Common Cuckoo (Cuculus canorus) nestlings adapt their begging behavior to the host signal system

Common Cuckoos (Cuculus canorus) dependent on parental care for post-hatching demonstrate an intriguing ability to modify their begging vocalizations to ensure maximum care and resources from their interspecific foster parents. Here, we compared begging calls of the Common Cuckoo nestlings fed by four host species, the Grey Bushchat (Saxicola ferreus), Siberian Stonechat (Saxicola maurus), Daurian Redstart (Phoenicurus auroreus), and Oriental Magpie-robin (Copsychus saularis). Results showed that begging calls of the stonechat–, redstart–, and robin–cuckoo resemble those of host species' nestlings in various aspects like low frequency, high frequency, frequency bandwidth and peak frequency, while the bushchat–cuckoo chicks' begging calls were only comparable to their host species in terms of how long they lasted and their peak frequency. In addition, cuckoo nestlings raised in different host nests displayed significant variations in their begging calls in low and peak frequency. This study suggests that cuckoo nestlings do not mimic host species nestlings' begging calls throughout the nestling period, but may tune their begging calls according to host species, while begging calls vary with cuckoo and host species nestlings' ages. Future research should study the parents’ reactions to these calls in different host species for a better understanding of the mechanisms underlying such adaptations.