BTO Atlas 2007-2011 - Winter Pilot 2005/06

16 June 2006 | Chris Robinson


The primary, in fact only, purpose of the winter pilots was to gather information for use in designing the survey method which will be used during the main survey period of the new Atlas. Nevertheless, in doing this pilot we have gathered quite a lot of data from one 10km square in Berkshire and these are presented below. No serious conclusions can (or should) be drawn about species distribution or numbers; these data are merely presented for interest and as feedback to the many Berkshire volunteers who took part. Many thanks for your help. BTO have already done some preliminary analysis of data from one UK region and this is described in a separate Atlas newsletter which I am sending to all Winter Pilot surveyors separately.

Summary for Random Rovers (this section written by Brian Clews)

Method - all volunteers were given a map of the 10km square, a 1-page proposal sheet and the BTO recording sheet and instructions. No time or visit constraints were placed upon volunteers, but all were asked to report in half way through to advise what tetrads they had visited so far (in order that I could assess if any were being missed). In addition, volunteers were asked to indicate what proportion of each tetrad they had covered in order that an assessment of overall coverage could be made, in comparison to the timed observer method.

Table 1. Tetrad coverage

"+" indicates figures that are higher than average, "-" indicates figures that are lower than average.

TetradNo. of speciesNo. of visitsTime spent in tetrad (hrs)% of total time% of tetrad covered
A711117.45 +7 +80
C334 -3.45 -1 -70
D415 -8.25360
F7815 +17.45 +7 +80
G451311.5550 -
I44105.45 -2 -50 -
J235 -5.5 -2 -80
K631114.5550 -
L501216.25 +660
M5116 +18.5 +7 +90
P4095.45 -2 -90
Q691519 +760
T6918 +18.45 +7 +80
V661321.45 +7.580
X597 -6.75 -2 -80

If available effort had been applied evenly, there should have been 9 visits per tetrad, each of 1 � hours. From this it can be seen that C, D, I, J, P & X (much of which is in Oxon!) were under-recorded, whilst F, M, T & V (most of which is in Berks) received more than their fair share of attention. Spatially, most squares were adequately covered (notably due to supreme work by RCr) apart from G, I (central Whitchurch) and K (central Theale).

Several volunteers remarked how much they had enjoyed the project, especially from the point of view of finding new places to walk.

Buzzard was only missed in 3 tetrads, Pheasant, Green and G S Woodpecker were only missing from 1 tetrad each!

Feral Pigeon, Woodpigeon, Wren, Robin, Dunnock, Blackbird, Blue Tit, Great Tit, Magpie, Crow, & Chaffinch were the only species found in all tetrads.

Summary for Timed Surveys

Method - volunteers were each allocated one tetrad and were required to make two 3-hour visits, one in the Nov/Dec period, the other in the Jan/Feb period. The survey method was more complex than the Roving one - each 3-hour survey was subdivided into nine 20-minute periods and counts of all species seen or heard during each of these were required. Surveyors were also requested to visit all the different habitat types within their tetrad. An additional complication was that if you went outside the tetrad (sometimes necessary for access) you had to stop timing until your return!

As in the Roving survey, Buzzard was only missed in 3 tetrads (as were Kestrel and Jay, among other species). Pheasant, Pied Wagtail, Dunnock, Jackdaw, Starling and House Sparrow were only missing from 1 tetrad each. Woodpigeon, Wren, Robin, Blackbird, Blue Tit, Great Tit, Magpie, Carrion Crow and Chaffinch were the only species found in all tetrads; a very similar list to the Roving one.

Comparison of Timed and Roving Surveys

Table 2. Species counts per tetrad

Figures in bold are the higher of the two methods.

Species Count Roving71523341567845514423635051644069 694066595352
Species Count Timed4557333554484239353855374655426429423956414744

It can be seen from the above table that counts from all but four of the 22 tetrads surveyed were higher (sometimes considerably so) on the Roving survey. Presumably, a large part of this is due to the significantly greater number of hours spent in the field by the Roving surveyors (see Table 1) and proof, it were needed, that the more time you spend in the field, the more birds you are likely to find!

The results table shows a summary of the findings from each survey for each tetrad. The data from the Roving survey (presence/absence of a species within a tetrad) is compared with that from the Timed survey (maximum count of a species in a tetrad). A tick in the Roving column indicates presence of the species; the number in the Timed columns is the maximum number of the species seen in the two survey visits.


Winter Atlas pilot results (61kb Excel 2000) - a spreadsheet showing which species were record in which tetrads.