Assessing woodland ecological characters through a new objective bird community index, the WBCI

Defining a bird species as a ‘forest’ one is often troublesome, owing to the lack of overall ecological knowledge and to differences among regions. In spite of this, in a lot of studies the set of ‘forest’ species is empirically chosen. The authors present an objective measure of the relationship existing, at the Italian national scale, between bird species and woods. Using data of the MITO2000 project (>17000 point-counts), 138 species were scored according to the alpha coefficient of the logistic function linking species-presence and wood-cover. A community index (WBCI), obtained simply as the arithmetic mean of the scores of all present species, has proven (trying it with independent samples) to be strictly linked with the actual degree of wood cover, either at small (e.g. point-count) or large (i.e. 20 km grid Atlas) scale. The WBCI was tested also for its response to various sampling-effort levels, showing stability also with very incomplete data-sets (2/3 the actual species richness). Owing to its stability, specificity, ease, and sensitiveness (allowing to detect also fine temporal habitat change trends), WBCI seems an useful and concise indicator of the complex relationships existing between woodland and birds.