The Northern Goshawk, Accipiter gentilis, is a medium-large bird of prey in the family Accipitridae, which also includes other diurnal raptors, such as eagles, buzzards and harriers.
It is a widespread species that inhabits the temperate parts of the northern hemisphere. In Europe and North America, where there is only one goshawk, it is often referred to (officially and unofficially, respectively) as simply the "Goshawk". 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 in September and October.
This species was first described by Linnaeus in his Systema naturae in 1758 under its current scientific name.
The Northern Goshawk appears on the flag of the Azores. The archipelago of the Azores, Portugal, takes its name from the Portuguese language word for goshawk, (açor), because the explorers who discovered the archipelago thought the birds of prey they saw there were goshawks; later it was found that these birds were kites or Common Buzzards (Buteo buteo rothschildi).
The Northern Goshawk is the largest member of the genus Accipiter. It is a raptor with short, broad wings and a long tail, both adaptations to manoeuvring through trees in the forests it lives and nests in. Across most of the species's range, it is blue-grey above and barred grey or white below, but Asian subspecies in particular range from nearly white overall to nearly black above. Juveniles and adults have a barred tail, with dark brown or black barring. Adults always have a white eye stripe. In North America, juveniles have pale-yellow eyes, and adults develop dark red eyes usually after their second year, although nutrition and genetics may effect eye color as well. In Europe and Asia, juveniles also have pale-yellow eyes, however adults develop orange-colored eyes. The Northern Goshawk, like all accipiters, exhibits sexual dimorphism, where females are significantly larger than males. Males, being able 10-25% smaller in body are size, are 46–57 cm (18–22 in) long with a 89–105 cm (35–41 in) wingspan. The female is much larger, 58–64 cm (23–25 in) long with a 108–127 cm (43–50 in) wingspan. Males of the smaller races can weigh as little as 515 grams (18.2 oz), whereas females of the larger races can weigh as much as 2.2 kg (4.9 lb). Females are often 30-60% heavier than their mates. The juvenile is brown above and barred brown below. The flight is a characteristic "flap flap, glide", but is sometimes seen soaring in migration, and is capable of considerable, sustained, horizontal speed in pursuit of prey. Goshawks are sometimes confused with gyrfalcons especially when observed in high speed pursuit, with their wingtips drawn backward in a falcon-like profile.
In Eurasia, the male is sometimes confused with a female Sparrowhawk, but is larger, much bulkier and has relatively longer wings. In North America, juveniles are sometimes confused with the smaller Cooper's Hawk, however the juvenile goshawk displays a heavier, vertical streaking pattern on their chest and abdomen and sometimes appears to have a shorter tail due to its much larger and broader body. Although there appears to be a size overlap between small male goshawks and large female Cooper's Hawks, morphometric measurements (wing and tail length) of both species demonstrate no such overlap, although weight overlap can occur due to variation in seasonal condition and food intake at time of weighing. In North America, the Sharp-shinned Hawk is markedly smaller.
This species hunts birds and mammals in a variety of woodland habitats, often utilizing a combination of speed and obstructing cover to ambush birds and mammals. Goshawks are often seen flying along adjoining habitat types, such as the edge of a forest and meadow; flying low and fast hoping to surprise unsuspecting prey. They are usually opportunistic predators, as are most birds of prey. The most important prey species are small mammals and birds found in forest habitats, especially the Ruffed Grouse, snowshoe hare, and red squirrel in North America. Prey species may be quite diverse, including pigeons and doves, pheasants, partridges, gulls, assorted waders, woodpeckers, corvids and passerines (species vary by region). Mammal prey includes rabbits and numerous tree squirrel and ground squirrel species. Waterfowl up to the size of the Mallard are sometimes preyed on. Prey is often smaller than the hunting hawk, but these birds will also occasionally kill much larger animals, up to the size of jack rabbits twice their weight. The Goshawk is likely a significant predator of other raptors, known prey including honey-buzzards, owls, smaller Accipiter and the American Kestrel.
In the spring breeding season, Northern Goshawks perform a spectacular "undulating flight display", and this one the best time to see this secretive forest bird. At this time, the surprisingly gull-like call of this bird is sometimes heard. Adults defend their territories fiercely from intruders, including passing humans. It is presumed that their unusually aggressive nest defense is an adaptation to tree-climbing bears species, such as the black bear in North America. Other raptors are also attacked at nest sites, and often cede territory to, or are themselves killed by the aggressive Goshawk. The Northern Goshawk is considered a secretive raptor and rarely observed even in areas where nesting sites are common.
Adults return to their nesting territories by March or April and begin laying eggs in April or May. Territories often encompass a variety of habitats, however the immediate nest area is often found in a mature or old-growth forest. The clutch size is usually 2 to 4, but anywhere from 1 to 5 eggs may be laid. The eggs average 59 × 45 mm (2.3 × 1.8 in) and weigh about 60 g (2.1 oz). The incubation period can range from 28 to 38 days. The young leave the nest after about 35 days and start trying to fly another 10 days later. The young may remain in their parents' territory for up to a year of age.