American goshawk

The American goshawk is a species of raptor in the family Accipitridae. It was first described by Alexander Wilson in 1812. The American goshawk was previously considered conspecific with the Eurasian goshawk but was assigned to a separate species in 2023 based on differences in morphology, vocalizations, and genetic divergence. It was formerly placed in the genus Accipiter. It is mainly resident, but birds from colder regions migrate south for the winter. In North America, migratory goshawks are often seen migrating south along mountain ridge tops at nearly any time of the fall depending on latitude.

Distribution

In North America, they are most broadly found in the Western United States, including Alaska, and western Canada. Their breeding range in the western contiguous United States largely consists of the wooded foothills of the Rocky Mountains and many other large mountain ranges from Washington to southern California extending east to central Colorado and westernmost Texas. Somewhat discontinuous breeding populations are found in southeastern Arizona and southwestern New Mexico, thence also somewhat spottily into western Mexico down through Sonora and Chihuahua along the Sierra Madre Occidental as far as Jalisco and Guerrero, their worldwide southern limit as a breeding species.
The goshawk continues east through much of Canada as a native species, but is rarer in most of the Eastern United States, especially the Midwest, where they are not typically found outside the Great Lakes region, where a good-sized breeding population occurs in the northern parts of Minnesota, Illinois, Michigan, and somewhat into Ohio; a very small population persists in the extreme northeast corner of North Dakota. They breed also in mountainous areas of New England, New York, central Pennsylvania, and northwestern New Jersey, sporadically down to extreme northwestern Maryland and northeastern West Virginia. Vagrants have been reported in most of the parts of the United States in which they do not breed.

Habitat

American and Eurasian goshawks can be found in both deciduous and coniferous forests. While the species might show strong regional preferences for certain trees, they seem to have no strong overall preferences nor even a preference between deciduous or coniferous trees despite claims to the contrary. More important than the type of trees are the composition of a given tree stand, which should be tall, old-growth with intermediate to heavy canopy coverage and minimal density undergrowth, both of which are favorable for hunting conditions. Also, goshawks typically require proximity to openings in which to execute additional hunting.
Access to waterways and riparian zones of any kind is not uncommon in goshawk home ranges but seems to not be a requirement. Narrow tree-lined riparian zones in otherwise relatively open habitats can provide suitable wintering habitat in the absence of more extensive woodlands. The American goshawk can be found at almost any altitude, but recently is typically found at high elevations due to a paucity of extensive forests remaining in lowlands across much of its range. Altitudinally, goshawks may live anywhere up to a given mountain range's tree line, which is usually in elevation or less. In winter months, the northernmost or high mountain populations move down to warmer forests with lower elevations, often continuing to avoid detection except while migrating. A majority of goshawks around the world remain sedentary throughout the year.

Description

Similar species

The juvenile plumage of the species may cause some confusion, especially with other juvenile Astur species. Unlike other northern Astur, the adult American and Eurasian goshawk never has a rusty color to its underside barring. Wing beats of American goshawks are deeper, more deliberate, and on average slower than those of the two other North American Asturs.
American goshawks are sometimes mistaken for species even outside of the genus Astur especially as juveniles of each respective species. In North America, four species of buteonine hawk may be confused with them on occasion despite the differing proportions of these hawks, which all have longer wings and shorter tails relative to their size. A species so similar it is sometimes nicknamed the "Mexican goshawk", gray hawk juveniles have contrasting face pattern with bold dusky eye-stripes, dark eyes, barred thighs and a bold white "U" on the uppertail coverts. The roadside hawk is noticeably smaller with paddle-shaped wings, barred lower breast and a buff "U" on undertail coverts in young birds. Somewhat less likely to confuse despite their broader extent of overlap are the red-shouldered hawk which have a narrow white-barred, dark-looking tail, bold white crescents on their primaries and dark wing edges and the broad-winged hawk which also has dark wing edges and a differing tapered wing shape. Even wintering gyrfalcon juveniles have been mistaken for goshawks and vice versa on occasion, especially when observed distantly perched. However, the bulkier, broader headed yet relatively shorter tailed falcon still has many tell-tale falcon characteristics like pointed, longer wings, a brown malar stripe as well as its more extensive barring both above and below.
Juveniles are sometimes confused with the smaller Cooper's hawk, especially juvenile Cooper's hawks. Unlike in Europe with sparrowhawks, Cooper's hawks can have a largish appearance and juveniles may be regularly mistaken for the usually less locally numerous goshawk. However, the juvenile goshawk displays a heavier, vertical streaking pattern on chest and abdomen, with the juvenile Cooper's hawk streaking frequently in a "teardrop" pattern wherein the streaking appears to taper at the top, as opposed to the more even streaking of the goshawk. The goshawk sometimes seems to have a shorter tail relative to its much broader body. Although there appears to be a size overlap between small male goshawks and large female Cooper's hawks, morphometric measurements of both species demonstrate no such overlap, although weight overlap can rarely occur due to variation in seasonal condition and food intake at time of weighing.

Taxonomy

The genus Astur contains nine living species. This group of agile, smallish, forest-dwelling hawks has been in existence for possibly tens of millions of years, probably as an adaptation to the explosive numbers of small birds that began to occupy the world's forest in the last few eras. The harriers are the only group of extant diurnal raptors that seem to bear remotely close relation to this genus, whereas buteonines, Old World kites, sea eagles and chanting-goshawks are much more distantly related and all other modern accipitrids are not directly related.
Within the genus Astur, the American goshawk seems to belong to a superspecies with other larger goshawks from different portions of the world. Eurasian goshawk, found in Eurasia, was previously considered conspecific with American goshawk, formed the species complex "northern goshawk". Meyer's goshawk, found in the South Pacific, has been posited as the most likely to be the closest related living cousin to the northern goshawk, the somewhat puzzling gap in their respective ranges explained by other Palearctic raptors such as Bonelli's eagles and short-toed eagles that have extant isolated tropical island populations and were probably part of the same southwest Pacific radiation that led to the Meyer's goshawk. A presumably older radiation of this group may have occurred in Africa, where it led to both the Henst's goshawk of Madagascar and the black sparrowhawk of the mainland. While the Henst's goshawk quite resembles the northern goshawks, the black sparrowhawk is superficially described as a "sparrowhawk" due to its relatively much longer and finer legs than those of typical goshawks but overall its size and plumage is much more goshawk than sparrowhawk-like.
Genetic studies have indicated that the Cooper's hawk of North America is also fairly closely related to the northern goshawk, having been present in North America before either of the two North American species of Astur. However, the much smaller sharp-shinned hawk, which has similar plumage to the Cooper's hawk and seems to be most closely related to the Eurasian sparrowhawk, appears to have occupied North America the latest of the three North American species of Accipitrinae, despite having the broadest current distribution of any of the American members of Accipitrinae.

Subspecies

A. a. atricapillus – This subspecies occupies a majority of the species' range in North America, excluding some islands of the Pacific Northwest and the southern part of the American Southwest. American goshawks are generally slightly smaller on average than most Eurasian ones, although there are regional differences in size that confirm mildly to Bergmann's rule within this race. Furthermore, sexual dimorphism in size is notably less pronounced in American goshawks than in most Eurasian races. Overall, the wing chord is in males and in females. Size within atricapillus based on body mass seems to be highest in interior Alaska, followed by the Great Lakes, is intermediate in the northwest United States from eastern Washington to the Dakotas as well as in southeast Alaska thence decreasing mildly along the Pacific in Oregon and California and smallest of all within the race in the Great Basin and Colorado Plateau states. Conspicuously, wing size did not correspond to variations in body mass and more southerly goshawks were frequently longer winged than the more massive northerly ones. Male atricapillus goshawk have been found to weigh from and females from. The lightest reported mean weights were from goshawks in northern and central Arizona, weighing a mean of in males and while the highest were from a small sample of Alaskan goshawks which weighed some in males and in females. Almost identical mean weights for goshawks as in Alaska were recorded for goshawks from Alberta as well. This race is typically a blue-gray color above with a boldly contrasting black head and broad white supercilia. American goshawks are often grayish below with fine gray waving barring and, compared to most Eurasian goshawks, rather apparent black shaft streaks which in combination create a vermiculated effect that is all-together messier looking than in most Eurasian birds. From a distance, atricapillus can easily appear solidly all-gray from the front. Due to this, the adult goshawk in America is sometimes called the "gray ghost", a name also somewhat more commonly used for adult male hen harriers. Birds from mainland Alaska tend to be paler overall with more pale flecking than other American goshawks.
A. a. laingi Tavernier, 1940 – This insular race is found on Haida Gwaii and Vancouver Island. This subspecies is slightly smaller than the goshawks found on the mainland and is linearly the smallest race on average in North America. The wing chord of males can range from and that of females is and is on average nearly 5% smaller than those sampled goshawks from the nearby mainland. These goshawks are characteristically darker than mainland goshawks with the black of the crown extending to the interscapulars. The underside is a sootier gray overall.
A. a. apache – The range of this subspecies extends from southern Arizona and New Mexico down throughout the species' range in Mexico. This subspecies has the longest median wing size of any race, running contrary to Bergmann's rule that northern birds should outsize southern ones in widely distributed temperate species. In males the wing chord ranges from while in females it ranges from. However, in terms of body mass, it is only slightly heavier than the goshawks found discontinuously somewhat to the north in the Great Basin and the Colorado Plateau and lighter than the heaviest known American goshawks from Alaska, Alberta and Wisconsin despite exceeding the goshawks from these areas in wing size. The weight of 49 males ranged from, averaging, while that of 88 females from two studies ranged from, averaging. Aside from its overall larger size, apache reportedly averages larger in foot size than most other American goshawks. Birds of this race tend to be darker than other American goshawks aside from the laingi type birds. Due to its shortage of distinct features beyond proportions, this is considered one of the more weakly separated among current separate subspecies, with some authors considering it merely a clinal variation of atricapillus. Even the greater wing size in southern birds follows a trend for the wing chord to increase in size in the south on the contrary to body mass.