The Red-tailed hawk, Buteo jamaicensis, is a species of raptor native to much of North America. Its preferred habitats during winter months are upland pasture, grassland, and hardwood forests1. Summer habitats are much the same but focus on upland hardwood forests and grass-covered ecosystems1. Breeding typically takes place on the periphery of these habits among tree-lined edges and other masking vegetation1. On a larger scale, breeding typically takes place in the western United States but can occur in most areas within the bird’s natural range1,2. When breeding in the northern reaches of its range, in northern Alberta for example, red-tails have been known to pick a nest, lay a clutch of eggs, and incubate the eggs in as little as 3 weeks1. The northernmost edge of the red-tails range is central Alaska, and spans south to the northern Bahamas1. Red-tails usually winter south of Canada2. Migration of red-tailed hawks typically involves leaving the northern areas of North America and migrating south2.
Map of Red-tailed Hawk occurrence. (http://www.allaboutbirds.org/guide/PHOTO/LARGE/bute_jama_AllAm_map.gif)
Buteo jamaicensis is a relatively medium sized bird, but large for a raptor. Average wing measurements are 36.9cm per wing, with females measuring 38.8cm per wing1. Average weights range from 710-1550g1. Females are larger than males in all aspects and cannot be distinguished from males aside from size, as plumage is identical for both sexes3,4. The identifying features of B. jamaicensis are dark brown patches of feathers located on the front edge of the wing, spanning the humerus, extending to the radius and ulna. These dark patches are common across all of the various plumage patterns4. There is also, of course, the red tail feathers that occur in the adult basic plumage; while juveniles have striped tails lacking such a distinct colour variation until their first moult, juveniles are often mostly dark with white breasts and mottled white spots4.
A Juvenile Red-tailed Hawk. Observed, 29, Oct 2015 at Nanaimo River Estuary
There are many different variations of plumage depending on what region of North America the observer is in and these different plumage patterns belong to different subspecies4. The common Red-tailed hawk is a mottled brown with white patches, and has a white belly with white underwings. The red tail of the adult is vibrant from either above or below and can be distinguished at moderate distances. There is a dark morph of the hawk in which the underside of the wing is mostly dark brown with a thick white outline4. In the Southwestern United States it is likely that red-tails will display the common colour pattern but instead of a mottled brown with white patches, the back of the bird will be a uniform brown4. The Krider’s subspecies, occurring in the northern Great Plains, differs from the common red tail in that, near the rump, the tail feathers will lose their red and become an almost pale white colour while retaining red tips4. The most striking deviance from the common colour scheme comes from the Harlan’s subspecies. The Harlan’s is a much darker brown and lacks any discernable red on the tail feathers. The dark patch on the edge of the wing extends throughout most of the underwing and has a less brilliant white outline than the common dark morph4. The Harlan’s is mostly mountainous in habitat, preferring the rocky mountains, Alaska, and the Colorado mountain ranges4.
Plumage Patterns of Red-tailed Hawk subspecies. Photos taken from Sibley, 2003 (See reference 4). From left to right: Common Dark Morph, Southwestern, Krider’s, and Harlan’s plumage patterns. Red-tailed hawks are one of the most common raptors identified, as they often perch near, or over top of, roads looking for easy road-kill prey. However their prey is normally taken live5. Prey of red-tails varies widely, depending on where that specific bird is located1. But in general, small mammals, birds, reptiles and amphibians, and invertebrates tend to make up the dietary in-take averaging 68%, 17.5%, 7%, and 3.2% respectively1. Red-tails often hunt in isolation, even when occupying a territory with their mate it has been reported that each will stay ~100m away from each other while hunting1. Hunting is rarely conducted from a perch, instead the red-tail is likely to hunt by soaring over areas containing prey and then stooping to engage their prey. Hunting is not innate in red-tailed hawks, it is learned1. Young birds will often need to gain experience and learn to actively search for prey through soaring, as opposed to the less costly perch hunting method1. Red-tailed hawks are believed to have lifelong mates1. However it is more likely that pairs of mates maintain bonds over long periods of time, as nest reuse would suggest, but can change mates when needed1. Red-tails are territorial regarding productive nests. Females will often engage in more defensive behaviour than males6. It has been suggested that this is resultant form the sexual dimorphism of size between males and females; with females being the larger of the pair. Nest defensive behaviour consists generally of calls and, when the nest tree is intruded upon, diving toward the interloper6. It has been suggested that nest defensive behaviours correlate with the age of the young inhabiting the nest, with calls and dives becoming more frequent as nestling age increases6. Diving is an effective strategy for defense but comes at high risk to the hawk, as a result diving is often reserved for more serious intrusions towards a nest; furthermore diving begins to decrease as the young birds reach fledging age6. The normal scream of a red-tailed hawk is iconic. The sound has been used in countless cowboy and western films and is typically what comes to mind when one thinks of a raptors voice. The normal call, as well as the scream can be heard here https://www.allaboutbirds.org/guide/Red-tailed_Hawk/sounds
References:
- Johnsgard, P.A., (1990) Hawks, Eagles, & Falcons of North America. Smithsonian Institution Press, Washington and London.
- Bildstein, K.L. (2006) Migrating Raptors of the world: Their Ecology & Conservation. Cornell University Press, Ithaca and London.
- Newton, I. (1979) Population Ecology of Raptors. T & AD Poyser Ltd., London http://site.ebrary.com/lib/viu/reader.action?docID=10486600
- Sibley, D.A., (2003) The Sibley field guide to birds of western North America. Random House of Canada Ltd., Toronto.
- Tabaka, C.S., Ullrey, D.E., Sikasrkie, J.G.; et al. (1996) Diet, cast composition, and energy and nutrient intake of red-tailed hawks (Buteo jamaicensis), great horned owls (Bubo virginianus), and turkey vultures (Cathartes aura). Journal of Zoo and Wildlife Medicine. 27, 2, 187-196. http://www.jstor.org.ezproxy.viu.ca/stable/pdf/20095564.pdf?acceptTC=true
- Andersen, D.E. (1990) Nest-Defense Behaviour of Red-tailed Hawks. Condor, 92, 4, 991-997. http://www.jstor.org.ezproxy.viu.ca/stable/pdf/1368735.pdf?acceptTC=true