Nestlings of the common cuckoo do not mimic begging calls of two closely related Acrocephalus hosts

Abstract

Nestlings of the obligate brood-parasitic common cuckoo, Cuculus canorus, use diverse signals to manipulate host parents into feeding them. Begging calls, one of the most prominent parent–offspring communication signals, have been suggested to differ between cuckoos parasitizing different host species but the call characteristics involved differ between studies. We studied nestling begging calls of the cuckoo and two closely related cuckoo hosts breeding in sympatry, the great reed warbler, Acrocephalus arundinaceus, and the reed warbler, Acrocephalus scirpaceus, to determine whether cuckoo nestlings adjust their begging calls according to the host species and if these calls vary with cuckoo age and sex. We found that begging calls of host nestlings differed markedly between species but there was no difference in the begging calls of cuckoo nestlings raised by great reed warblers and those raised by reed warblers. These results suggest that cuckoo nestlings do not adjust begging vocalizations to match host species but rather use general begging call features to solicit food. However, their call frequency band narrowed, syllable duration shortened and call rate tended to increase with increasing age. None of the begging call characteristics differed between the sexes. The rapid development of cuckoo begging call parameters during ontogeny suggests that any comparisons of begging calls of cuckoo nestlings raised by different host species must control for nestling age. Finally, some discordant conclusions of this and other studies emphasize how little we understand parasite–host communication.