Alarm and distress calls are used for long-range communications. They can not be transmitted without many alterations. In such circumstances, we should expect birds to make preferential use, for the signal recognition, of those features that are relatively resistant to degradation. To test this hypothesis we have carried out two kinds of experiment with distress calls of different species: one on the signal degradation, the other one on the signal recognition. 1) Signal degradation: We compared re-recordings of a natural distress call at different distances. Our measures showed a high level of degradation for fast FM and AM, and a low level of degradation for harmonic structure and slow FM. 2) Signal recognition: We compared the responses to natural signals and to experimental signals for the different species. Our results showed fast FM and AM were the less important parameters for recognition, and harmonic structure and slow FM were the most important parameters for recognition. Conclusion: The complex structure of a distress call is considerably modified during propagation. Nevertheless, for recognition, the birds use parameters unaltered over distance. The decoding of distress calls is adapted to the constraints of long-range transmission. A behavioural process can compensate for an inappropriate structure of the signal.