Birds
Hamerkop
Scopus umbretta · also called hamerkop, hammerkop, hammerhead stork, anvilhead
The hamerkop is a modest brown wading bird with a hammer-shaped head and an outsized obsession: it builds the biggest nest of any bird for its size — a domed stick fortress a metre and a half across that can bear the weight of a grown adult, and it builds several every year whether it needs them or not.
Overview
Hamerkops live across sub-Saharan Africa, Madagascar, and southwestern Arabia, beside almost any shallow fresh water, including farm dams and roadside ditches. They are about 56 cm, plain brown, with a thick backward crest and heavy bill that together make the “hammer.” They hunt frogs, tadpoles, small fish, and aquatic insects, shuffling through the shallows to stir up prey.
The nest
The hamerkop’s nest is a roofed dome of thousands of sticks bound with mud, over a metre wide, with a narrow entrance tunnel to an inner chamber. It can weigh 25–50 kg and hold a person’s weight. A pair takes weeks to build one and often decorates it with bright rubbish, bone, and dung.
Serial builder
Pairs build three to five large nests a year, breeding or not, and dozens over a lifetime. Abandoned nests are prime real estate, taken over by owls, kestrels, geese, genets, snakes, monitor lizards, and bees — sometimes before the hamerkops finish.
An odd bird
The hamerkop is the only species in its family; its closest relatives are the shoebill and pelicans. Across Africa it is widely regarded as a bird of ill omen — the “lightning bird” — and folklore that harming its nest brings disaster has helped protect it.
Status
The hamerkop is Least Concern, common and adaptable, affected locally by wetland drainage and pesticides.
Hamerkop: common questions
Why does the hamerkop build such an enormous nest?
No one is certain, because the nest is far larger and stronger than the small bird strictly needs to raise its two to four chicks. It is a roofed dome, typically over a metre wide, made from thousands of sticks bound with mud, with a narrow entrance tunnel leading to an inner chamber — solid enough that a grown person can stand on top of one. Ideas for why include protection — the thick walls and small, low doorway keep out most predators and shade the eggs from the fierce sun. It may also be sexual and social display — hamerkop pairs build compulsively, add nests around their territory, and perform noisy group ceremonies at them — so a big, well-made nest could advertise the quality of the pair. The building behaviour seems partly instinctive and hard to switch off.
How many nests does a hamerkop build?
A pair typically builds three to five large nests per year, and over a lifetime may make fifty or more, only a fraction of which are ever used for eggs. They build in the breeding season and outside it, and they keep adding material to and repairing nests they are not using. The nests are often decorated with brightly coloured or shiny objects the birds collect — plastic, cloth, bone, animal dung, bits of metal. Because sturdy, roofed nests are valuable real estate, abandoned hamerkop nests are quickly claimed by a long list of other animals — eagle owls and barn owls, kestrels, Egyptian geese, grey kestrels, snakes, monitor lizards, genets, mongooses, bees, and more. Some birds evict the hamerkops before they have even finished.
Is the hamerkop a stork or a heron?
Neither, although it looks like a small brown stork and was long placed near them. Modern genetic and anatomical evidence puts the hamerkop in its own family, Scopidae, with its closest living relatives being the shoebill and the pelicans, and the herons and the ibises a little further out. It shares with the shoebill an oddly shaped heavy bill and a preference for hunting amphibians in shallow water. The hamerkop has some heron-like features too, such as powder-down feathers and a comb-like claw for grooming, which is part of why its classification took so long to settle.
Why is the hamerkop considered unlucky or magical in African folklore?
The hamerkop features in the traditions of many African peoples, usually with a supernatural or ominous character. In parts of southern Africa it is called the "lightning bird" and associated with witchcraft, storms, and death; some Khoisan and Malagasy traditions say that anyone who robs or damages a hamerkop nest will be struck by lightning, have their house burn down, or suffer some other disaster, and that the bird can foretell death by flying over a homestead and calling. The San regard it with particular respect. Whatever the origin of these beliefs, their practical effect has been protective — people across the continent leave hamerkops and their conspicuous nests alone, which is one reason the bird thrives close to human settlement.