Divergent altitudinal distributions of bird and bat species richness in a Mediterranean mountain range: patterns and prospects

We studied the distribution of bird and bat species richness in Sierra de Guadarrama (Spain). We observed that bird richness had the highest scores at mid-elevations while bat richness increased monotonically with altitude. Both bird and bat richness were positively related to primary productivity but decreased and increased respectively with woodland cover. In addition, birds tracked vegetation complexity and shrub richness while bats did not track these fine-grained habitat traits. These differences could be related to the spatial scale of habitat use by birds and bats. While birds occur in small home ranges, bats can fly many km away from breeding sites in search of food. The tracking by bats of productive areas would thus blur the effect of fine-grained habitat traits. Our results suggest the need for further research on how the changes observed in productivity and tree cover in these mountains could affect distribution of bird and bat richness.