The aims of the program are to clarify the basic traits of the breeding biology of our bird population and to evaluate the breeding results in the framework of ornithological monitoring. In Estonia the nesting cards were taken into use in 1959. In 1987, a new format of the nesting card was introduced that covers more aspects of nesting and enables automatic data processing. The data concerning the contents of the nest, as well as the features of the observation region, the nesting site, the biotope, their respective areas and information about the surrounding landscape etc. are marked on the card.

Most valuable are the observatons about such nests that have been visited at least twice, during the egg-laying period as well as during the time when there are nestlings (except the nests of the rare species that are under strict protection). There is the need for filling large quantities of nesting cards in order to be able to evaluate the breeding success of at least the most numerous species each year. By the end of 2001, there were over 40 000 nesting cards in the archive of EOS; all of the massive bulk of information has been digitalised.