Red-billed hornbill (Tockus erythrorhynchus)—Mark BoultonThe National Audubon Society Collection/Photo Researchers
Any of 54 species of Old World tropical birds (family Bucerotidae) noted for the bony helmet on the bill of some species. Hornbills range from 16 to 63 in. (40 to 160 cm) long and typically have a large head, prominent bill, thin neck, broad wings, long tail, and brown or black plumage, usually with bold white markings. They nest in cavities, usually in large trees. The male of most species walls up the female in the nest, closing the hole with mud, except for a small opening through which he passes food. The female breaks out after the eggs hatch, but the young may be walled up again.