Habitat specialization of birds in the Czech Republic: comparison of objective measures with expert opinion

Capsule Expert-based classification of bird species as habitat specialists and as generalists agrees with objective measures of species' habitat requirements based on large-scale monitoring data. Aims To compare habitat specialization of 137 common bird species breeding in the Czech Republic using three different measures and to test their relationships to species' abundance and habitat associations. Methods Data on bird abundance and surveyed habitats were collected through a standardized monitoring scheme of common breeding species in the Czech Republic. From these data we calculated a quantitative species specialization index (SSI). Canonical correspondence analysis (CCA) was applied to calculate species' habitat niche breadth and the level of association of each species to the main habitats. A panel of 11 local bird experts classified each species as habitat generalist or habitat specialist. Results Species classified as habitat specialists by expert opinion showed higher habitat specialization according to the SSI, as well as according to CCA-based habitat niche breadth. These species were also more closely associated with one of the main habitat types. These relationships were significant even after controlling for abundance. Conclusions As expert opinion accords with the level of species' habitat specialization expressed using two quantitative objective measures, we suggest that these characteristics reflect real interspecific variation in the breadth of habitat requirements in birds. Interspecific differences in habitat specialization are not caused solely by the variability in abundance among species.