In tropical forest, visual communication is limited by obstacles and birds use mainly the acoustic channel to communicate at long range. However, in this dense vegetation environment, sounds may be greatly altered during transmission over distance. To be effective, information transfer must rely upon parameters resistant to degradation, e.g., a slowly-modulated and low-pitched signal. Nevertheless, a common bird of the Brazilian Atlantic forest, the White-browed Warbler Basileuterus leucoblepharus (Oscines, Parulidae), presents a territorial song having the opposite characteristics: a wide frequency band and high-pitched signal. Thus, the aim of our study was to characterize the propagation-induced modifications of this signal, and to identify its species-specific coding parameters. According to propagation experiments performed in the field at different distances, it appears that the signal is particularly sensitive to degradation through the vegetation: the fine acoustic structures (rapid frequency and amplitude modulations) are strongly modified, and the highest pitched notes tend to disappear at a relatively short distance (about 25 m). Playback experiments show that, for species-specific recognition, birds use the only feature that is resistant to degradation, i.e., the overall slow frequency modulation of the song phrase, and ignore those parameters sensitive to propagation distance. Moreover, birds do not need to hear the whole song, a part of it being sufficient to elicit a behavioural response. Thus, in spite of its structure, the song of the White-browed Warbler succeeds in conveying, over a long range (more than 100m) and through the dense vegetation, the information required for species- specific recognition.