The begging behaviour of nestlings is part of a communication system by which nestlings solicit food from their parents. In the case of brood parasitic species, nestlings in the nests of host species could achieve appropriate begging calls through three different mechanisms: (1) mimicking the host species' begging calls, (2) emitting a begging call that stimulates a wide range of hosts or (3) tuning the begging call in a way that optimizes food provisioning by foster parents. All three mechanisms could occur as a result of post-hatching environmental factors, or they may be innate when parasitic females specialize on particular host species. In this study we analysed the begging calls of Great Spotted Cuckoo nestlings in nests of its two main hosts, Eurasian Magpie Pica pica and Carrion Crow Corvus corone corone. We did not find support for the previously suggested mimetic call of cuckoo nestlings, as the structure of begging calls did not differ with respect to host species. In addition, the number of notes per call was the only trait of Cuckoo begging calls that differed when parasitizing different host species, but it was in the opposite direction from that of the begging calls of the nestlings of the two host species. Furthermore, cross-fostering experiments with nestlings that hatched in nests of the two host species yielded calls that did not support the possibility of genetic determination of begging calls of Cuckoos parasitizing different host species (e.g. host species of origin). Moreover, we found a significant effect of the identity of the host species in explaining variation in the number of notes per call. Therefore, our results suggest that Cuckoo nestlings are able to adjust their begging calls after hatching in nests of different host species by learning efficient begging displays.