Resumo

MARTINEZ, Omar. Species composition and substrate use by mixed-species bird flocks in an Andean cloud forest of Bolivia. Ecología en Bolivia [online]. 2003, vol.38, n.2, pp.99-120. ISSN 1605-2528.

Based on capture-recapture, color-banding, point counts, and random walk methods, the species composition of mixed-species feeding flocks and the relative use of various foraging substrates were studied in the cloud forest of the Mina Copacabana, Cotapata (La Paz, Bolivia). A total of 25 complete and 32 incomplete, mixed-species flocks were observed during a period of 6 months (April to September of 1997). A total of 73 species belonging to 9 families were registered, 33 (45%) formed mixed-species flocks and 40 (55%) were solitaries. Thraupids and Tyrannids were the best represented groups in the mixed-species flocks, with 13 and 5 species, respectively. The Scarletbellied Mountain-Tanager (Anisognathus igniventris) was the species most often observed in mixed-species flocks (being present in 16 of the 25 flocks) whilst the Pearled Treerunner (Margarornis squamiger) was present in 10 of the flocks. The Hooded Mountain-Tanager (Buthraupis montana) was the most numerous species (with a total of 45 individuals in 6 flocks) followed by the Spectacled Whitestart (Myioborus melanocephalus) with 33 individuals in 9 flocks. The canopy was the most frequently used foraging stratum (with a total of 22 species, 12 or 66.7% of which were exclusive to that stratum) followed by the midstory (8 species, 24.2%) and the lower strata (3 species, 9.1%). Seven species were classified as part of the active nucleus of the flock, 7 as to the passive nucleus and 19 as attendants. Twenty (60.6%) of the 33 species observed in the mixedspecies flocks were brightly coloured. The substrate use was influenced by the leaf-branch and the epiphyte categories, 26 and 16 species, respectively. Seven species used the bamboo substrate, two of which, the Yellow-billed Cacique (Amblycercus holosericeus) and the Plush-capped Finch (Catamblyrhynchus diadema) were bamboo specialists. A higher number of species forming mixedspecies flocks was found at the Mina Copacabana site (33 species) compared to the Cotapata (21), Chuspipata (27), and Montes Carpish (24) sites. Nine species (e.g. Pseudocolaptes boissonneautii, Pyrrhomyias cinnamomea) were frequent members of mixed-species flocks in both Mina Copacabana and Montes Carpish sites. In general, we encountered more similarities between Mina Copacabana and Chuspipata flocks.

Palavras-chave : Birds; mixed-species flocks; cloud forest; Bolivia; nuclear and attendant species.

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