1 ECOTROPICA Volume 14 2008 No. 1 INTRODUCTION A variety of organisms inhabit treefall gaps or open- ings in intact forest (Schemske & Brokaw 1981, Wun- derle et al. 1987, Levey 1988b, Restrepo et al. 1999, Fuller 2000, Guilherme & Cintra 2001). However, most previous studies have only compared species presence in gaps with nearby forest understory and have not related their occurrence to habitat variables within the gaps. This approach disregards the vast heterogeneity gaps show with respect to the amount of incident light, topographic, and edaphic conditions (Whitmore 1989), factors that play a significant role in determining floristic composition and vegetation structure (Uhl 1982, Denslow 1987, Uhl et al. 1988, Whitmore 1989, Schnitzer & Carson 2001). So far, we know of no study that has addressed how the com- bined effects of such factors may influence the struc- ture and composition of bird communities using tree- fall gaps. In tropical rain forests usually only 1–3% of in- cident light from the sun reaches the forest floor (Chazdon & Fetcher 1984), but most tree species cannot complete their life cycle under these conditions (Schupp et al. 1989). Therefore treefall gaps are critical in driving forest regeneration (Popma et al. 1988, ECOTROPICA 14: 1–13, 2008 © Society for Tropical Ecology THE HETEROGENEITY OF AMAZONIAN TREEFALL GAPS AND BIRD COMMUNITY COMPOSITION Cristina Banks-Leite 1,2 & Renato Cintra 1 1 Departamento de Ecologia, Instituto Nacional de Pesquisas da Amazônia Cx Postal 478, Manaus, Brasil 2 LEPaC, Departamento de Ecologia, Universidade de São Paulo, Rua do Matão 321, travessa 14, CEP 05508-900, São Paulo, Brasil Abstract. It is widely recognized that the physical disturbances created by treefall gaps influence animal communities in tropical forests. However, how the bird community is affected by the internal heterogeneity of gaps is still unstudied. Twenty- five treefall gaps were sampled for their understory and canopy bird assemblages in a mature Central Amazonian rain forest. Mist nets, binoculars, and tape recorders were used to sample the bird community. Environmental variables were chosen for their known influence on forest regeneration through variation in sunlight exposure (gap size, canopy openness, aspect, gap orientation, and elevation), and for representing gap dynamics (gap age and vegetation structure). The bird community attributes analyzed were species abundance, richness, and community composition. Species richness and relative abundance did not vary significantly according to gap characteristics. The gap variables that most influenced bird community composition were related to sunlight exposure, and frugivores and nectarivores were the most affected guilds. Insectivores were affected only by gap size while understory species were not affected at all. The results indicate that differences among treefall gaps in the Manaus region may have a stronger influence just on some species, as shown by changes in community composition only than on overall species abundance and richness. Among all groups, frugivorous and nectarivorous birds were shown to be the most affected guilds by gap environmental variables. As previously suggested, we bring more evidence showing that treefall gaps may indeed function as “keystone places” for birds for their role in sustaining frugivores and nectarivores in periods of fruit scarcity in the forest. Accepted 15 January 2008. Key words : Amazon, birds, community ecology, frugivory, gaps, tropical rain forest. e-mail: banks@ib.usp.br