, in which females nest. Only adult males acquire territories, and most territorial males are at least 3 years old. In contrast, females usually breed in their second year. Social bonds are ephemeral, and females may switch nesting trees and social mates within or between breeding seasons. The male defends nestlings and fledglings hatched in his territory from potential predators, but otherwise all parental care is provided by the female. Fewer male than female nestlings survive, and adult male survival may be lower than adult female survival, resulting in a female-biased adult sex ratio.

The impressive range expansion of this species presents an instructive contrast to the numerous species that have been adversely affected by human activities. Its great success and its role as a human commensal have made it an agricultural pest and an annoyance to many urbanites, but they have also made it a convenient subject for study. Its behavior is well studied, particularly in Texas (Selander and Giller 1961; Bailey and Griffin 1969; Kok 1970, 1971; Johnson et al. 2000, Peer and Sealy 2000), and several recent phylogenetic studies are available (Avise and Zink 1988, Freeman and Zink 1995, Johnson and Lanyon 1999, Lanyon and Omland 1999). Literature also exists on its range expansion (review in Dinsmore and Dinsmore 1993; see other references in Distribution: historical changes, below) and on methods of controlling the species (West and Dunks 1969; Rappole et al. 1989a, 1989b; Tipton et al. 1989a, 1989b; Knittle et al. 1990).