Flying Tigers - Northern Goshawks

by: Mark Elderkin
SEASON

The Department of Lands and Forestry' Wildlife Division is asking the forest industry and naturalist groups throughout Nova Scotia to assist with a study on the breeding habitats of the northern goshawk (Accipiter gentile atricapillus). In recent years, eastern populations of migratory Accipiterine hawks, especially the sharp-shinned and Cooper's, have declined from causes not yet fully understood. The status of the larger northern goshawk is more difficult to assess because the extent of migration is any given year is unpredictable. Although the amount of disturbance individual pairs of northern goshawk will tolerate during the breeding season varies, most are extremely sensitive and will desert if bothered by nearby human activity, such as forest harvesting.

The northern goshawk is the largest of the three Accipiterine (from the Latin meaning "hawk-like-bird of prey") hawks that occur in the province. Goshawks are found in forested habitat throughout Canada, depending upon mature forests for nesting. They feed on a variety of larger birds and mammals, such as the northern flicker, ruffed grouse, snowshoe hare, and red squirrel. Normally goshawks overwinter in Nova Scotia, but during severe crashes of preferred prey they may range into the eastern United States. At or near the top of the food chain in forested landscapes, breeding goshawks are ideal indicators of healthy ecosystems.

Although the colouration of immature northern goshawks is nearly identical to that of immature sharp-shinned and Cooper's hawks, the adult plumage is distinctive. Immature goshawks are brown on the back, with creamy white underparts streaked with brown. The distinctive adult colouration is not attained until their second full spring.Adults are pale grey to blue-grey on the back, with blackish grey on the sides and top of the head and distinquishing white "eyebrows." Their underparts are white with grey-black streaks and more numerous, finely vermiculated grey lines. The eyes colour of immature birds is a deep yellow and is vermilion red in adults.

Northern goshawks are monogamous and mate for life. They are territorial and, if left undisturbed, will return year after year to the same general area to breed. Nests are large, bulky, and constructed of coarse sticks and smaller twigs. Clutches of two to four bluish-white eggs are laid during the last weeks of April or in the first week of May. The eggs are incubated by the female for 36 to 41 days. Young begin to hunt on their own about 50 days after hatching and are independent by about 70 days of age. Throughout the nesting period, fresh evergreen sprigs may be added to sanitize the nest. Some researchers have speculated that this behaviour may ward off parasites and biting insects that bother the young. The same nest may be used over several consecutive nesting seasons with only minor repairs, or two or three additional nests may be constructed nearby in the same breeding territory and used in alternate years. R.W. Tufts recorded the tree species used for breeding in 44 separate nesting attempts in Nova Scotia (see table).

Table: Nest Tree Preference In Nova Scotia
Tree Species Number Found
Yellow Birch
12
White Birch
5
Maple
6
Poplar
6
Beech
7
Pine
5
Hemlock
2
Spruce
1

Anyone who knows the location of active goshawk nests should contact Mark Elderkin at the Wildlife Division in Kentville (902-679-6091) or the regional biologist in their area. Some or all of the nests reported wil be visited to document the condition and type of forest. Goshawks tend to be extremely aggressive toward humans around their nests during breeding season, especially when your are present. Therefore, anyone doing nest checks should protect themselves by wearing a heavy jacket and a helmet equipped with a visor. All birds of prey and their nests are protected in Nova Scotia.

Mark Elderkin is a wildlife biologist with the Wildlife Division in Kentville