Common Birds Census
|Site types that use this protocol||
The Common Birds Census, operated by BTO, was started in 1962 following trials in 1961, with the aim of monitoring bird population numbers, chiefly on farmland where the growing use of agricultural chemicals and the accelerating rate of hedgerow destruction was causing particular concern. Later other habitats, notably woodland, were included in the scheme. CBC uses a mapping method in which a series of visits are made to all parts of a defined plot during the breeding season, and contacts with birds by sight or sound are recorded on large-scale maps. Information from the series of visits is combined to estimate the number of territories found. Maps of the same plot from different years can be used to assess changes in species densities and to relate these to changes in habitats. CBC results also provide indices of population change for those species which are sufficiently numerous to provide large samples when considered across the sites participating in the scheme.
Note: This protocol is no longer compulsory at ECN sites. The Breeding Bird Survey protocol (BB) is now used instead.