© Marcel Burkhardt
Keller, V. (2017)
Vogelwelt 137: 43–52
Grid-based atlases have become a standard way of mapping the distribution of species, in particular for breeding birds. The first atlases only presented the distribution of bird species, often combined with a measure of breeding evidence. The so-called second-generation atlases used statistical methods to map the relative abundance of species often based on information recorded for a sample of smaller units within the standard atlas grid. In more and more countries atlas work has been repeated usually one or more decades after the publication of the first atlas. This offers the possibility to compare changes in distribution and abundance between atlas projects. Comparing successive atlases, however, poses a challenge because the objective to improve the methodology can be in conflict with the one to allow comparisons with the previous atlas. Changes in observer effort and/or geographical coverage make comparisons difficult as well.
Changes in distribution between atlas projects can be shown on maps and/or quantified. Out of 21 repeat atlases of breeding birds 14 showed the distribution from the previous atlas in map form, providing separate maps for each atlas period, combining the data in one map, or making change visible in a separate “change map”. Differences in coverage are usually not indicated. Many atlases provide quantitative information on range change by indicating the number of occupied, new or lost squares or more detailed statistics on changes in number of occupied squares per category of breeding evidence. Difference in observation effort is taken into account in a few cases. Comparisons based on standardised surveys provide robust results but are still rare. The same is true for analyses of changes in abundance, since only a few very recent atlases have repeated standardised approaches suitable for appropriate statistical analyses. The combination of atlas projects with population monitoring programmes and the use of web tools to collect data also offer new possibilities to document and analyse changes in distribution and abundance at different temporal and spatial scales.
keywords: atlas, distribution, breeding birds, review