Does host-absent vocalisation of common cuckoo chicks increase hosts’ food provisioning behaviour?

Abstract

Parent-absent vocalisation is produced by nestlings of several bird families when the parents are away from the nest. An analogous behaviour, host-absent vocalisation, has been found in some species of avian brood parasites and there are several explanations why this behaviour could have evolved. Using playback experiments, we examined whether polygynous great reed warblers (Acrocephalus arundinaceus) adjust their food provisioning behaviour in response to host-absent begging vocalisation uttered by the common cuckoo (Cuculus canorus) chicks. We found that both on monogamous and polygynous nests, host pair members responded to the broadcasted parasite begging signals by increasing their feeding rates; yet, they did not deliver larger volumes of food as a consequence of somewhat smaller prey brought per visit. Nevertheless, we propose that host-absent vocalisation of the common cuckoo chick may still represent a signal of hunger that may compensate for other, deficient components of parasite begging display. However, the efficiency of this signal may be limited by the foster parents’ provisioning abilities and local prey availability. Bird chicks beg loudly for food when their parents are at the nest, as well as when the parents search for food elsewhere. The same applies to young parasites raised by their hosts. Experimental playback of host-absent begging calls of cuckoo chicks increased great reed warbler feeding frequency but had no effect on the volume of food delivered. Host-absent vocalisation may represent signal of hunger; however, its effectiveness may be limited by provisioning abilities of the hosts.