Species: Accipiter gentilis

Northern Goshawk

Species

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Species of concern in the Puget Sound watershed

Encyclopedia of Puget Sound

A fairly large hawk with a long tail, rounded wing tips, and a conspicuous pale eyebrow; adult has dark crown, blue-gray back, white underparts with dense gray barring, and conspicuous fluffy white undertail coverts; immature is brown above, buffy below, with dense blurry streaking, undertail coverts are dark-streaked, and tail has wavy dark bands bordered with white and a thin white tip; total length is 53-66 cm, with females averaging lager than males (NGS 1983).

Classification

Kingdom

Animalia

Phylum

Craniata

Class

Aves

Order

Falconiformes

Family

Accipitridae

Genus

Accipiter

NatureServe

Source:
ELEMENT_GLOBAL.2.104351

Classification

Other Global Common Names

Gavilán Azor - autour des palombes

Informal Taxonomy

Animals, Vertebrates - Birds - Raptors

Formal Taxonomy

Animalia - Craniata - Aves - Falconiformes - Accipitridae - Accipiter - is questionable (see Banks 1995).

Ecology and Life History

Short General Description

A fairly large hawk; male 55 cm in length with a wingspan of 98-104 cm, female 61 cm in length with a wingspan of 105-115 cm (Squires and Reynolds 1997). Male is brown-gray to slate gray on back, head with black cap and pronounced white supercilary line. Undersides are light gray with fine horizontal vermiculations and fine black vertical streaks. Long, rounded tail, white undertail coverts, dark gray above with 3-5 dark bands and a think, white terminal band (reduced or absent with wear). Female is similar to male but browner on back and more heavily marked on underside, sometimes appearing barred. Feet, cere, toes, legs, and mouth-lining are yellow, eyes are red. Juveniles dark brown to brown-black on back with buff white and cinnamon streaks. Undersides buff white with thick cinnamon to blackish brown streaks on throat. Tail is dark brown with wavy dark-brown bands that are bordered by thin whitish bands, forming a zigzag pattern.

Migration

true - true - false - Generally a permanent resident or conducts only short-distance movements over most of range, but periodically has irruptions of movement out of northern portions of range. Fall migration appears to be influenced by prey availability (Squires and Reynolds 1997). For example, in Yukon Territory, Canada, year-round residents are abundant when snowshoe hares (LEPUS AMERICANUS) are abundant, but scarce in winter when hare population is low (Doyle and Smith 1994). Approximately once per decade, large numbers migrate southward, apparently in response to a decline in prey populations, particularly snowshoe hares and ruffed grouse (BONASA UMBELLUS; Bent 1937, Doyle and Smith 1994, Mueller et al. 1977, Squires and Reynolds 1997). Depending on location and year, fall movements begin in late August through September, peak in late September through mid-November, and typically end in December. Spring movements, which are less pronounced, begin in late February and continue through late May. Movement routes are poorly defined, particularly in the western U.S. In the eastern U.S., migrates along the Great lakes, the Appalachian Mountains and the Atlantic coast (Squires and Reynolds 1997). Some birds make extensive movements; four individuals, banded in Minnesota, were recovered up to 2400 kilometers away in British Columbia (Evans and Rosenfield 1985, cited in Squires and Reynolds 1997; Campbell et al. 1990). Other birds, however, undergo short movements from one elevation to another (Squires and Reynolds 1997).

Non-migrant

true

Locally Migrant

true

Food Comments

Forages during short flights alternated with brief prey searches from perches. Also hunts by flying rapidly along forest edges, across openings, and through dense vegetation. An opportunistic hunter, preys on a wide variety of vertebrates and, occasionally, insects. Prey is taken on the ground, in vegetation, or in the air. Despite their larger size, females do not capture larger or heavier prey than males (Boal and Mannan 1996). Dominant mammalian prey include five species of tree squirrels, four ground squirrels, and lagomorphs. Frequently killed birds include three galliformes, four corvids, six woodpeckers (piciformes) and the American robin (TURDUS MIGRATORIUS; Squires and Reynolds 1997). During the nesting season, the diet can vary with prey availability. For example, as more fledgling passerines become available, they make up a greater portion of the diet (Linden and Wikman 1983, Reynolds and Meslow 1984). Ratio of mammalian prey to avian prey in the diet during the breeding season (in percent): Arizona, 76:24 and 62:38 (Boal and Mannan 1994, Reynolds et al. 1994); Nevada, 67:32 (Younk and Bechard 1994); New York, 39:61 (Grzybowski and Eaton 1976); and Oregon, 42:59 and 45:55 (Bull and Hohmann 1994, Reynolds and Meslow 1984). Nonbreeding season food habits are unknown for North American populations. In Sweden, birds dominate the diet during the nesting season (86 percent of prey), whereas in winter, red squirrels (SCIURUS VULGARIS) comprise the bulk of the diet (79 percent; Widen 1987, cited in Squires and Reynolds 1997).

Reproduction Comments

Usually one clutch produced per year, from late April through early May (Squire and Reynolds 1997); however, some individuals may not breed during cold, wet springs (DeStefano et al. 1994). Egg-laying may begin later at higher elevations and during cold, wet springs (Henny et al. 1985, Younk and Bechard 1994). Clutch is typically two to four eggs, rarely one to five (Squires and Reynolds 1997). Average clutch size of 44 North American clutches is 2.7 eggs (Apfelbaum and Seelbach 1983 cited in Squires and Reynolds 1997). Eggs are laid every two to three days and incubation usually begins after the second egg is laid. Incubation, conducted principally by the female, takes 28-38 days; hatching is asynchronous. Few data regarding hatching success. In Oregon, hatching success in five nests was 81 percent (Reynolds and Wight 1978 cited in Squires and Reynolds 1997). Nest success (percentage of active nests that fledge greater than one young) in North America ranges from 44-94 percent and most populations produce 2-2.8 fledglings per successful nest (summarized in Squires and Reynolds 1997). Egg/nestling mortality has been attributed to exposure to cold and rain and siblicide (Boal and Bacorn 1994, Squires and Reynolds 1997). In northern Wisconsin, nest success dropped from 94 percent to 62 percent due to an increase in predation of nest contents and adult females by fishers. Increased predation by fishers was attributed to an increase in the fisher population and nest exposure due to tree defoliation by forest tent caterpillars (MALACOSOMA DISSTRIA; Erdman et al. 1998). Brooding and feeding of nestlings is performed principally by the female; the male brings food to the nest. The young begin flying at 35-42 days and become independent at about 70 days (Boal 1994, Squires and Reynolds 1997). Maintain one to eight alternate nests within a nest area (Squire and Reynolds 1997). Alternate nests range from 15-2066 meters apart (Reynolds and Wight 1978, cited in Squires and Reynolds 1997; Woodbridge and Detrich 1994). The average distance between nests of nearest neighboring pairs in Arizona was 3 kilometers (range = 1.6-6.4 kilometers; Reynolds et al. 1994). A small percentage (less than 10 percent) of subadults (1-2 years old) are sexually mature; however, most breeding birds are young adults (2-3 years old) or adults (Squires and Reynolds 1997). Nesting by subadults is more frequent in expanding populations and less frequent in stable populations (Reynolds and Wight 1978, cited in Squires and Reynolds 1997).

Ecology Comments

Nesting densities of most western U.S. populations range from 6.6-10.7 pairs per 100 square kilometers (summarized in Squires and Reynolds 1997). The single nesting density estimate for the eastern U.S. is 1.17 pairs per 100 square kilometers (Kimmel and Yahner 1994, cited in Squires and Reynolds 1997). Home ranges during nesting vary from 95-3500 hectares depending on sex and habitat characteristics (Squires and Reynolds 1997). Home ranges of males are typically larger than those of females (Hargis et al. 1994, Keane and Morrison 1994, Kennedy et al. 1994). Exclusive of nesting areas, home ranges of adjacent pairs are not defended and may overlap (Squires and Reynolds 1997). The core area (encompasses nest site) constitutes 32 percent of the home range (Kennedy et al. 1994). Individuals typically enlarge or sometimes shift location of home ranges after breeding (Hargis et al. 1994, Keane and Morrison 1994). Home ranges of non-breeders are poorly known, but may be larger than those of breeders (Squires and Reynolds 1997). In North America, winter home ranges are unknown. In Sweden, winter home-ranges of males and females were similar and averaged 5700 hectares (Widen 1989). In California, 76.5 percent of males and 71.4 percent of females returned to the same nesting area in subsequent years. Males were significantly more likely to return to previously-inhabited territories in consecutive years than females (Detrich and Woodbridge 1994). In Arizona, 80 percent of nest areas examined in two consecutive years were re-used the second year by one or both members of the pair banded the first year (Reynolds et al. 1994). Sixty to 72 percent of adults located in consecutive years retained the mate from the previous year (Detrich and Woodbridge 1994, Reynolds et al. 1994). Dispersal of young is not well documented. Detrich and Woodbridge (1994) recaptured two adult females, banded as nestlings 5-7 years prior, 16 and 24 kilometers from their natal sites. Three females, banded as nestlings and recaptured as breeding adults, moved an average of 21.5 kilometers from their natal sites, and another female, captured as a breeding adult seven years after being banded as a nestling, moved 100 kilometers from its natal site (Squires and Reynolds 1997). Little is known regarding survivorship in the U.S. In Arizona, annual survivorship of male and females more than 1 year old was estimated to be 68.8 percent and 86.6 percent, respectively (Squires and Reynolds 1997). In Yukon, Canada, an observed population decline was attributed to increased mortality of eggs, nestlings, immatures and adults, as well as to dispersal following a precipitous decline in number of snowshoe hares (Doyle and Smith 1994). The maximum lifespan of a wild bird is 11 years (Squires and Reynolds 1997). The sex ratio is 1:1 prior to fledging and among adults (Mueller and Berger 1968, Reynolds et al. 1994).

Length

Weight

1137

Conservation Status

NatureServe Global Status Rank

Global Status Last Reviewed

1999-11-30

Global Status Last Changed

1996-11-22

Distribution

Conservation Status Map

Global Range

H - >2,500,000 square km (greater than 1,000,000 square miles) - H - BREEDING: North America: western and central Alaska to northeastern Manitoba, Labrador, and Newfoundland, south to central California, southern Arizona, eastern foothills of Rockies, central Alberta, southern Manitoba, central Michigan, Pennsylvania, northwestern Connecticut, and in the Appalachians south to West Virginia and Maryland; locally in highlands of Mexico to Jalisco and Guerrero. Eurasia: British Isles, Scandinavia, northern Russia, and northern Siberia south to the Mediterranean, Asia Minor, Iran, the Himalayas, eastern China, and Japan (Squires and Reynolds 1997, AOU 1998). NON-BREEDING: throughout breeding range and irregularly southward (Squires and Reynolds 1997, AOU 1998). In some years there are large flights (irruptions) south beyond the usual wintering range. These excursions are prompted by changing conditions on the northern breeding grounds (Mueller et al. 1977). Recorded occasionally as far south as Arkansas, Louisiana, Kentucky, Alabama, and North Carolina (Adkisson 1990). The three subspecies in the U.S. have the following ranges: 1) ATRICAPILLUS: Alaska, Canada, eastern U.S., and the more northerly mountains of the west. 2) LAINGI: islands off the Canadian Pacific coast. 3) APACHE: southern Arizona, New Mexico, and the mountains of northwestern Mexico (Jones 1979).

Global Range Code

Global Range Description

>2,500,000 square km (greater than 1,000,000 square miles)

ELEMENT_GLOBAL.2.104351