Geographic patterns in the distribution of Palearctic songbirds

A database was created of digitized equal area distribution maps of 3,036 phylogenetic species of Palearctic songbirds. Biogeographic patterns are reported for two data sets: (1) including all passeriform bird species reported as breeding within the boundaries of our study map, (2) passeriform species restricted in their distribution to our study region, thus excluding the partly extra-limital taxa. With respect to the data set excluding partly extra-limital taxa, the average range size is 238 grid cells (grid cell area: 4,062 km(2)). Analysis of the geographic distribution of species richness for the full data set showed several hotspot regions, mostly located in mountainous areas. The index of range-size rarity identified similar hotspot regions as that for species richness, albeit that the range-size rarity de-emphasized the central Siberian hotspot. Range-size rarity hotspots that are not evident on the measure of species richness concern a great number of islands. Much more prominent on the index of range-size rarity are the Atlas Mountains of northern Africa, the Jabal al Akhdar region in NE Libya, and the eastern border of the Mediterranean. Restricting the analysis of geographic variation to the 25% of the species with smallest ranges resulted in a greatly simplified pattern of hotspots.