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Most of the pair bonds are usually formed during the third year as the birds mature and breed for the first time. The bond is usually monogamous and thought to be life long. Following the death of one partner, the mate is usually replaced only in the following autumn or late winter. In resident populations the pair remains together throughout the year, while in migrant populations the pair often separates for the winter. Buzzards are strongly territorial, and defend a nesting territory containing several alternative nest sites, usually 1-3, but up to 14 have been recorded. The same territory is occupied in successive years, normally with a different nest used each time. In resident populations the territory is defended throughout the year. Distribution of territories depends largely on availability of suitable nest sites. Territory size appears to be little affected by ecological conditions, since much of the foraging is done outside the territory. The feeding grounds are often shared with other birds, though hunting perches are defended. The nest is usually in a tree, rocky crag or cliff. It is a substantial structure of branches, twigs, heather and other available material. The average size of a newly built nest is 1m in diameter and 60cm deep. Re-used nests can be 1.5m across. The shallow cup in the nest is lined with green material immediately prior to laying, with further material added throughout the nestling period. The nest is built by both sexes. A clutch of 2-4 white eggs with red and brown markings are laid at three day intervals in mid-April. Incubation is 33-35 days per egg by both sexes but predominantly by the female, beginning with the first egg. The chicks hatch at about two-day intervals. For the first two weeks the young are brooded and fed by the female only, while the food is brought by the male. There is considerable aggression between the chicks. By 25 days both parents hunt and provide food for the young. The young fledge at 50-55 days of age, and are tended by both parents for 6-8 weeks after fledging. One brood a year is raised. Replacement clutches are always smaller than first ones, and are laid if eggs are lost. The breeding success is greatly dependent on food supply and interference from humans. Up to a half of nesting failures can be due to human interference, both illegal and incidental.
On the Continent the breeding densities and performance fluctuate widely between years and regions, its success mirroring vole-cycle peaks. The UK population is less reliant on voles, and as such annual fluctuations in the population are minor. The species suffered from the massive application of persistent pesticides in the 1950s and 1960s, especially in central and western Europe. Persecution limited the distribution, depleted numbers, disrupted population turnover and reduced breeding success over a large part of its range. The recovery since the 1970s is thought to be primarily due to the banning of the harmful pesticides. Today the species is stable or increasing over most of its range. Buzzards once bred throughout Britain and Ireland, but persecution since the 18th century resulted in the species being confined into relict populations in the west of England, Wales and Scotland. Reduced persecution since 1915 allowed the species to gradually recolonise east. |