Eurasian sparrowhawk
A study, using stuffed bird models, found that small birds are less likely to approach common cuckoos (a brood parasite) which have barred underparts like the Eurasian sparrowhawk. Eurasian reed warblers were found to be more aggressive to cuckoos which looked less hawk-like, meaning that the resemblance to the hawk (mimicry) helps the cuckoo to access the nests of potential hosts.