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Red-shouldered Hawk (Buteo Lineatus)

Biology

The information on Red-shouldered Hawk biology was obtained from The Birds of North America account No. 107 (Crocoll 1994) unless otherwise referenced.

 

Life Cycle and Reproduction

Red-shouldered Hawks are monogamous, and migrants arrive on territory between February and April, depending on the latitude. Courtship, territory establishment and nest building begin shortly after the pairs return. Nest building (or refurbishing) begins before the end of courtship and takes four to five weeks. Both sexes take part in nest building and refurbishing, using dead and live sticks, shreds of bark, mosses, lichens and fresh sprigs of conifer. Nests are usually located below the canopy, more than halfway up the tree in a crotch of the main trunk. Pairs will often reuse the same nest for several years.

Clutch size averages three to four eggs, and pairs have one clutch/year. Nest success and number of fledglings produced varies widely (published estimates: 1.1-2.6 fledglings/nest, with an average of 1.3). Fifty-five percent of nests fledge at least one chick (Szuba and Norman 1990). Potential factors influencing nest productivity include food availability, timing of nesting and possibly parental age. Based on a small number of banding studies, first-year mortality was 0.587 and later years was 0.297. The longevity record for Red-shouldered Hawks is 19 years, 11 months, but average survival of birds banded between 1955 and 1979 was 25.6 months. Most individuals do not breed until they are greater than one year old, but there are records of yearlings breeding with adults.

 

Predation

Potential predators of eggs, young and/or nesting adults include Great Horned Owls, Red-tailed Hawks, Peregrine Falcons (Falco peregrinus), raccoons (Procyon lotor), martens (Martes americana), and fishers (M. pennanti). 

 

Diet

The Red-shouldered Hawk feeds on a wide variety of prey, but small mammals (chipmunks, mice, voles), frogs and snakes comprise the bulk of their diet in most areas. This species hunts diurnally from perches in forest with open understory or along forest edges, especially forest/wetland edges. 

 

Dispersal/Migration

Adult Red-shouldered Hawks apparently occupy the same nesting territory for life. There is little information available on natal philopatry, but four nestlings banded in Wisconsin were later retrapped as breeding adults less than 24 km from their natal territory.

Red-shouldered Hawks breeding in Canada migrate south for the winter. Christmas Bird Count data show some winter records along Lake Erie in southwestern Ontario, but these may be birds that have migrated from more northerly locations. This species also winters irregularly in southern Quebec. Immatures move south from September through December while adults move from October into December. Fall migration peaks in October at banding sites in southern Ontario. Spring migration in Ontario peaks in March (Niagara Peninsula HawkWatch unpublished data). Dates for spring and fall migration in Quebec are reported in David (1996). 

Red-shouldered Hawks migrate along inland ridges and along the coast. Migrants usually fly alone, but may form small flocks of three or more individuals. This species will cross small water bodies (<25 km) but will avoid larger water barriers. During migration, it is associated with woodlands, but is often seen in smaller woodlands or more fragmented landscapes than it frequents during the breeding season. In winter, Red-shouldered Hawks are found in areas near water, such as swamps, marshes and river valleys. Individuals tend to frequent open habitat more often during winter than in the breeding season.

 

Interspecific Interactions

Aggressive territorial interactions are known to occur between Red-tailed Hawks, Great Horned Owls and Red-shouldered Hawks. When nesting, Red-tailed and Red-shouldered Hawks have non-overlapping territories (Craighead and Craighead 1956). Red-tailed Hawks and Great Horned Owls will usurp the previous year’s nesting locations of Red-shouldered Hawks (Bent 1937; Hanna 1973; Campbell 1975).

 

Adaptability

The species is characterized by its shy, secretive nature and in the breeding season is generally seen only in forest interior habitats. They will, however, breed in suburban areas in some regions (Dykstra et al. 2001). The lineatus subspecies appears to avoid areas of human use (Helferty et al. 2002). Raptors, in general, are very susceptible to human disturbance, particularly early in the breeding season (James 1984) and forests with low canopy closure (which likely occur in areas near human habitation) are associated with Red-shouldered Hawk nesting failure in Ontario (Szuba et al. 1991).