BTO Second Atlas of Breeding Birds in Britain and Ireland: 1988-1991.

The dataset was used to produce the second BTO/SOC/IWC Breeding Atlas 1988-91 (Gibbons, D.W., Reid, J.B. &amp; Chapman, R.A. (1993) The new atlas of breeding birds in Britain and Ireland: 1988-1991. T. &amp; A.D. Poyser).<br><br>
Volunteer (mostly) observers compiled as complete a list as possible of breeding bird species in each 10-km square and noted whether the species was simply Seen -- in suitable potential breeding habitat; or Breeding -- a series of standard codes were used to categorise these. In addition an estimate of relative abundance in each 10-km square was compiled from standardized timed visits to at least eight tetrads (2-km squares) within the 10-km square.<br><br>
The dataset comprises: a) records of species presence in 10-km squares with an attribute of Seen or Breeding; b) records of species noted in the timed (2 hour) visit to those tetrads visited as part of the relative abundance assessment. Note that only a proportion of tetrads received such visits.