The grey-bellied cuckoo or the Indian plaintive cuckoo (Cacomantis passerinus) is a cuckoo with widespread occurrence throughout Asia.
The grey-bellied cuckoo is one of the smaller cuckoos, at a total length of about 23 cm. Adults are mainly grey with a white lower belly and undertail. There is a white patch on the wings. Some females are dark-barred reddish brown above with an unbarred tail and have strongly dark-barred whitish underparts. The juvenile resembles the female but is of a duller grey.
The grey-bellied cuckoo is a brood parasite and uses warblers as hosts. It lays a single egg. Its diet consists of a variety of insects and caterpillars. This is a noisy species, with a persistent and loud pee-pip-pee-pee call, with its tail depressed.