The riparian Passerines of lake Trasimeno (Umbria, Central Italy): a 11-years study by constant-effort mist-netting

Abstract

From August 1996 to December 2007 at a reedbed site of lake Trasimeno we carried out 562 mist-netting sessions (at least once every ten days). Through the years we kept constantly the same numbers and positions of mist-nets. Mist-netting always started at dawn and stopped at midday, without using any recorded calling. We trapped 13512 birds belonging to 52 species. The collected data allowed us to investigate: the composition and the ecological parameters of the passerine community and their seasonal variations; trends of the most abundant species, calculated taking into account either the whole annual sample or only the breeding population (adult age-class during the breeding season). We found 12 species being dominant at least in one month: Prunella modularis, Cettia cetti, Acrocephalus melanopogon, A. schoenobaenus, A. scirpaceus, A. arundinaceus, Phylloscopus collybita, Sylvia atricapilla, Erithacus rubecula, Cyanistes caeruleus, Remiz pendulinus, Emberiza schoeniclus. The community parameters showed strong seasonal variations: abundance, biomass values and percentage of marshland species were highest from late spring to early autumn, while in the same period diversity and equitability reached their minimum. Considering for each species the complete annual sample, only three species out of 18 showed significant trends: Panurus biarmicus (decrease), Erithacus rubecula (increase), Emberiza schoeniclus (increase). Taking into account the breeding species, we found out significant negative trends for Panurus biarmicus, Cettia cetti, Remiz pendulinus; the remaining species (Acrocephalus scirpaceus, A. arundinaceus, Sylvia atricapilla, Parus major, Passer italiae) showed negative but not significant variations. The decrease of some marshland species might depend (at least in part) on the reedbed loss and degradation.