Host-Specific Vocal Similarity in Fledgling Levaillant's Cuckoos and Babblers in West Africa

Vocal mimicry in brood parasites may enhance fledgling survival by facilitating care or social acceptance by hosts. We quantified vocal similarity between fledgling Levaillant's cuckoos (Clamator levaillantii) and host fledglings using recordings from two host associations in West Africa and a small comparative set from South Africa. We distinguished two context-defined classes of begging calls: food-transfer calls produced during feeding events and non-transfer calls produced outside food transfer. Multivariate acoustic measurements combined with discriminant and classification analyses showed that non-transfer calls of cuckoos associated with the primary West African host, the Brown Babbler (Turdoides plebejus), closely matched non-transfer calls of host fledglings. In contrast, food-transfer calls were broadly similar across host species and showed little evidence of host-specific vocal similarity in any association. Cuckoos associated with a secondary West African host, the Blackcap Babbler (T. reinwardtii), showed weak or no host-specific vocal similarity overall, although one individual produced a distinctive non-transfer call type that resembled host non-transfer calls. South African material was sparse and revealed no clear host-specific vocal similarity. Because the hosts compared are closely related babblers occupying similar habitats, the restriction of vocal similarity to a single association is unlikely to reflect general ecological convergence or shared constraints on vocal production. Instead, our findings are most consistent with host-mediated selection acting after fledging, potentially favouring calls that promote tolerance or social acceptance within cooperatively breeding host groups. We also report new observations of host aggression towards fledgling cuckoos, highlighting the potential importance of vocal cues during the post-fledging period.