The Plaintive Cuckoo, Cacomantis merulinus, is a diminutive bird, stretching a modest 21–24 cm from beak to tail. The adult male dons a grey-brown cloak above and a striking orange underbelly, with a grey head, throat, and upper breast. Its tail feathers are tipped with white, and it stands on yellow legs and feet. The eye is a vivid red, while the bill presents a black upper and yellow lower mandible. The adult female may mirror the male in plumage but is frequently seen in a "hepatic" morph, which is a reddish-brown with dark bars above and paler, faintly barred underparts. A pale stripe adorns the eye, and the tail is banded along its entire length. Juveniles resemble hepatic females but are lighter and exhibit dark streaks rather than bars on the crown and throat.
To identify the Plaintive Cuckoo, look for the male's grey-brown and orange coloration, red eye, and the distinctive white tips on the tail feathers. Females may be trickier to distinguish due to their hepatic morph, but the pale eye stripe and barred tail can be key indicators. Juveniles will appear paler with streaks on the head and throat.
This species is quite adaptable, making its home in a variety of environments including forest edges, open woodlands, scrublands, grasslands, farmlands, parks, and gardens.
The Plaintive Cuckoo is native to Asia, with a range that includes India, Nepal, and China, extending to Indonesia. It is a common sight on many of the larger islands in the Philippines.
A solitary creature by nature, the Plaintive Cuckoo can often be elusive and difficult to spot. It is known for its brood parasitism, laying eggs in the nests of cisticolas, prinias, and tailorbirds, with eggs mimicking those of the host species in appearance but larger in size. Small birds often mob the cuckoo, a defensive behavior to drive the intruder away from their nests.
The male Plaintive Cuckoo is known for its series of plaintive whistles, which include an ascending trio of notes and a sequence of 11 or 12 descending notes.
As a brood parasite, the Plaintive Cuckoo does not build its own nest but instead relies on the nests of other small birds. Its eggs are cunningly similar to those of the host species, though they are notably larger.
The Grey-bellied Cuckoo (Cacomantis passerinus) was once considered a subspecies of the Plaintive Cuckoo but is now often recognized as a separate species.
The diet of the Plaintive Cuckoo consists of various invertebrates, which it forages for across its diverse habitats.
The IUCN Red List has classified the Plaintive Cuckoo as Least Concern, indicating that, currently, there are no immediate threats to its population numbers.