The Green Ibis, Mesembrinibis cayennensis, is a wading bird in the ibis family Threskiornithidae. It is the only member of the genus Mesembrinibis.

This is a resident breeder from Honduras through Nicaragua, Costa Rica and western Panama, and South America to northern Argentina. It undertakes some local seasonal movements in the dry season.

The Green Ibis occurs in wooded swamps and other wet forest habitats. Its nest consists of a platform of twigs placed in a tree. This species is less gregarious than its relatives and is usually seen alone or in pairs. It has been recorded as harassing Sunbitterns nesting in the same tree.

Like other ibises, it predates fish, frogs and other water creatures, as well as insects. it is most active and vocal at dusk, with a loud rolling co-co-co-co-corru-corru call.

The Green Ibis is 48-56 cm long and weighs 650-750 g; the female is smaller than the male. Breeding adults have glossy greenish-black bodies, pale green legs and bill, and grey bare facial skin patches. Juveniles are much duller, but can be distinguished from the similar Glossy Ibis by their bulkier shape, shorter legs and broader wings. This species, like other ibises, flies with neck outstretched. Its flight is heavy, with fewer glides and jerkier wingbeats than its relatives.

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