The aim of BDM is to record information about the largest possible areas. It is therefore important to record those species that are typical for our normal landscape.

The objective of the BDM programme is to be able to provide evidence for as large areas as possible. It is therefore important to survey the species that are typical of our normal landscape. Thus the BDM programme focuses on surveying common and widespread species. It is in these species, in particular, where significant changes have occurred in recent years: species that were once very common are rarely found today. By recognizing these types of developments, the BDM can issue early warnings and provide evidence for action before these species have to be included on the Red Lists.

Species diversity of breeding birds in Switzerland	1890	1990	Difference
Number of breeding bird species overall	172	196	+ 14%
Number of widespread breeding bird species	69	42	- 39%
Number of (naturally) rare breeding bird species	15	32	+ 113%

The data show that the total number of species of breeding birds and the number of naturally rare species has increased in Switzerland in the last hundred years. At the same time, however, the number of widespread species has decreased by over one third.

Meadow sage This is an example of a species that used to be considered common but is now classified as rare.

By surveying the common and widespread species in the field, the BDM covers the broadest possible spectrum of species, habitats and environmental conditions.
Naturally, the BDM programme also publishes data on rare species, and for this purpose it can generally rely on data from existing institutions and databases.