In natural conditions all acoustical signals are accompanied by noise. This is particularly obvious when birds are singing during the morning chorus, when the environment is filled with foreign songs. Nevertheless, communication is efficient because there are many ways in which the signal can emerge from noise. For the wren, there are three groups of possibilities: 1. From the physical point of view, the masking is not total. Separation is always possible, at least partially, using patterns of frequency modulation, acoustic level, sound localisation, or sound overlapping avoidance. 2. By applying information theory, it is possible to demonstrate that the information contained in each symbol is easily perceived because it is lowered by redundancy. 3. Decoding is adapted to noise: recognition is the result of an additive process among different cues. There are possibilities of interchanges between them. In conclusion, there is little competition between the songs of different species, and in natural conditions communication is very effective.