Composition and dynamics of mixed flocks of birds in a remnant of Submontane Atlantic Rain Forest in southern Brazil

Mixed flocks are associations of two or more species that are formed and maintained through mutual behavioral responses, with advantages such as maximizing foraging and protecting against predation. This study aimed to evaluate the composition, temporal dynamics, and presence of core species in mixed flocks of birds in a remnant of the Submontane Atlantic Rain Forest in the Parque Nacional Aparados da Serra, southern Santa Catarina state, Brazil. Data collection took place from October 2016 to September 2017 through monthly campaigns, consisting of three consecutive observation days, with sampling sessions of six hours per day, resulting in a total effort of 216 h of observations. For each contact with the flocks, we recorded the species and number of individuals, stratum of occurrence, substrates of search, and agonistic interactions. We recorded 152 mixed flocks, with a total of 76 species belonging to 24 families, and five orders, with Thraupidae, Tyrannidae, Furnariidae, and Rhynchocyclidae being the richest. The flocks had an average of 4.5 ± 2.7 species and 8.7 ± 5.8 individuals, with richness and the number of individuals being positively correlated (R² = 0.8). Mixed flocks occurred throughout the year. There was a great variation in the number of contacts from October to February (from 5 to 20 contacts). Meanwhile from March to September, the coldest period of the year in the region, the number of contacts did not vary (from 9 to 14 contacts). However, there was no difference in the number of contacts between these months (z = 0.37; p = 0.691). Basileuterus culicivorus and Habia rubica were the core species because, in addition to their high participation (46.7 and 32.9%, respectively), they showed frequent and conspicuous movement and vocalization. Thus, a high capacity to enlist a greater number of individuals from different species for the flocks was demonstrated.