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run circles around

Hammerkop

[ham-er-hed]
The Hammerkop (Scopus umbretta), also known as Hamerkop, Hammerhead, Hammerhead Stork, Umbrette, Umber Bird, Tufted Umber, or Anvilhead, is a medium-sized wading bird (56 cm long, weighing 470 g). The shape of its head with a curved bill and crest at the back is reminiscent of a hammer, hence its name.

Description

Its plumage is a drab brown with purple iridescence on the back. The bill is long, flat, and slightly hooked. It looks similar to those of the Shoebill and the Boat-billed Heron, probably because of convergent evolution. The neck and legs are shorter than those of most of the Ciconiiformes. The Hammerkop has partially webbed feet, for unknown reasons. It middle toe is comb-like (pectinated) like a heron's. Its tail is short and its wings are big, wide, and round-tipped; it soars well. When it does so, it stretches its neck forward like a stork or ibis, but when it flaps, it coils its neck back something like a heron.

Vocalisations include cackles and a shrill call given in flight. Hammerkops are mostly silent except when in groups.

Range and habitat

The Hammerkop occurs in Africa south of the Sahara, Madagascar and coastal southwest Arabia in all wetland habitats, including irrigated land such as rice paddies, as well as in savannas and forests. Most remain sedentary in their territories, which are held by pairs, but some move into suitable habitat during the wet season only. Whenever people create new bodies of water with dams or canals, Hammerkops move in quickly.

Feeding

Hammerkops feed during the day, often taking a break at noon to roost. They normally feed alone or in pairs. The food is typical of long-legged wading birds, and the most important is Xenopus tadpoles and frogs. They also eat insects, shrimp, fish, rodents and similar small animals. They walk in shallow water looking for prey, possibly raking their feet on the bottom or suddenly opening their wings to flush prey out of hiding. They may also take prey while they fly, particularly tadpoles.

Social behavior and reproduction

The Hammerkop's behavior is unlike other birds'. One unusual feature is that up to ten birds join in "ceremonies" in which they run circles around each other, all calling loudly, raising their crests, fluttering their wings. Another is "false mounting", in which one bird stands on top of another and appears to mount it, but they may not be mates and do not copulate.

The strangest aspect of Hammerkop behavior is the huge nest, sometimes more than 1.5 m across, comprising perhaps 10,000 sticks and strong enough to support a man's weight. The birds decorate the outside with any bright-coloured objects they can find. When possible, they build the nest in the fork of a tree, often over water, but if necessary they build on a bank, a cliff, a human-built wall or dam, or on the ground. A pair starts by making a platform of sticks held together with mud, then builds walls and a domed roof. A mud-plastered entrance 13 to 18 cm wide in the bottom leads through a tunnel up to 60 cm long to a nesting chamber big enough for the parents and young.

These birds are compulsive nest builders, constructing 3 to 5 nests per year whether they are breeding or not. Barn Owls and eagle owls may force them out and take over the nests, but when the owls leave, the Hammerkops may reuse the nests. Snakes, small mammals such as genets, and various birds live in abandoned nests, and weaver birds, mynas, and pigeons may attach their nests to the outside.

At the finished nest, a pair gives displays similar to those of the group ceremonies and mates, often on top of the nest. The clutch consists of 3 to 7 eggs that start white but soon become stained. Both sexes incubate for 28 to 30 days. Both feed the young, often leaving them alone for long times; this unusual habit for wading birds may be made possible by the thick nest walls. The young hatch covered with gray down. By 17 days after hatching, their head and crest plumage is developed, and in a month, their body plumage. They leave the nest at 44 to 50 days but roost in it at night until about two months after hatching.

Systematics

The Hamerkop is usually included in the Ciconiiformes, but might be closer to the Pelecaniformes. It constitutes a family (Scopidae) and genus (Scopus) all on its own because of its unique characteristics.

Culture

There are many legends about the Hammerkop. In some regions, people state that other birds help it build its nest. The Xam informants of Wilhelm Bleek said that when a Hammerkop flew and called over their camp, they knew that someone close to them had died. It is known in some cultures as the lightning bird, and the Kalahari Bushmen believe or believed that when anyone was hit by lightning, it resulted from trying to rob a Hammerkop's nest. They also believe that the inimical god Khauna would not like anyone to kill a Hammerkop. According to an old Malagasy belief, anyone who destroys its nest will get leprosy, and a Malagasy poem calls it an "evil bird". Such beliefs have given the bird some protection.

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