Fire is becoming a common phenomenon in Amazonian forest, modifying the structure and composition of natural assemblages. In particular, fire is known to affect patterns of bird diversity in tropical forests, but we have little understanding of the consequences of this for the functional diversity of bird assemblages. For example, frequent fires could act as an environmental filter selecting species with similar traits and, thus, producing a functional clustering pattern. Here, we used body mass, and dietary and foraging traits to calculate the functional structure of understorey bird assemblages in Amazonian forests analysed 3 years after they had passed under three disturbance levels within the 1997–1998 El-Niño period: unburned, burned once and burned twice. First, we tested whether observed levels of functional diversity were different among these forests and also from what one would expect by chance. Then, we investigated if habitat structure was able to predict changes in the functional structure of the studied bird assemblages. In general, there was no evidence of fire reducing functional diversity nor selecting species functionally more similar than expected by chance. Therefore, bird functional diversity was not different from random in unburned and burned forests. This provides some evidence in favour of high functional redundancy of bird species in the tropics, but also indicates that neutral theories of biodiversity, where processes such as dispersal and survival are more important than biological traits to community assembly, may apply to the assemblages studied. Also, we showed that bird assemblages from forests disturbed by wildfires have the tendency to be functionally overdispersed whereas assemblages from pristine forests tend to be functionally clustered. Thus, environmental structure, in part driven by forest responses to fire, is more important than simple categorical definitions of burn frequency for explaining trait-based assembly rules of understorey birds in the Amazon forest.