The Avian Population Estimates Panel (APEP) estimates the national population of most species that breed or winter in Great Britain using a wide range of data and has recently published its latest assessment (Musgrove et al, 2013 British Birds 106, 64 – 100). Together with the abundance estimates made during the 2008-11 Atlas surveys, we can apportion the APEP national estimates to Berkshire on the basis of the proportion of the total national abundance observed in the county.
For a number of species for which independent estimates could be made, they are included in the tables for comparison. This could only be done for the less abundant species and those whose detection rate is likely to have been high, ie a substantial proportion of the birds present are likely to have been counted in surveys. For the majority of breeding species for which independent estimates were made, there was reasonable accord with the estimates derived from the APEP data. Notable exceptions are the owls, for which the abundance estimates, based on daytime surveys, are likely to be poor; and the large gulls, a substantial proportion of which are likely to have been non-breeding birds.