Wild bird populations are an important indicator of the health of the countryside, and knowing to what extent bird populations are increasing or decreasing is fundamental to the conservation of birds as well as an indicator of other species. Birds are monitored using standard methods developed by the British Trust for Ornithology. On most sites this involves recording breeding birds within a 1km square using the Breeding Bird Survey (BBS) method. Some sites are continuing to carry out surveys using the Common Bird Census (CBC) method as well as (or instead of) the BBS. On moorland sites the upland BBS method is used.
The methodology used for this protocol can be found on the BTO website.