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BBS Research Introduction Introduced in 1994 to replace the Common Birds Census (CBC), the BBS is now the principle national monitoring scheme for common and widespread bird species in the UK. For the two schemes to be compared and calibrated a period of overlap (1994-2000) was allowed. Analyses comparing trends between these two schemes and the development of combined CBC/BBS indices are discussed in the Population trends section. With any survey of this type, coverage will be patchy and incomplete, so it is therefore important for us to understand how the BBS reflects the true distribution and abundance of the species monitored. Research examining the relationship between bird distribution and abundance and the importance of BBS habitat data for improving our predictions is summarised in under the Spatial variation in abundance heading. The primary role of the BBS is to monitor population trends for a broad range of species, but by recording the distance at which birds are sighted from the transect line, we are able to model the detectability of species within different habitat types using BBS habitat data. We can then derive habitat-specific population indices and national density and population size estimates. A summary of recent work using this methodology is presented in the Population size and density estimates section. The fieldwork methodology for the BBS was finalised after two years of fieldwork trials within the Pilot Census Project in 1992-93. This, and the statistical methods to produce the BBS population trends are discussed in the Methodology and survey design section. As the BBS data set grows with the collection of more and more years’ worth of data, the results from the scheme are being increasingly used to set conservation priorities by Governments and non-Governmental organisations. The use of, and incorporation of BBS results in conservation are discussed in the Conservation section.
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