Goshawk

December 18th, 2011

 

Northern Goshawk

 

Scientific Name: Accipiter gentilis
Alternate Names: Goshawk
Size: Length from head to toe 46-51 cm (male),
53-62 cm (female); wingspan 98-104 cm (male),
105-115 cm (female); weight 677-1014 g (male),
758-1214 g (female)
Type migrant: partial, irruptive

Introduction

The Northern Goshawk is the most widely distributed Accipiter in the world. A denizen of mature forested regions, the species inhabits boreal and temperate forests in North America, Europe, northwestern Africa, continental Asia, and Japan. In North America, goshawks occur in Canada, the northern United States (including much of Alaska), the mountainous western United States, and northwestern Mexico. The largest of the three North American Accipiters, Northern Goshawks are powerful raptors about the size of Red-tailed Hawks. Historically, Northern Goshawks have been prized falconry birds admired for their capacity to take large prey. In 1929, a five-dollar bounty was placed on the goshawk by Pennsylvania Game & Fish in an effort to protect game species that were sometimes preyed upon by goshawks. The bounty greatly increased raptor shooting throughout Pennsylvania, including along the Kittatinny Ridge. Accounts of irruptions of goshawks in the late 1920s, together with raptor shooting at Hawk Mountain, attracted the attention of conservationists, and ultimately led to the founding of Hawk Mountain Sanctuary, the world’s first sanctuary for birds of prey. Goshawks and other North American Accipiters, or “bird-hawks” were among the last raptors to receive legal protection, and it was not until 1972 that all raptors were protected under the Migratory Bird Treaty Act.

Identification

Adult goshawks have black crowns, white eyebrows, and red irises. As adults, Northern Goshawks are gray above and light gray with black horizontal bars and vertical streaks below. Their tails have a series of alternating dark-gray and lightgray bands. Females typically are larger, browner, and have more heavily marked underparts. Juveniles have brown heads, orange irises, and less distinct, whitish eyebrows. From above, juveniles are brown with a fair amount of white mottling. From below, their cream-colored underparts are heavily streaked with brown. The tails of juveniles have a series of wavy, alternating dark-brown and light-brown bands with thin white borders. Like other Accipiters, the goshawk’s typical flight pattern consists of a series of quick wingbeats interspersed with brief bouts of gliding. Compared to the two smaller North American Accipiters, the flight of Northern Goshawks is more direct, and the flapping is slower with deeper wingbeats.

Breeding Habits

Northern Goshawks nest in mature deciduous, mixed-deciduous, and evergreen forests with large trees, open understories, and sparse ground cover. Goshawks usually select the largest trees in an area for nesting, and most nests are placed on a horizontal branch, either in a fork or near the trunk. Nests are constructed of sticks and lined with bark chips, and are up to 91 cm across. Pairs typically maintain one to eight alternate nests in their territory. Although goshawks sometimes use the same nest in successive years, they are more likely to use alternate nests. Prior to and during nest building, one or both birds perform aerial displays to advertise their territory. Nest construction begins at the start of courtship. Females do most of the nest building and generally display more frequently than males. Goshawks are usually silent except when they are courting. While displaying, individuals often call and spread their undertail coverts. Goshawks perform “sky dances,” which involve “high-circling” followed by “slow-flapping” and “undulating flights.” Throughout the course of the “sky dance,” birds lose altitude, and at the end of the display individuals either “high-circle” or dive into the forest. In addition to “sky dancing,” Northern Goshawks also perform the components of the “sky dance” alone. Males sometimes pursue females. With the female generally in the lead and the male following closely behind, the pair typically flies with slow, deep wingbeats and glides with their wings held in a steep dihedral or “V.”

Northern Goshawks are monogamous, and pairs typically lay a single clutch of three to four eggs each year. The incubation period lasts 35 to 38 days and the female does most of the incubating. For nine to fouteen days after the eggs hatch, the female remains at the nest brooding the nestlings. Thereafter, females spend less time brooding during the day, but continue to brood at night until the nestlings are 24 days old, after which they are brooded only during periods of wet and cold weather. Young goshawks fledge when they are 36 to 42 days old, and they become independent four to eight weeks later. Males fledge earlier and become independent sooner than their female siblings. Fledglings remain dependent on their parents and continue to associate with each other while their flight feathers harden and they learn how to hunt. As they become more proficient in flight, fledglings fly toward and intercept their parents as the latter return with prey.

Feeding Habits

Northern Goshawks hunt in both forested and open habitats. Like other Accipiters, goshawks have short, powerful wings and long tails, which together provide maneuverability and quick bursts of speed. Goshawks are primarily a short duration, sit-and-wait hunter, and they typically travel through the forest in a series of short flights that are interspersed with brief periods of perch hunting. The species also hunts on the wing from fast-searching flights. To surprise their prey, goshawks fly along forest edges, and through dense vegetation. They are both aggressive and persistent hunters and in some instances, pursue escaping prey on foot. When breeding, goshawks cache food in order to maintain a ready supply for their young, especially when the nestlings are small and require frequent, small feedings. Cached prey items usually are placed on a branch near the trunk or are wedged between branches.

Goshawks are opportunistic predators whose diets vary considerably depending upon prey availability. In North America, goshawks prey upon many species of birds and mammals, primarily feeding on ground squirrels and tree squirrels, rabbits, hares, large songbirds, and small- to medium-sized gamebirds. Goshawks also take reptiles and insects. Historically the Passenger Pigeon was a frequently taken prey item. In northern parts of its range, the Northern Goshawk depends on Snowshoe Hares and, to a lesser extent, Ruffed Grouse. The cyclic nature of these species affects goshawk movements, and individuals are more likely to migrate in years when populations of these prey species crash. Birds usually are caught by goshawks on the ground, but some are taken in flight as well. Avian prey are plucked prior to being eaten, and goshawks typically have a traditional plucking post within their territory.

Bibiliography and Credits:

“Raptor Life Histories.” Raptor Life Histories. 01 Jan. 2007. Hawk Mountain Sanctuary. 29 June 2009

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