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Sparrowhawks

The sparrowhawk is a small raptors, with short rounded upperparts. Their broad, rounded wings and long tail are adapted for flying between trunks and branches enabling them to weave in and out of trees at high speed. They never hover like kestrels.

Breeding

Sparrowhawks require small clump of trees preferably woodland, for nesting. Nesting territories are spaced regularly, since pairs do not tolerate another nest close by. The distance between nests varies from 0.5 km to 2.1 km. This is related to local food supply, both within the wood and in nearby habitats the better the food supply, the smaller each territory will be.

The nest is usually in lower parts of the canopy close to the trunk of a tree, usually concealed from view. The nest is a sturdy platform of twigs, lined with bark flakes. A central cup will prevent the eggs from rolling out. Nest building can take some weeks and is often completed long before eggs are laid.

Three to six eggs are laid at two-day intervals in May. Incubation lasts 32-35 days. Hatching takes place over two or more days, and the female helps the chicks break out of their shell. The hatchlings are covered in pure white, short down, and their eyes are already partly open. Since hatching takes several days, each chick will be a different size. This is an adaptation to cope with an unpredictable food supply, so that if food is short, the youngest chick will die and reduce the brood to a manageable size. The chicks are brooded almost constantly for their first week, and then progressively less until they are able to control their own body temperature.

The female has sole care of the eggs and young, while the males role from the egg-laying through to fledging is to provide all food required by the female and the chicks. The female will hunt as the chicks get older, but only if the male is unable to catch adequate food by himself.

The chicks are ready to fledge when they are around four weeks old. Males fledge a few days before females. Initially the young leave the nest for brief periods, but continue to return to it to be fed and for the night. Gradually they venture farther and for longer periods, and once their feathers are they begin to chase other birds. Three or four weeks after fledging, the young will have learned to hunt, and will then disperse and begin independent life.

Feeding

Sparrowhawks feed almost entirely on small birds. While the female takes prey up to pigeon size, the smaller male rarely catches anything bigger than the mistle thrush.

Sparrowhawks dont specialise in particular species, but take whatever is available and easy to catch. As a result, the most frequently caught birds are numerous, and conspicuous or easily caught. Species that venture out into open are caught more often than those that stay in cover. Prey varies with habitat, year and season, depending on availability. Hawks time their nesting so that they have chicks when there are plenty of fledglings of small birds around in the same way that blue tits synchronise their breeding to the peak availability of caterpillars. In summer, about 40% of a sparrowhawks diet is fledglings, each species peaking as their young fledge. Hawks spend more time hunting in habitats where prey availability, and hence chance of success, is greatest. Should there be more prey in villages than woods, they would hunt in the villages, and vice versa.

Sparrowhawks employ many hunting techniques, depending on the habitat and prey. They are not built for stamina and long chases, so they have to be able to approach their prey closely, undetected, to have any chance of success. Once spotted, the hawk will have only about three seconds to grab the prey before it escapes. Because the hawk is quite easily seen, and small birds warn others to fly for cover with calls, only about one attack in ten results in capture.

Sparrowhawks go for easy prey in preference the sick, old, weak or injured. They remove primarily birds that would have died of other causes anyway, and make the remaining songbird population fitter and healthier.

Population

Sparrowhawk populations showed significantly decreases up until the 1960s (when they were given full legal protection) due to deforestation reducing the amount of suitable habitat and indiscriminate persecution.

The reduced persecution during World War II allowed sparrowhawk numbers to recover. The numbers were declining again by 1950 as a result of the widespread use of organochlorine pesticides. Sparrowhawk numbers crashed across the UK in the late 1950s, and they practically disappeared from eastern England where the use of these chemicals was the heaviest. Only after the chemical use became restricted, did the birds start to increase in number. During the 1990s, numbers have again declined in some regions, perhaps in response to reduced food availability.

The sparrowhawk is not currently a species of conservation concern. Although DDT residues are still found in the birds, pesticide contamination no longer depresses the population. Persecution is also much reduced since sparrowhawks were given legal protection. Habitat and food availability remain the main limiting and controlling factors.

Legal status

The sparrowhawk is fully protected under the Wildlife and Countryside Act 1981, which makes it an offence to kill, injure or take an adult sparrowhawk, or to take, damage or destroy an active nest or its contents.

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