Composition, structure and social role of mixed species flocks of the sub- tropical mountain forest, Tucumán, Argentina

Abstract

“Composition, structure and social role of mixed species flocks of the sub- tropical mountain forest, Tucumán, Argentina”. Mixed-species flocks (BM) are associations of different species of birds that form as a strategy to increase the efficiency of foraging and to reduce the risk of predation. The aim of this study was to determine the structure, compo- sition and social organization of BM in the Subtropical Mountain Forest of Yungas, Tucumán, Argentina. Three sampling sites were determined: Sierra de San Javier Park, Campo de los Alisos National Park and Higuerilla Farm. Daily visits were conducted, from June to August 2006, 2007 and 2009, obtaining 90 samples. The richness and abundance of the flocks were identified as well as stratum and substrate used. One hundred and twenty four BM were observed, totalling 45 known species. Four nuclear species were detected, Chlorospingus flavopectus, Syndactyla rufosuperciliata , Phylloscartes ventralis , and Basileuterus culicivorus. On average the flocks were composed of three to five species, with a range of 2 to 13 species/BM. Foliage was the substrate most used with most used strata going from 2 to 4,9 m. Flock formation would be an important tactic for birds in the subtropical mountain forest of Tucumán to find food and avoid predators during the fall-winter seasons, mainly in the Sierra de San Javier Biological Park.