Avon BTO

Friday, March 21, 2008

Winter summary

I have now had most of the paper surveys in, and a number of people have added in entries on to the website; as far as I can see 237 tetrads have had their full winter survey, which is a magnificent start.
I have the details of both counts for 58 of these tetrads. Though this looks like a large sample, it is biassed in some ways, and hence comparisons with the past must be tantative.
I have just put the results of the first winter tetrad atlas on to my database. The method was not the same- observers were simply asked to identify all the species in the tetrad during a winter, with no time limit, so that elusive birds were much more frequently observed than they would be in the four hour limit of this survey.
However of 103 species 68 were recorded this time within 10% either way of their distribution 25 years ago. Ignoring seven elusive species, 15 species show a decline in distribution and 13 an increase. The most dramatic declines in percentages were L. 51, Y.49, M.49, SD 42, S. 37, K. 34, RO 30, CM 24. The most dramatic increases were BZ 41, GO 34, HG 30, LT 26, RN 26, CD 30 and MA 18.
Some of these results are surprising, RN did not feature in the last winter atlas, and LT had sufferred severely during the 81/82 winter. The results for Y. and MA may well alter when the full results become clear, but I suspect that the others are about right.
One striking results is that Starling has sufferred a 58% fall in numbers, but only 2% in distribution, while Sparrow has fallen by 9% only in numbers, but by 12% in distribution- this reflects its sedentary nature, and I suspect the Sparrow numbers will show a further fall when the full results are in.
I hope everyone is all set for the breeding season surveys, and that everyone will make an effort to obtain Proof of breeding for as many species as possible.


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