The structural and physiognomic characteristics of forests and mountain forest are fundamental aspects that influence the richness, abundance and composition in the bird community. The objective of the present work was to analyse how the vegetation structure could influence the species composition of mixed-species flocks (MSF), along the latitudinal gradient of the subtropical montane forest of the Yungas of Argentina. Eight sites were studied along the 700 km of distribution of the Argentine Yungas. Richness and abundance of MSF were determined. In addition, different variables of composition and structure of the vegetation were analysed. Multivariate analysis indicated that vertical strata coverage and litter depth were the main variables associated with changes in the species composition of MSF along the gradient. Variation in MSF composition within the Yungas was associated with the physiognomy of the subtropical montane forest, which could indicate that it is strongly linked to the condition of the local vegetation. Substantial changes in vegetation could drastically change the composition of the resident flocks.This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.