Eurasian Sparrowhawk

Appearance

The Eurasian Sparrowhawk is a small bird of prey with short, broad wings and a long tail, both adaptations to manoeuvring through trees. Females can be up to 25% larger than males and weigh up to twice as much.

When females are larger than males, it is known as reverse sexual dimorphism; this is unusual in higher vertebrates but typical in birds of prey, and most marked in birds of prey which hunt birds.

The adult male is 29–34 cm long, with a wingspan of 59–64 cm and a mass of 110–196 g. He has slate-grey upperparts, with finely red-barred underparts, which can look plain orange from a distance; his irides are orange-yellow or orange-red.

The female is much larger at 35–41 cm long, with a wingspan of 67–80 cm, and a mass of 185–342 g. She has dark brown or greyish-brown upperparts, and brown-barred underparts, and bright yellow to orange irides.

The juvenile is warm brown above, with rusty fringes to the upperparts; and coarsely barred or spotted brown below, with pale yellow eyes; its throat has dark streaks and lacks a mesial stripe.

The Eurasian Sparrowhawk's small bill is used for plucking feathers and pulling prey apart, rather than killing or cutting. Its long legs and toes are an adaptation for catching and eating birds.

Distribution

A widespread species throughout the temperate and subtropical parts of the Old World, the Eurasian Sparrowhawk is resident or breeds in an estimated global range of 23,600,000 km2 and had an estimated population of 1.5 million birds in 2009.

Habitat

This species is common in most woodland types in its range and also in more open country with scattered trees. Eurasian Sparrowhawks prefer to hunt woodland edges, but migrant birds can be seen in any habitat.

The increased proportion of medium-aged stands of trees created by modern forestry techniques have benefited the species, according to a Norwegian study. Unlike its larger relative the Northern Goshawk, it can be seen in gardens and in urban areas and will even breed in city parks.

Reproduction

The Eurasian Sparrowhawk breeds in well-grown, extensive areas of woodland, often coniferous or mixed, preferring forest with a structure neither too dense nor too open, to allow a choice of flight paths.

The nest can be located in the fork of a tree, often near the trunk and where two or three branches begin, on a horizontal branch in the lower canopy, or near the top of a tall shrub. If available, conifers are preferred.

A new nest is built every year, generally close to the nest of the previous year, and sometimes using an old Wood Pigeon nest as a base; the male does most of the work. The structure, made of loose twigs up to 60 cm long, has an average diameter of 60 cm. When the eggs are laid, a lining of fine twigs or bark chippings is added.

During the breeding season, the adult male Eurasian Sparrowhawk loses a small amount of weight while feeding his mate before she lays eggs, and also when the young are large and require more food. The weight of the adult female is highest in May, when laying eggs, and lowest in August after the breeding cycle is complete.

Sexual maturity is reached at between 1–3 years. Most Eurasian Sparrowhawks stay on the same territory for one breeding season, though others keep the same one for up to eight years. A change of mate usually triggers the change in territory. Older birds tend to stay in the same territory; failed breeding attempts make a move more likely.

The eggs are pale blue with brown spots and each measure 35–46 x 28–35 mm, and weigh about 22.5 g of which 8% is shell in a healthy egg. Usually a clutch of four or five eggs is laid. The eggs are generally laid in the morning with an interval of 2–3 days between each egg. If a clutch is lost, up to two further eggs may be laid that are smaller than the earlier eggs.

Food

The Eurasian Sparrowhawk is a major predator of smaller woodland birds, though only 10% of its hunting attacks are successful. It hunts by surprise attack, using hedges, tree-belts, copses, orchards and other cover near woodland areas; its choice of habitat is dictated by these requirements. It also makes use of gardens in built-up areas, taking advantage of the prey found there.

It waits, hidden, for birds to come near, then breaks cover and flies out fast and low. A chase may follow, with the hawk even flipping upside-down to grab the victim from below or following it on foot through vegetation. It can "stoop" onto prey from a great height. Ian Newton describes seven modes of hunting used by Eurasian Sparrowhawks:

⤷  Short-stay-perch-hunting
⤷  High soaring and stooping
⤷  Contour-hugging in flight
⤷  Still-hunting
⤷  Low quartering
⤷  Hunting by sound
⤷  Hunting on foot

Predators

Natural predators of the Eurasian Sparrowhawk include the Barn Owl, the Tawny Owl, the Northern Goshawk, the Peregrine Falcon, the Golden Eagle, the Eagle Owl, the Fox, the Stone Marten and the Pine Marten.

Migration

Eurasian Sparrowhawks from colder regions of northern Europe and Asia migrate south for the winter, some to north Africa and India; members of the southern populations are resident or disperse. Juveniles begin their migration earlier than adults and juvenile females move before juvenile males.

Analysis of ringing data collected at Heligoland, Germany, found that males move further and more often than females; of migrating birds ringed at Kaliningrad, Russia, the average distance moved before recovery was 1,328 km for males and 927 km for females.