Search

Capsule There are regional and habitat differences, but no long-term decline in numbers. Aims To review the evidence for declining Swallow populations in Britain, based on the British Trust for Ornithology's long-running Common Birds Census (CBC) and suggest possible causes. Methods Trends were fitted to CBC data for 1964-98 using a generalized linear modelling framework and analysed with regard to specific regions and habitats. Current habitat use, particularly of different farming types, was characterized using data from the Breeding Bird Survey. Correlations between Swallow population size and loss of nest-sites and rainfall in the non-breeding grounds were examined. Results Although Swallow numbers show large annual fluctuations, there is no evidence for a long-term decline on CBC plots. Numbers seem to have declined on farms in eastern England and in non-farmland habitats, but were not correlated with changes in cattle numbers or with an index of regional changes in nest-site availability. The number of Swallows breeding each year in Britain was not correlated with rainfall on their wintering grounds but was correlated with rainfall in the western Sahel on spring migration. Conclusion Changes in farming practice do not appear to have had a long-term effect on Swallow numbers. Although Swallows show high breeding site fidelity, changes in breeding location may mean local declines are not reflected in regional or national population trends. [ABSTRACT FROM AUTHOR]

A national survey of breeding Barn Owls was undertaken between 1995 and 1997 using intensive fieldwork methods within a stratified sample of 1100 2 × 2-km survey squares selected at random from those available. Each year, fieldwork was divided into two sessions: one to locate potential nest-sites (winter session) and one to determine occupancy of these sites (summer session). Fieldworkers spent an average of 30 hours on fieldwork within each survey square. The survey produced national population estimates of 2830 (95% confidence intervals: 1952-3761) breeding pairs for 1995, 3967 (95% CI: 2785-5252) for 1996 and 3951 (95% CI: 2769-5214) for 1997. Analysis taking account of the poor coverage in certain regions of high Barn Owl density in 1995 suggests that a population estimate of 3480 would be more accurate for that year. Regional and temporal variations in estimates were examined and interpreted in relation to Barn Owl productivity and ecology. Validation of fieldwork efficiency was carried out within a random selection of the available survey tetrads, demonstrating that fieldworkers achieved a high degree of survey reliability. This paper provides a baseline population estimate and standardized, repeatable methods, allowing future population changes to be monitored effectively. [ABSTRACT FROM AUTHOR]