Bob, The method used was the 20-minute area-search of 3 ha (Loyn 1986, Corella
10 (2): 58-60). The usual dimensions were 200 m x 150 m or 300 m x 100 m but
this was allowed to be flexible, depending on terrain and preferences of
individual observers (as long as they kept consistent over time). Many
observers found that 2 ha was a more realistic search area in the time, and I
tend to agree. Areas larger than 3 ha were allowed to be used in open habitats.
A similar method is being used in the current Atlas project, but without numbers
and with 2 ha as the usual standard instead of 3 ha.. Some ABC observers
preferred to use longer time periods (30 minutes) though most adhered to 20
minutes. The ABC method and some results are described in a supplement to the
December issue of Wingspan, by Mike Clarke, Peter Griffioen and myself. For
some studies, I find it useful to use smaller sites (1 ha) and shorter time
periods (10 minutes), to cope with fine-grained habitat mosaics. But the
20-minute 2 ha area search (200 m x 100 m) is probably the most popular and
widely used method. The popularity and effectiveness of the method are
described in RAOU Report 55, by Marilyn Hewish and myself, in comparison with
three other methods. For comparative purposes, we conducted searches at three
consecutive sites, and this became adopted as the standard for the ABC. But
there is no need to adopt such an approach. In designing a survey, the most
important need is to have as much replication as possible (i.e. discrete sites).
Hope this helps. Cheers, Richard.
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