One of the most widespread and commonly observed birds of prey in North America, the Red-tailed Hawk (hereafter Red-tail) occupies a broad range of habitats from central Alaska south to Venezuela and east to the Virgin Islands. Breeding behavior, summer food habits, and habitat use have been well documented in many of these regions, but the taxonomic status of some populations remains unclear. The species varies greatly across its range, with up to 16 subspecies recognized by various authorities. Races are usually distinguished by ventral coloration, tail markings, and/or size, but there is no clear geographic trend in any of these characters. Some populations are polymorphic in ventral coloration (i.e., polychromatic), ranging from nearly white to nearly black, and extensive inter-gradation among adjacent subspecies complicates taxonomic relationships. Migration is diurnal, with the extent of migration varying annually depending on weather, especially snow cover. Most migratory movements are < 1500 km, and migrants rarely make water crossings > 25 km. In northernmost populations most individuals migrate south, while those breeding in the southern U.S. and n. Mexico are year-round residents.
Generally monogamous, this species initiates courtship and maintains the pair bond with spectacular aerial maneuvers performed by both members of the pair. Territories are vigorously defended at least during the breeding season, and may be defended year-round by sedentary birds and where overwintering density is high. Territory size varies with habitat and food availability but typically ranges from about 1.25 km2 to more than 2.5 km2; minimum reported inter-nest distance is 0.32 km. At least in sedentary birds, mates stay paired throughout the year. In interior North America, first eggs are laid in mid-late March, but eggs are known as early as December in the tropics. Clutch size is typically 2-3, and incubation lasts about 28 days. Young leave the nest 42-46 days after hatching, but may remain associated with parents up to six months longer.
Throughout its range, this hawk typically inhabits open areas interspersed with patches of trees or structurally similar features. However, Red-tails also nest in high densities in closed-canopy rain and cloud forests in tropical regions. The species is primarily a sit-and-wait predator and generally requires elevated perch sites for hunting. Where it inhabits closed-canopy tropical forests, however, the Red-tail dives on prey from the air far above the canopy. It may also catch bats and other, highly concentrated, flying prey in the air. Occasionally, members of this species capture insects and other prey on foot. The species' diet includes a wide variety of small to medium-sized mammals, birds, reptiles, amphibians, arthropods, and fresh carrion.
This is a common hawk. The global population of 2,000,000 or more is considered stable or slightly increasing, although numbers may be declining slightly in the mixed-woodland plains of far eastern Canada. Populations increased through much of North America during the mid-to-late 20th century, apparently in response to the widespread establishment of open, wooded parkland in place of grassland or dense forest. This species is tolerant of exurban development and agricultural development as long as food is available and the converted landscape includes adequate open space and perch sites for hunting and tall trees or other structures for nesting. Some individuals successfully breed in large, urban environments.
Most information on life history and ecology for this species comes from studies in interior North America of breeding populations (e.g., Fitch et al. 1946b, Craighead et al. 1969, Orians and Kuhlman 1956, Luttich et al. 1970, Luttich et al. 1971, Gates 1972, Johnson 1975d, Mader 1978, Petersen 1979a, Kirkley and Springer 1980, Stout et al. 1998, Stout et al. 2006a) and wintering populations (e.g., Craighead et al. 1969, Petersen 1979a, Preston 1980, Bildstein 1987a, Preston 1990, Garner and Bednarz 2000, Leyhe and Ritchison 2004), but important contributions from Puerto Rico (e.g., Snyder et al. 1987c, Santana and Temple 1988, Boal et al. 2003) have expanded our understanding of how this species adapts to a wide array of habitats across its range. Life history and ecology in the tropics outside of Puerto Rico remains poorly documented, however. The Red-tailed Hawk provides a model for a highly-adaptable, generalist predator, and ongoing studies across its range should provide important insights into how some species are better able than others to exploit varied conditions and persist in rapidly changing environments.