ibis (ī'bĭs) , common name for wading birds with long, slender, decurved bills, found in the warmer regions of both hemispheres. The body is usually about 2 ft (61 cm) long. Most ibises nest in colonies. They feed in ponds, lakes, and brackish marshes on fish and other aquatic animals. Ibises are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Ciconiiformes, family Threskiornithidae.