Abstract
Several woodland bird species have declined markedly in abundance in England over the past 40 years, whilst the grey squirrel Sciurus carolinensis, a non-native nest predator, has increased. Given the timing, there has been concern that grey squirrels have driven these declines, although there is little data to support this view. Using novel analytical methods and extensive national bird and grey squirrel monitoring data, we examine whether there is evidence that woodland bird populations in England have been depressed by grey squirrels and whether there is a relationship between nest failure and squirrel numbers. Our results indicate that grey squirrels are very unlikely to have driven observed declines of woodland birds in recent years, although the number of associations, positive as well as negative, between grey squirrels and woodland birds is greater than expected by chance. For this reason, we cannot exclude the possibility that the populations of a small number of bird species, principally increasing species, have been depressed to some degree at sites where a greater number of grey squirrels were present. Of these species, perhaps the most convincing evidence is for Common Blackbird Turdus merula and Eurasian Collared Dove Streptopelia decaocto where nest record data also identified a positive relationship between nest failure at the egg stage and squirrel abundance.
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Acknowledgments
We are grateful to the thousands of volunteers who have contributed to the BTO/JNCC/RSPB Breeding Bird Survey and the BTO Nest Record Scheme, which provided the data on which these analyses are based. The BBS is jointly funded by the BTO, JNCC and the Royal Society for the Protection for Birds (RSPB). The Nest Record Scheme is jointly funded by the BTO and JNCC. We would like to thank Steve Freeman for statistical advice and comments and Dan Chamberlain for comments on an earlier draft. This work was funded by Natural England.
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Communicated by P. H. Becker.
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Newson, S.E., Leech, D.I., Hewson, C.M. et al. Potential impact of grey squirrels Sciurus carolinensis on woodland bird populations in England. J Ornithol 151, 211–218 (2010). https://doi.org/10.1007/s10336-009-0445-8
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DOI: https://doi.org/10.1007/s10336-009-0445-8