Signals for parent-offspring recognition: a comparative analysis of the begging calls of cliff swallows and barn swallows

Abstract

Abstract. The individual distinctiveness or information capacity of the chick begging call of the cliff swallow, Hirundo pyrrhonota, and the barn swallow, H. rustica, were compared. The present study examines one hypothesis concerning possible adaptations for parent-offspring recognition in cliff swallows: that the chick call has been elaborated to increase the individual distinctiveness of chick calls. This 'signature' adaptation hypothesis was tested by comparing the information capacity of cliff swallow and barn swallow chick call systems. The analysis revealed that the cliff swallow call contains approximately four bits more information than the barn swallow call. An additional analysis indicated that the information capacity of the cliff swallow call was underestimated more than that of the barn swallow call, so that the approximate four-bit difference is probably a conservative estimate of the true difference. A simple model was developed to illustrate what a four-bit (16×) difference should mean in terms of level of parental recognition permitted by call information; the key parameter is the size of the group (e.g. creche) in which recognition must occur. The model indicates that equal recognition for the two species (e.g. 90% correct discrimination) should occur when the cliff swallow group size is 16 times larger than the barn swallow group size.