Hamerkops are widely dispersed throughout sub-Saharan Africa. They live in diverse habitats, from forest to semi-desert, anywhere where water is accessible. They frequent lakes, rivers, marshes, temporary seasonal ponds, and man-made waterways such as dams and irrigation channels. Hamerkops are most often seen in savannahs and woodlands, and may be only seasonally resident in semi-arid areas. They can be seen in the African Aviary exhibit of the Maryland Zoo.
Individual hamerkops occupy well-defined territories that they rarely leave. They normally occur in pairs, but can gather in social groups of up to 50 birds, although usually closer to 10.
Like storks and herons, hamerkops are wading birds that forage for food in shallow water. They feed mainly on frogs and fish. They may stir the water with their feet or flap their wings to startle prey. Hamerkops also feed in flight, gliding over open water and dipping down to grab fish. Hamerkops are good hunters, but often get robbed of their prey by bigger birds like the Fish Eagle so must catch many fish to satisfy their appetite.
Hamerkops are most distinguished by their huge, domed nests. They build the biggest nests of any bird in Africa! Pairs build the nest together, collecting many thousand twigs and other items to build it. A finished nest may contain as many as 8,000 items and weigh at least 25 kg. Although enormous itself, the nest is accessibly only by a small, narrow entrance hole.
These nests attract many other species of wildlife. Verreaux’s eagle owls, Gray kestrels, and barn owls sometimes take over hamerkop nests, evicting the rightful residents. Smaller mammals such as gennets sometimes take up residence in hamerkop nests, as do other species of bird such as weaver birds, mynas, and pigeons that will attach their own smaller nests to the main nest. Monitor lizards and snakes often raid hamerkop nests to take eggs, and snakes may stay behind to occupy the nests as shelter. Old nests are quickly occupied by other hole-nesting birds such as the Egyptian goose, the Pygmy goose, or the Knob-billed duck. By their nests, hamerkops make it possible for several other species of bird to find suitable breeding sites where they wouldn’t otherwise.
A high percentage of eggs and chicks are taken by predators such as monitor lizards and snakes. An estimated 50% of all eggs and 30-40% of chicks are lost to predation. Chances of survival increase considerably with age, and the hamerkop is actually a long-lived bird. The mean adult lifespan is about 20 years.
Hamerkops often gather near nesting sites for social courtship displays. Many birds start calling all at once while running around each other in circles with crests raised and wings fluttering. Males may pretend to mate with females during this courtship display, but it’s only ceremonial. Actual mating between pair occurs during nest-building and after nest is complete.
Female lays 3-7 eggs and male and female take turns sitting on the eggs during the incubation period, which lasts about 30 days. Both parents help feed the chicks once they hatch out. Chicks are ready to fly after about 50 days. They continue to return to the nest for two weeks after first flight, and may roost together in the nest for another month before dispersing.
Hamerkops are an abundant species that adapt well to any aquatic environment. They are rarely persecuted by people because traditional folklore contends that these birds have magical powers.