The Short-tailed Hawk is one of the rarest and least-studied birds in the United States. Although restricted as a breeder in this country to peninsular Florida, it is otherwise a widely distributed species, occurring from northern Mexico southward to northern Argentina, Paraguay, and southern Brazil.
Florida's Short-tailed Hawks represent a disjunct population separated by more than 800 km from the nearest population in Mexico. Although the Florida population remains in the state year-round, there is a well-defined seasonal migration to a small wintering range in the southern peninsula and Florida Keys. Short-tailed Hawks disperse north over most of the peninsula for the breeding season, where their behavior and small number make them difficult to detect. Estimates for Florida do not exceed 150 to 200 pairs, or a maximum of 500 individuals.
One of the most intriguing characteristics of the species is that distinctive light and dark color morphs occur sympatrically and interbreed. In the United States, dark birds probably outnumber light birds, whereas in Central and South America, the reverse may be true. The sexes do not differ in plum-age and, although females are larger, they cannot be distinguished by size in the field. Untrue to its name, the Short-tailed Hawk possesses a tail of average length for its body size among its congeners.
This species soars at great heights on flat wings with slightly upturned wing-tips, which makes it easy to dismiss as a vulture. It rarely perches in the open. A hunting Short-tailed Hawk regularly hangs motionless in the wind, scanning the landscape below for small to medium-sized birds. When it dives at prey, it is usually on a dramatically steep trajectory, although often punctuated by a brief midair hold. It usually takes prey from conspicuous perches in trees or shrubs, although some attacks occur near the ground or, less often, in the air.
The Short-tailed Hawk's immediate nesting habitat usually consists of tall, dense, often wet forest. However, year-round foraging habitats span a broad range of plant communities and physical landscapes. These include swamp forest, mixed forest-prairie landscapes, pine savannas, mangroves, coastal marshes and prairies, and pastures and suburban settings with scattered trees and shrubs.
This species always has been rare in Florida. Although there is no evidence of major changes in distribution or abundance over at least the last half-century, no effective population monitoring has been accomplished. Given the very small size of its population, its apparent isolation, and ongoing degradation of its native habitats, it is potentially vulnerable. The Short-tailed Hawk is not currently listed as threatened or endangered at either the state or federal level. Although the species has not been well studied, Ogden ( Ogden 1974 , Ogden 1988 ) described nesting biology and seasonal movements in southern Florida, and distribution in Florida was assessed by Millsap et al. ( Millsap et al. 1989b , Millsap et al. 1996 ). Work on nesting and wintering ecology, migration, and habitat associations began in 1997 (KDM). More study of the Short-tailed Hawk's conservation biology is needed and, at a minimum, currently occupied areas warrant protection.