The Berkshire Bird Index (BBI) is a measure of the change in abundance of commoner species in the county, derived from the BTO’s annual Breeding Bird Survey (BBS). The data are collected by the BTO, which publishes the regional and national trends has provided us with the data shown here. The BBS surveys have been running annually since 1994 with the exception of 2001, when foot and mouth disease prevented most surveying in the countryside, so we now have twenty-five years of data.
A report on the first 25 years of data, including graphs of the changing abundance of our commoner species can be seen here.