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

Quality Control

The maps as published are considered a true representation of the distribution and relative abundance of each species at a national level during the survey period. There will be some gaps in individual squares, especially for some of the more elusive and rarer species and some bias due to observer intensity.

Method steps

1. Specific fieldwork was conducted by mainly volunteer observers although professional help was used in remoter areas. Two kinds of survey work were carried out:1) Timed Tetrad Visits (TTVs): Observers visited a tetrad (2-km square) for two hours (and only two hours), with a stated preference for this period to be split into two one-hour visits one early in the season and one late. During this time a species list was compiled and the individuals of some (specified) species were counted. Tetrads were eligible for coverage if their centre was on land. Coverage of a minimum of eight such tetrads in each 10-km square was requested although the choice of which ones was left to the observer(s) with the proviso that they should aim to represent the major habitats within the 10-km square. Where there were fewer than eight eligible tetrads, all tetrads were surveyed. These lists were then used to calculate the proportion of tetrads visited in which each species was recorded in the two-hour visit, a figure which was then used as an estimate of relative abundance in the 10-km square. For the specified count species, the relative abundance index was based on the mean count across surveyed tetrads. Note that in some remote areas the TTV comprised a single visit of two hours.2) Supplementary Records: In addition to the TTVs records of any other species in the 10-km square were requested. Observers were particularly asked to look for elusive species such as nocturnal ones which were likely to be missed during TTVs.In all cases observers were asked to note whether the species was 'Seen' or 'Breeding' in the 10-km square. 'Seen' was defined as being seen in the breeding season in suitable habitat. 'Breeding' was defined by a series of specific activities, for example apparently holding territory, nest found, recent fledglings seen. A full list of activities considered to be 'Breeding' is in the book (p.4).In some cases records from such as Local Bird Reports, seabird colony counts and other surveys were added to the dataset to provide a more complete species list and/or more accurate abundance information for each 10-km square.For 10-km squares the dataset records the maximum category of breeding evidence obtained in each 10-km square. For tetrads the dataset records the species recorded during the TTV.For a more comprehensive description of the Methods see www.bto.org/birdatlas/previous/old_methods.htm and the Introduction to the published book.

Species Groups recorded: bird.

This datasets contains data only for the island of Ireland, but is part of the larger Britain and Ireland master dataset held by the British Trust for Ornithology at Thetford, U.K. All 10-km squares within the island of Ireland with more than a very small amount of land were visited.