Winter codes

In winter, the main aim was to record every species that was using the tetrad; birds flying over but not using the tetrad were excluded from the atlas. It was felt that there was not much additional information, apart from habitat details, that would be worth collecting, apart from the size of flocks or roosts. We asked for counts to be included, this request initially being driven by the requirement of the CAWOS database for records to have a number, but in fact the counts, even of a single bird in a tetrad, proved to be especially valuable in allowing a winter population estimate for some species. The winter period was intended to avoid periods of migration and breeding and, to make an atlas sensible, to cover the time when most birds were settled in one area. Having the same dates for all species, regardless of their biology, inevitably entails a compromise, and ‘winter’ was defined as 16 November to the end of February. This was the same choice as was made for the BTO Winter Atlas in 1981/ 82 to 1983/ 84, although the new national Bird Atlas 2007-11 is taking winter records from the beginning of November.

We briefly considered attempting a year-round atlas, but decided against it for a variety of reasons, the key one being the questionable value of mapping birds at periods of the year when they are not settled and just moving through the area, making for problems in interpretation and little value from the information. Also, many species are less conspicuous and are difficult to detect, especially during moult periods. Coverage year-round was thought to be more likely to reflect the distribution of recorders than distribution of birds, and observer fatigue may set in, prejudicing the recording of the more important breeding and wintering seasons.