Avon BTO

Wednesday, March 05, 2008

Some early figures

I now have details of the winter counts in 43 tetrads, or just over 10% of the total, and of 180 hours of recording, and can offer some tentative figures about distribution and population change since 1980.
Only 7 species have been found in every tetrad so far, WP WR D. R. B. MG C. Another nine are in 90% plus tetrads BH PW ST BT GT JD SG CH GR.
To compare with the populations in 1980 I have used the rate at which they were observed then an now. There were 3000 hours of observation in the three winters of the Winter Atlas, and I calculated the rates for each species. This winter I have only 180 hours of recording from a limited range of tetrads, so the comparison is very tentative. The major winners, in percentage change from then to now (ie 25 years) are Buzzrad, up 429% Linnet up 364%, Goldfinch up 285, Robin up 280, Herring Gull up 173, Collared dove up 164 Long-tailed Tit up 126 Gt Spotted Wd up 117, Dunnock up 107 and Green Wd up 100.
The losers, using only species whose numbers were large are Lapwing ( down from 22/hr to 0.3, 98% loss) Common gull down from 9/hr to 2/hr 78%, BH Gull down from 62/hr to 21 and Starling fdwon from 73 to 21 Interestingly Sparrow rates are almost identical.


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