Mapping Breeding Birds in a Karstic Sinkhole with a Comparison between Different Sampling Methods

Abstract

Karstic sinkholes are peculiar structures hosting specific biological communities. Birds are still little studied in this regard. This note reports, for the first time, original data relating to the density of breeding species occurring within a sinkhole in central Italy obtained with a fine-grained and time-expensive sampling technique (mapping method). The results were compared with data sampled with the point counts method carried out in the same phenological period. We recorded 22 breeding species, all typical of meso-thermophilous forests and ecotonal habitats of hilly central Italy. Among them, two species (Turdus merula and Troglodytes troglodytes), typical of shady, undergrowth habitats, were recorded in the deepest part of the sinkhole (−70 m from the top). No significant differences emerged between the relative frequencies of the species obtained with the two methods, except for Luscinia megarhynchos (overestimated with the mapping method) and Aegithalos caudatus (underestimated). At the community level, the comparison of the two methods revealed similar values in univariate diversity metrics, Whittaker plots did not show a significant difference (ANCOVA test), and ordinary least squares regression between the frequencies showed a highly significant correlation. Therefore, in these peculiar habitats, data obtained from the two methods are comparable: since the point counts method needs lower sampling effort, it appeared to be more effective when compared to the mapping method to study these peculiar habitats.