Hierococcyx
Hierococcyx or hawk-cuckoos is a genus of birds in the family Cuculidae. They are distributed in South, Southeast, and East Asia. The resemblance to hawks gives this group the generic name of hawk-cuckoos.
They are known to vocalize at their breeding grounds, making identification based on calls easy.
It is sometimes included in the genus Cuculus.
The similarity of these birds to hawks gave rise to an ancient belief that cuckoos transformed themselves into hawks during the winter months, when cuckoos disappeared from Europe.
Mimicry
Hawk-cuckoos closely resemble accipiters in terms of appearance, an elongated body with long wings and tail, greyish or brownish upperparts with paler barred upperparts, as well as their swift direct flight.Underpart barring, a form of Batesian mimicry, tends to alarm small birds targeted by hawk-cuckoos for brood parasitism beyond only shape and colour. The seemingly dangerous appearance of the cuckoo reduces host aggression or mobbing, resulting in more opportunities for the cuckoo to parasitise the host.