I Picidi lungo il corso del fiume Isonzo: analisi quantitativa e scelta del sito di nidificazione

Abstract

This study examined nest-site selection of four woodpecker species living in the floodplain forests of the Isonzo river (Gorizia). 14 plots were examined for a total area of 278 ha. We estimated the number of pairs for the whole study area: 60 of the Great Spotted Woodpecker Dendrocopos major, 30 of the Green Woodpecker Picus viridis, 13 of the Lesser Spotted Woodpecker Dendrocopos minor, 4 of the Black Woodpecker Dryocopus martius. The presence of a pair is not correlated with the plot area. The density of contacts and pairs is greater in forests with prevalence of old poplar Populus sp. We calculated an index to analyse the whole Picidae community and to compare the different plots. This index has shown a good correlation with the percentage of old poplar trees of a plot. Finally, habitat variables in 15 m radius subplots centered on nest trees and on potentially suitable trees were analyzed. The Black Woodpecker prefers high poplar density with a large diameter, preferably dead. On the basis of these results we believe that the riverine forest management has to consider the preservation of small natural plots with prevalence of old poplar trees.