Landscape heterogeneity affects the use of sampling methods: a case study of bird communities in mountains of Central Italy

Abstract

The point count method (PCM) and time species count (TSC) are thought to be applicable to specific bird assemblages and habitat types and to give different kind of outputs: quantitative (abundances) and qualitative (scores), respectively. In this work, we tested if the faster TSC method can be used instead of the time-consuming PCM. We compared results obtained from the application of both methods to bird assemblages in three different habitat types in mountains of Central Italy with different levels of spatial heterogeneity (oak and beech woods, and open-forest mosaics). The application of both methods to the forest ecosystems revealed the absence of a direct correlation between PCM abundance values and TSC mean scores, highlighting that the latter method did not explain the variation in species abundance. The opposite was true in the mosaic habitats. In the Apennine forest ecosystems, species sampled first in the TSC sampling sessions did not correlate with species abundance values evaluated by means of PCM. The species with the highest PCM values (i.e., the more abundant species) were randomly distributed in all of the TSC 10-min sampling subsessions. Therefore, we rejected the hypothesis that the species sampled first (e.g., in the first 10 min) in TSC are more abundant than those sampled in the next 10 min subsession, and so on. This result differs greatly from that found for non-Mediterranean habitat types that are richer in species number (e.g., tropical forests and savannahs), where scores obtained for single bird species when applying the TSC method correlate well with the species abundance parameters obtained using quantitative methods. In the mountainous complex of the Mediterranean area, the TSC method should only be applied in mosaic habitats, which are richer in species, more spatially heterogeneous, and possess a high γ-diversity at the landscape scale, and thus show a direct correlation between species abundance and TSC scores.