Eurasian sparrowhawk

The Eurasian sparrowhawk (''Accipiter nisus''), also known as the northern sparrowhawk or simply the sparrowhawk, is a small bird of prey in the family Accipitridae. Adult male Eurasian sparrowhawks have bluish grey upperparts and orange-barred underparts; females and juveniles are brown above with brown barring below. The female is up to 25% larger than the male – one of the greatest size differences between the sexes in any bird species. Though it is a predator which specialises in catching woodland birds, the Eurasian sparrowhawk can be found in any habitat and often hunts garden birds in towns and cities. Males tend to take smaller birds, including tits, finches, and sparrows; females catch primarily thrushes and starlings, but are capable of killing birds weighing or more.

The Eurasian sparrowhawk is found throughout the temperate and subtropical parts of the Old World; while birds from the northern parts of the range migrate south for winter, their southern counterparts remain resident or make dispersive movements. Eurasian sparrowhawks breed in suitable woodland of any type, with the nest, measuring up to across, built using twigs in a tree. Four or five pale blue, brown-spotted eggs are laid; the success of the breeding attempt is dependent on the female maintaining a high weight while the male brings her food. The chicks hatch after 33 days and fledge after 24 to 28 days.

The probability of a juvenile surviving its first year is 34%, with 69% of adults surviving from one year to the next. Mortality in young males is greater than that of young females and the typical lifespan is four years. This species is now one of the most common birds of prey in Europe, although the population crashed after the Second World War. Organochlorine insecticides used to treat seeds before sowing built up in the bird population, and the concentrations in Eurasian sparrowhawks were enough to kill some outright and incapacitate others; affected birds laid eggs with fragile shells which broke during incubation. However, its population recovered after the chemicals were banned, and it is now relatively common, classified as being of least concern by BirdLife International.

The Eurasian sparrowhawk's hunting behaviour has brought it into conflict with humans for hundreds of years, particularly racing pigeon owners and people rearing poultry and gamebirds. It has also been blamed for decreases in passerine populations. The increase in population of the Eurasian sparrowhawk coincides with the decline in house sparrows in Britain. Studies of racing pigeon deaths found that Eurasian sparrowhawks were responsible for less than 1%. Falconers have utilised the Eurasian sparrowhawk since at least the 16th century; although the species has a reputation for being difficult to train, it is also praised for its courage. The species features in Teutonic mythology and is mentioned in works by writers including William Shakespeare, Alfred, Lord Tennyson and Ted Hughes.

Taxonomy

Within the family Accipitridae, the Eurasian sparrowhawk is a member of the large genus ''Accipiter'', which consists of small to medium-sized woodland hawks. Most of the Old World members of the genus are called sparrowhawks or goshawks. The species' name dates back to the Middle English word ''sperhauk'' and Old English ''spearhafoc'', a hawk which hunts sparrows. The Old Norse name for the Eurasian sparrowhawk, ''sparrhaukr'', was thought to have been coined by Vikings who encountered falconry in England. English folk names for the Eurasian sparrowhawk include ''blue hawk'', referring to the adult male's colouration, as well as ''hedge hawk'', ''spar hawk'', ''spur hawk'' and ''stone falcon''.

The Eurasian sparrowhawk was described by Carl Linnaeus in his 1758 landmark 10th edition of ''Systema Naturae'', as ''Falco nisus'', but moved to its present genus by French zoologist Mathurin Jacques Brisson in 1760. The current scientific name is derived from the Latin ''accipiter'', meaning 'hawk' and ''nisus'', the sparrowhawk. According to Greek mythology, Nisus, the king of Megara, was turned into a sparrowhawk after his daughter, Scylla, cut off his purple lock of hair to present to her lover (and Nisus' enemy), Minos.

The Eurasian sparrowhawk forms a superspecies with the rufous-chested sparrowhawk of eastern and southern Africa, and possibly the Madagascar sparrowhawk. Geographic variation is clinal, with birds becoming larger and paler in the eastern part of the range compared to the western part. Within the species itself, six subspecies are generally recognised:
* ''A. n. nisus'', the nominate subspecies, was described by Linnaeus in 1758. It breeds from Europe and West Asia to western Siberia and Iran; northern populations winter south to the Mediterranean, Northeast Africa, Arabia and Pakistan.
* ''A. n. nisosimilis'' was described by Samuel Tickell in 1833. It breeds from central and eastern Siberia east to Kamchatka and Japan, and south to northern China. This subspecies is wholly migratory, wintering from Pakistan and India eastwards through Southeast Asia and southern China to Korea and Japan; some even reach Africa. It is very similar to, but slightly larger than, the nominate subspecies.
* ''A. n. melaschistos'' was described by Allan Octavian Hume in 1869. It breeds in mountains from Afghanistan through the Himalayas and southern Tibet to western China, and winters in the plains of South Asia. Larger and longer-tailed than ''nisosimilis'', it has dark slate-coloured upperparts, and more distinct rufous barring on the underparts.
* ''A. n. wolterstorffi'', described by Otto Kleinschmidt in 1900, is resident in Sardinia and Corsica. It is the smallest of all the subspecies, darker on the upperparts and more barred below than the nominate subspecies.
* ''A. n. granti'', described by Richard Bowdler Sharpe in 1890, is confined to Madeira and the Canary Islands. It is small and dark.
* ''A. n. punicus'', described by Erlanger in 1897, is resident in Northwest Africa north of the Sahara. It is very similar to ''nisus'', being large and pale.

Description

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. Marked size difference in this direction 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 long, with a wingspan of and a mass of . He has slate-grey upperparts (sometimes tending to bluish), 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 long, with a wingspan of , and a mass of . 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 (midline) stripe.

The Eurasian sparrowhawk's pale underparts and darker upperparts are an example of countershading, which helps to break up the bird's outline. Countershading is exhibited by birds of prey which hunt birds and other fast-moving animals. The horizontal barring seen on adult Eurasian sparrowhawks is typical of woodland-dwelling predatory birds, while the adult male's bluish colour is also seen in other bird-eating raptors, including the peregrine falcon, the merlin and other ''Accipiters''.

A study, using stuffed bird models, found that small birds are less likely to approach common cuckoos (a brood parasite) which have barred underparts like the Eurasian sparrowhawk. Eurasian reed warblers were found to be more aggressive to cuckoos which looked less hawk-like, meaning that the resemblance to the hawk ( mimicry) helps the cuckoo to access the nests of potential hosts.

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. The outer toe is "fairly long and slender"; the inner toe and back toe are relatively short and thick. The middle toe is very long and can be used to grasp objects, while a protuberance on the underside of the toe means that the digit can be closed without leaving a gap, which helps with gripping.

The flight is a characteristic "flap-flap-glide", with the glide creating an undulating pattern. This species is similar in size to the Levant sparrowhawk, but larger than the shikra (the calls are however different); the male is only slightly larger than the merlin. Because of the overlap in sizes, the female can be confused with the similarly-sized male northern goshawk, but lacks the bulk of that species. Eurasian sparrowhawks are smaller, more slender and have shorter wings, a square-ended tail and fly with faster wingbeats. A confusion species in China is the besra, although ''A. n. melaschistos'' is considerably larger.

In Great Britain, Eurasian sparrowhawks living further north are bigger than their more southerly counterparts, with wing length (the most reliable indicator of body size) increasing by an average of in males, and in females, for each degree further north.

Lifespan and demography

The oldest known wild Eurasian sparrowhawk lived more than two decades; it was found dead in Denmark 20 years and 3 months after having been ringed. The typical lifespan is four years. Data analysis by the British Trust for Ornithology shows that the proportion of juveniles surviving their first year of life is 34%; adult survival from one year to the next is 69%. Birds in their first year of life weigh less than adults, and are especially light in the first two months after reaching independence. There is probably high mortality, especially for young males, during this time. A study in southern Scotland suggested that the greater mortality in young male birds may be due to their smaller size and the smaller size of their prey, which means that they can "last less long between meals". Their size also means that their range of prey is restricted. It has been estimated that a female Eurasian sparrowhawk of average weight could survive for seven days without feeding – three days longer than a male of average weight.

A study of female Eurasian sparrowhawks found "strong evidence" that their rate of survival increased for the first three years of life, and declined for the last five to six years. Senescence (ageing) was the cause of the decline as the birds became older.

Distribution and habitat

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 and had an estimated population of 1.5 million birds in 2009. Although global population trends have not been analysed, numbers seem to be stable, so it has been classified as being of least concern by IUCN. The race ''granti'', with 100 pairs resident on Madeira and 200 pairs on the Canary Islands, is threatened by loss of habitat, egg-collecting and illegal hunting, and is listed on Annex I of the European Commission Birds Directive. It is one of the most common birds of prey in Europe, along with the common kestrel and common buzzard. The Norwegian and Albanian populations are declining and, in many parts of Europe, Eurasian sparrowhawks are still shot. However, this low-level persecution has not affected the populations badly. In the UK, the population increased by 108% between 1970–2005, but saw a 1% decline over 1994–2006. In Ireland it is the most common bird of prey, breeding even near the city centre of Dublin, where it frequents parks and large gardens.

This species is prevalent in most woodland types in its range, and also in more open country with scattered trees. Eurasian sparrowhawks prefer to hunt the edges of wooded areas, 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 ''Accipiter nisus'', 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 if they have a certain density of tall trees.

Eurasian sparrowhawks from colder regions of northern Europe and Asia migrate south for the winter, some to north Africa (some as far as equatorial east 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 (when the ring is read and the bird's whereabouts reported subsequently) was for males and for females.

A study of Eurasian sparrowhawks in southern Scotland found that ringed birds which had been raised on "high grade" territories were recovered in greater proportion than birds which came from "low grade" territories. This suggested that the high grade territories produced young which survived better. The recovery rate also declined with increased elevation of the ground. After the post-fledging period, female birds dispersed greater distances than did males.

Diet and predation

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

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