Habitat selection and population size of Corn BuntingsMiliaria calandrabreeding in Britain in 1993

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Abstract
This paper presents the results of a survey of breeding Corn Buntings in Britain in 1993. Numbers of Corn Buntings and land–use types and field boundaries present were recorded by volunteers from over 1300 tetrads selected across the range of the species in Britain. The British breeding population was estimated at around 20 000 territories. Bootstrapped 95% confidence limits differed from the calculated estimates by approximately 20%. Population sizes in different regions of Britain were positively correlated with the proportion of total farmland under tillage and cereals and with the total areas of tillage and cereals, but not with the proportion of tillage made up by cereals nor with the overall area of farmland. Densities in occupied 10-km squares were lower in regions which experienced the greatest declines in distribution between 1968–72 and 1988–91. Areas abandoned by breeding birds between 1968–72 and 1988–91 were higher in altitude and held more grassland and less tilled land than areas where birds were retained. Areas which gained breeding birds during the same period contained more tilled land than areas where the species was not recorded as breeding in either Breeding Atlas. Tilled land of all types was more widespread in tetrads which held Corn Buntings than in those where no birds were recorded. Ten-kilometre squares which retained breeding Corn Buntings between the 2 Breeding Atlas periods and those which lost them both showed an increase in their average area of cereals and total tillage between 1969 and 1988, but 10-km squares which retained breeding birds held around twice the area of both land-use types in both years. The results suggest that changes in cereal area are unlikely to be the main cause of recent population declines. The possibility of a 'source-sink' metapopulation basis to the distribution of Corn Buntings in Britain, and the practical conservation implications of this possibility, are discussed.