The Atles dels ocells nidificants de Catalunya i Andorra (Muntaner et al. 1984) was published in 1984 and was, after the Atlas ornitológico de La Rioja (de Juana 1980), only the second-ever bird atlas produced in Spain. For the first time this atlas gave precise indications on a basis of a 10x10 km grid using the Universal Transversal Mercator projection (UTM) of the distribution of 214 breeding birds in Catalonia. The data was collected during the 1975-1983 period, although the greatest effort was made in 1981-1982. A total of 129 people worked on the project, coordinated by Jordi Muntaner, Xavier Ferrer and Albert Martínez-Vilalta from the Vertebrate Department of the Faculty of Biologia at Barcelona University.

Since species distribution varies with time, the Catalan Institute of Ornithology (Institut Català d'Ornitologia, ICO) realised that there was a need to update this first Catalan atlas in order to analyse the trends that had taken place in Catalonia over the intervening 20 years and to update the overall knowledge about the avifauna of the country. Taking into account the current number of Catalan ornithologists and their high skill-levels, and following new tendencies in atlases (Gibbons et al. 1993, Price et al. 1995, Schmid et al. 1998), the new atlas was planned to include additional information about the spatial differences in species abundance. The possibility of possessing objective data on species' trends and their main breeding areas would help both improve knowledge of birds' status in Catalonia and define priorities in relation to the development of biodiversity preservation strategies. Bearing this in mind, the idea was proposed to the Fundació Territori i Paisatge de Caixa de Catalunya and to the Catalan government's Ministry of the Environment. Needless to say, both institutions welcomed the proposition and from the very beginning were crucial to the success of the project.

The present Catalan Breeding Bird Atlas includes information about the distribution of breeding birds in Catalonia during the period 1999-2002, presented in a UTM 10x10 km grid readily comparable with the previous atlas. In this way, an evaluation can be made of all species, including those that have become extinct or started breeding in the period since the previous atlas. Furthermore, maps of relative abundance have been drawn up from information gathered through censusing UTM 1x1 km squares and the use of eco-geographical information layers, and these analyses have provided us with preliminary information about the environmental variables that determine species' distribution and abundance.

This atlas has also played an important role in training nearly 500 participant ornithologists, since the self-imposed responsibility to correctly cover assigned 10x10 km squares made careful identification essential. As well, the standardised methodology used for this atlas forced observers to cover all the different environments within their squares and to perform a minimum number of annual visits. The adoption of these standardised criteria has resulted in very high-quality information. Indeed, this atlas may stand as a paradigmatic example of how the coordination of volunteers can generate material of high scientific value. Lastly, the essentially collective character of this work has played an important role in its divulgation, thereby improving the chances that the atlas will become a useful tool for the preservation of species and their habitats, which is, after all, the raison d'être behind the whole project.