Comparison with other breeding bird Atlases

Although in principle it should be possible to compare results from different county atlases, in practice some words of caution are needed because the details of the methods have to be taken into account. For instance, a two-level system (breeding/ present) requires, as a minimum, a pair of birds to be seen and it could have been much quicker to survey a tetrad just ticking off pairs without seeking any higher level of proof. With limited resources of time or people this could be a better way of organising an atlas project. However, some other counties have used this two-level breeding/ present system, lumping together the confirmed and probable categories but, confusingly, have described them all as ‘confirmed’. Another snag in comparing the system used here with those used elsewhere is that some other atlases have used the same breeding status codes but have translated them into different levels of breeding category; for instance, attributing ‘confirmed breeding’ to even a single adult thought to be holding/ defending territory, and ‘probable breeding’ to a singing male in suitable habitat. All of these examples show unfeasibly high apparent levels of ‘confirmed’ breeding.