Avon BTO

Friday, March 28, 2008

Ready for the breeding season?

A few days to go before the Breeding season formally starts. A few points worth making.
a) The first count must be bnetween April 1 and may 31st- so I expect many people will go for a may visit. The second count lies between June 1 and July 31, and I expect most people will opt for June. There should be a months gap between the two.
b) Many observers doing Atlas are also doing BBS, and BBS splits its two surveys on May 15th. Dont get confused!
c) Dont muddle any BBS counts with any Atlas counts. The Atlas tetrad survey is a time limited survey to all habitats within the tetrad. The BBS survey is a double transect across a one-km square.
d) Colony Counts. The Atlas breeding season surevy asks on its last page for counts of apparently occupied nests of colonial species. For us this means Heron, LB and HG, and Rook. If you come across any of these stop the clock and count. I have sent details of known Rookeries in tetrads being covered to observers because it is legitimate to count the colony quite separately from the timed count, and as rooks cant be accurately counted once leaves are out it is best to count them early. But you may of course come across a Rookery or Heronry during a timed count.
Finally as far as I can see 242 tetrads were fully covered during the winter season. One or two observers have had to drop out for various reasons, and a number have reserved tetrads for the second atlas season, so of 400 tetrads to cover, 297 have observers. If you want to book yourself a tetrad for the second season, go to the website and see what is available. And also you might consider looking at the needs of Wiltshire or Somerset, or even look across the estuary.

Good luck this summer.

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.

Saturday, March 08, 2008

Counting Rooks nests

One of the objectives of the Atlas is to get a good estimate of the number of nests of colonial species, and for us this primarily means Rooks. I have been looking at the total of Rooks nests in each of the tetrads that we will be covering this summer, and am about to send out a list of sites in their tetrad to each observer. The data comes from 2005, and on average there is a turn-over of about 15 rookeries a year, so it may well be that somes of the sites will have been deserted, and that others will have been created, and certainly the number of nests will have changed.
Rooks can only be counted before leafing, which means that those observers ought to do an early April count. This can be done separately from the normal tetrad count, and sent in as a Roving record, or as part of a tetrad count, stopping the clock while the count is made. Counts can often be done with reasonable accuracy from a distance. Some tetrads have only a single rookery, some have up to eight.
To give an idea of the scale, in 2005 we counted 6000 nests, which was 2000 fewer than in 2000, and this did not include any Mendip rookeries.
Casual records of Rookeries will also be of value, simply as a check, and should be sent in as Roving records. The total nests in a rookery inceases over time, as young birds join on the periphery-older birds take the best positions and have laid by the beginning of April, so that counts made in late March will give a very good idea of totals.

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.

Saturday, March 01, 2008

Winter ends, roll on Summer

I expect you will have seen the neat colours on the Latest Results, Avon, map, showing those tetrads that have only had one visit in the winter, those that are not booked for both winter and summer, and those that have just ahd a second visit. If you have not yer put your records in on line, please do so promptly. If you were unable to do a second visit the tetrad should be redone next winter with two visits.
The Challenge of the breeding season is a month away- and it is not too early either to book additional tetrads either to start next winter and the following summer, or to start this summer and be completed next winter.
The aim of the breeding season survey, apart form tetrad surveys and a species list for each 10km square, is to get the Proved Breeding evidence for every breeding species in every 10k square- and this will not be easy.
Good Luck