We thank to Richard Gregory, Arco Van Strien, Adriaan Gmelig Meyling, Ian Burfield, Grégoire Loïs, Ruud Foppen, David Noble and Zoltan Waliczky for valuable comments and help with data collation, analysis and for general support.
Special thanks to the data providers & organisations responsible for national data collection and analysis: Norbert Teufelbauer, Christian Vansteenwegen, Anne Weiserbs, Michael Dvorak, Jean-Paul Jacob, Anny Anselin, Karel Šťastný, Vladimír Bejček, Henning Heldbjerg, Andres Kuresoo, Risto Vaisanen, Frederic Jiguet, Martin Flade, Johannes Schwarz, Tibor Szep, Olivia Crowe, Lorenzo Fornasari, Ainars Aunins, Magne Husby, Przemek Chylarecki, Juan Carlos del Moral, Ramón Martí, Ake Lindström, Hans Schmid, David G. Noble, Ruud P. B. Foppen.
Thanks to the many thousands of skilled volunteer counters responsible for data collection.
The project has been supported by the Royal Society for Protection of Birds (RSPB), the BirdLife International Partner in the UK. Since January 2006 the project has been supported by the European Community. Sole responsibility lies with the author and the European Commission is not responsible for any use that may be made of the information contained in this document. Other significant partners of the project are: Statistics Netherlands, Czech Society for Ornithology (CSO), BirdLife International Partner in the Czech Republic, British Trust for Ornithology (BTO), Dutch Organisation for Field Ornithology (SOVON).
Trend information was derived from annually operated national breeding bird surveys spanning different periods from 18 European countries, obtained through the Pan-European Common Bird Monitoring Scheme (PECBMS). A software package named TRIM (which allows for missing counts in the time series and yields unbiased yearly indices and standard errors using Poisson regression) was used to calculate national species´ indices and then to combine these into supranational indices for species, weighted by estimates of national population sizes. Weighting allows for the fact that different countries hold different proportions of each species´ European population. Updated population size estimates were used for weighting, derived from BirdLife International (2004). Although national schemes differ in count methods in the field, these differences do not influence the supranational results because the indices are standardised before being combined. An improved hierarchical imputation procedure was used to calculate supranational indices.
Countries contributing trend information were: Austria, Belgium (Brussels region), Denmark, France, Federal Republic of Germany, Finland, Ireland, Italy, The Netherlands, Spain, Sweden, and United Kingdom (European Union countries); Latvia, Poland, Czech Republic, and Hungary (countries acceded to the EU in 2004); plus Norway and Switzerland.
Forest or farmland species were selected following Tucker & Evans (1997). A third group (other common species) captured those species frequently monitored but not specialists of those habitats. This includes many generalist species, occurring across a range of varied habitats, but also some birds that are specialists of other habitat types.