Hammerheads

(Scopidae)

Class Aves

Order Ciconiiformes

Suborder Scopi

Family Scopidae

Thumbnail description
Large uniform-brown wading bird with a distinctive large, backward-pointed crest

Size
Length: 20–24 in (50–60 cm); wing: 11.6–12.4 in (297–316 mm); weight: 0.91–0.95 lb (415–430 g)

Number of genera, species
1 genus; 1 species

Habitat
Most freshwater habitats, even small temporary ponds

Conservation status
Not threatened; common in appropriate habitat

Distribution
Sub-Saharan Africa: Senegal to southern Somalia south to southern South Africa; Madagascar, and southwest Arabian Peninsula

Evolution and systematics

The origins of the hamerkop or hammerhead (Scopus umbretta) are obscure. Discovered by Gmelin in Senegal, Africa, in 1789, it has been traditionally placed in the Ciconiiformes with other large, long-legged, wading birds.

The hammerhead shares affinities with different groups. It shares a pectinated claw on the middle toe with herons; it shares a free hind toe with flamingos; and its ectoparasites are related to those of plovers. Its egg-white proteins place it close to the storks; DNA suggests that it should be between the herons and flamingos, close to the storks.

It is distinctive enough that it has been placed in its own suborder Scopi.

Physical characteristics

There are two subspecies, which vary in size and appearance. In the nominate race (S. u. umbretta), the hammerhead stands about 22 in (56 cm) tall; the more restrictive West African race (S. u. minor) is smaller and darker. The entire body is dull brown, paler on the chin and throat. The head is strongly crested, and the crest points backward. The crest and the long, heavy bill suggest the name "hammerhead." The female is similar to the male but slightly larger.

Distribution

The species is found in sub-Saharan Africa from Senegal in the west, east to southern Somalia and south to southern South Africa. It is also found in Madagascar and the southwest Arabian Peninsula.

The hammerhead is nonmigratory, although in drier areas there may be some seasonal dispersal as rains lead to additional temporary feeding sites.

The nominate race (S. u. umbretta) is found through most of the range in tropical Africa, Madagascar, and the southwest Arabian peninsula. The West-African race (S. u. minor) is found in the coastal belt from Sierra Leone to eastern Nigeria.

Habitat

The hammerhead is found in almost all types of wetlands. For feeding it requires shallow wetlands from lakeshores to the banks of large rivers to small temporary ponds.

For breeding, the species requires a foundation to support its large, complicated nest. Both male and female hammerheads participate in building nests, which can weigh 100 times more than the bird. Almost always these are located in large trees but rarely cliffs or rocky hillsides are used. These areas are also used for roosting.

Behavior

Hammerheads are generally active during the day or are crepuscular, but are not active at night as some have suggested. As with other tropical birds, they are less active during the heat at mid-day. They are usually found alone or in small groups, though occasionally large groups (up to 50 birds) may roost together.

Feeding ecology and diet

Hammerheads feed by wading in shallow water and picking prey from among vegetation. They may stir the water with their feet ("foot stirring") or open their wings ("wing flicking") to encourage prey to move. They also capture prey while flying, often catching tadpoles or small fish when in small pools. They can fly slowly over the water because they have low wing loadings (i.e., large wing area compared to low mass).

Their major prey varies geographically. They are particularly known for taking clawed frogs (Xenopus sp.) or their tadpoles in south and east Africa. In other areas (e.g., Mali), they concentrate on small fish. They also take shrimp, crustaceans, and even small mammals.

Reproductive biology

Hammerheads are monogamous and territorial, although territories often overlap. The breeding time varies geographically, but is primarily in the dry season or late in the wet season. At this time, decrease in water leads to a concentration of prey, making it easier for the adults to collect adequate food for their young.

They are famous for their very large and elaborate nests. The domed nests may include over 8,000 items, be as much as 5 ft (1.5 m) deep, weigh up to 55 lb (25 kg), and fully support an adult man or woman. The materials include mostly sticks, leaves, and mud. The structures include a chamber up to 16 in (40 cm) wide and 24 in (60 cm) high, and an entrance 4–6 in (10–15 cm) in diameter and 16–24 in (40-60 cm) long. Nests are most often built in a fork in a tree, usually about 30 ft (9 m) above the ground, but occasionally on cliffs or rarely on the ground.

Both members of a pair share in nest construction, often working together. Working primarily in the morning and evening, they construct the nest platform, followed by the walls, and then the roof.

While a nest may be used for one or many seasons, a pair may build 3–5 nests in a single season. Some are abandoned before completion; some are used for roosting; one may be used for breeding, or other animals may take advantage of these nests. Other animals observed using nests, include: Verreaux's eagle owl (Bubo lacteus), barn owl (Tyto alba), Egyptian goose (Alopochen aegyptiacus), genets (Genetta spp.) monitor lizard (Veranus spp.), and spitting cobra (Naja nigricollis).

After the nest is complete, three to seven white eggs, measuring 1.6–2.1 in by 1.3–1.5 in (41–53 mm by 32–37 mm) and

weighing about 1 oz (25 g) are laid in one to two day intervals. Both parents incubate and care for the young. Hatching occurs after about 30 days following the completion of the clutch. At hatching, the downy young are pale brown. They begin fledge at about 50 days old.

Conservation status

The hammerhead is common to abundant throughout its range.

Significance to humans

Throughout much of its range, it is considered a bird with supernatural powers and even evil powers. It is thought that if improperly treated, a hammerhead can cause a house to melt, an epidemic among cattle, or even death. It has been given great respect and distance.

This respect may be due to the bird's strange appearance, its gigantic nest, and the many other birds and animals that may occupy abandoned nests, including deadly cobras.

Resources

Books

Brown, L.H., E.K. Urban, and K. Newman. The Birds of Africa. Vol. 1, Ostrich to Falcons. London: Academic Press, 1982.

del Hoyo, J., A. Elliott, and J. Sargatal, eds. Handbook of the Birds of the World. Vol. 1, Ostrich to Ducks. Barcelona: Lynx Edicions, 1992.

Hancock, J.A., J.A. Kushlan, and M.P. Kahl. Storks, Ibises and Spoonbills of the World. London: Academic Press, 1992.

Maclean, G.L. Roberts' Birds of Southern Africa. 5th ed. London: New Holland Publishers, 1985.

Wilson, R.T., and M.P. Wilson. Breeding Biology of the Hamerkop in Central Mali. Proceedings of the Fifth Pan-African Ornithological Congress, edited by J. Ledger.

Periodicals

Liversidge, R. "The Nesting of the Hamerkop, Scopus umbretta." Ostrich 34 (1963): 55-62.

Wilson, R.T. "Nest Sites, Nesting Seasons, Clutch Sizes and Egg Sizes of the Hamerkop Scopus umbretta." Malimbus 9(1987): 17-22.

Wilson, R.T., M.P. Wilson, and J.W. Durkin. "Aspects of the Reproductive Ecology of the Hamerkop Scopus umbretta in Central Mali." Ibis 129 (1987): 382-388.

Malcolm C. Coulter, PhD