WHY DO DISTRESS CALLS EVOKE INTERSPECIFIC RESPONSES - AN EXPERIMENTAL-STUDY APPLIED TO SOME SPECIES OF BIRDS

Distress calls of birds are well-known to elicit interspecific responses when they are broadcast to different species. We suggest that the interspecificity phenomenon results from the use of similar laws of decoding by all species. To support this hypothesis, we broadcast a simplified synthetic call to five species of birds (Larus argentatus, L. ridibundus, Vanellus vanellus, Corvus frugilegus and Sturnus vulgaris). This synthetic call was built by keeping all the parameters involved in the process of recognition and common to the different species and by removing species specific markers. No significant differences were found between this signal and specific control signals (one for each species). These results support the hypothesis that the interspecificity of responses is linked to similarities in the process of identification of the distress message. In addition, the decoding law of such calls appears to conform to selection pressures imposed by physical laws of sound transmission at long range.