Once regarded as Britain's most abundant owl species, Barn Owl Tyto alba numbers declined substantially from 1850 to 1950. While more recent surveys suggest that numbers may now have stabilized, breeding range declines and the species' unfavourable European conservation status have resulted in its inclusion on the Birds of Conservation Concern Amber List. As existing schemes were not suited to monitoring the abundance of low density, nocturnal species, the Barn Owl Monitoring Programme (BOMP) was established by the British Trust for Ornithology in 2000, assisted by the Wildlife Conservation Partnership. Under BOMP methodology, approximately 600 potential breeding sites (c. 10% of the national population) located throughout the British Isles are visited by volunteer observers each year who record owl occupancy and productivity. These data are used to assess long-term trends, and the results from the first six years of data collection (2000–05) are presented in this paper. As expected, given the short time-span of data collection, there was no strong evidence for a significant temporal trend in either occupancy or productivity. Habitat type appears to play a significant role in determining both occupancy rates and productivity. A greater proportion of sites in areas of natural or semi-natural grassland were occupied by Barn Owls and broods produced at these sites were significantly larger than those produced in pastoral or arable habitats. Areas of rough grassland are likely to support greater numbers of small mammals, particularly voles Microtus spp., providing more food for adults and nestlings. There was some evidence to suggest that occupancy rates were higher towards the western part of the country, possibly due to the milder winter conditions in these areas.
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Vol. 97 • No. 4