Determine the species presence and distribution in Catalonia during the winter period. Unlike the breeding season, for which there already are two atlases describing the distribution of the breeding birds, there only is scattered and partial information for the winter season, and it does not exist any map for the species present in Catalonia during this period.

Represent the species relative abundance at a UTM 10x10 square scale. The ideal goal is depicting maps from the qualitative abundance estimates provided by the collaborators, instead of the nesting evidence categories typical of breeding atlases.

Depict high-resolution density maps at a UTM 1x1 square scale or similar. Unlike the Catalan Breeding Bird Atlas 1999-2002, it is intended to obtain absolute density maps (i.e. ind/km2) not just relative abundance index maps. In principle, the statistical approach used for obtaining these high-resolution density maps will remain the same: modeling the species abundance according to an array of environmental variables.

Determine the distribution and relative abundance of the sea species off coastal Catalonia. Whereas the ground surveys suffice to determine the presence of reproductive species during the breeding season, in the winter period many sea species never leave the ocean. Therefore, it is needed to design a special methodology for them.

Show the species temporal variability throughout the study period. It should be noted the high variability existing among winters, and frequently within them, in the distribution of many species when compared to a breeding bird atlas. A winter atlas has to be capable of detecting these fluctuations; therefore, it seems more appropriate seizing the changes within the study period rather than just producing a static picture of what happens in a full three year period. This has important implications for the survey design, as will be indicated further on.

Estimate the winter population size. From high-resolution density maps for common birds and from specific censuses for many others. As the Breeding Bird Atlas, qualitative estimates will be the last resort when the other two estimate systems don't provide reliable data.

Obtain population trends for each species that winter in Catalonia. The lack of a previous winter atlas impedes a straightforward estimate of trends. Nevertheless, there are SOCC data available for certain species, and specific surveys conducted for many years for others (e.g. waterbirds). It will be necessary to employ subjective estimates in some instances; in others it won't be possible to obtain reliable trends.

Generate ecological descriptors for each species both by geopositioning censuses and by using GIS layers of environmental variables (selected environments, altitudinal ranges…) in a similar way it was done for the Breeding Bird Atlas.

" Determine the conservation status for the winter populations. This section will totally depend on the maps to be obtained, and on the population sizes and trends. Since the study area may be important for many wintering species (sometimes holding statuses quite unlike their breeding ones) and the paucity of related work conducted in the Mediterranean Basin, the conclusions drawn in this section may be of great interest from an international view point.