The size and migratory origins of the population of Hen Harriers Circus cyaneus wintering in England
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Capsule The majority of Hen Harriers Circus cyaneus that spend the winter in England are derived from the British breeding population. Aims To investigate the popular hypothesis that Hen Harriers which over-winter in England are derived principally from breeding populations in mainland Europe. Methods Demographic data were used to estimate numbers of Hen Harriers in Britain at the end of the breeding season. This figure was used, together with data from winter (October-March inclusive) recoveries of Hen Harriers ringed in Britain during the breeding season, to estimate the number of birds from the British breeding population wintering in England and in other parts of Europe. Results It was estimated that Hen Harriers wintering in England are derived primarily from British breeding populations. Published winter population figures for British Hen Harriers may be significant underestimates. Conclusion The link between breeding and wintering populations of Hen Harriers in Britain is closer than previously thought. Conservation action should be spread more equally between the environmental factors which limit populations in different seasons. The winter population in Britain, as monitored by the Hen Harrier Winter Roost Survey, may provide a good indication of the status of the breeding population.