The Common Hawk-cuckoo (Cuculus varius) also commonly called the Brainfever bird, is a species of cuckoo that occurs in Punjab, Pakistan east across much of the Indian peninsula, Bangladesh, and Sri Lanka. It is found at altitudes of 2600 feet in the Himalayas. Most birds are resident but ones that occur at higher altitudes or in arid regions are locally migratory. Its habitat is dry deciduous forests, where it is mostly solitary. It is called Hawk-cuckoo as it resembles a sparrow hawk.
The adult is about the size of a pigeon (13.4 inches). The plumage is ash-gray above, whitish below, and cross-barred with brown. It has a broadly barred tail. Sexes are similar. When flying into trees and landing, it shakes its tail from side to side much like a sparrow hawk. During the summer months, the call is easily detected by its repeated screaming dee dee dit calls. This call is heard all throughout the day and frequently during moonlit hours.
Common Hawk-cuckoos feed on hairy caterpillars and other insects, berries and wild figs. Like many other cuckoos, this species is a brood parasite, the female lays a single egg in the nest of other birds, mostly babblers. It breeds from March to June, coinciding with that of babblers. The egg is blue, like that of the host. The hatchling pushes the eggs of its host out of the nest and is reared to maturity by foster parents.