Hamerkop
The hamerkop, also called the umbrette, is a medium-sized bird. It is the only living species in the genus Scopus and the family Scopidae. The species and family was long thought to sit with the Ciconiiformes but is now placed with the Pelecaniformes, and its closest relatives are thought to be the pelicans and the shoebill. The shape of its head with a long bill and crest at the back is reminiscent of a hammer, which has given this species its name after the Afrikaans word for hammerhead. It is a medium-sized waterbird with brown plumage. It is found in mainland Africa, Madagascar and Arabia, living in a wide variety of wetlands, including estuaries, lakesides, fish ponds, riverbanks, and rocky coasts. The hamerkop is a sedentary bird that often shows local movements.
The hamerkop takes a wide range of prey, mostly fish and amphibians, but shrimps, insects and rodents are taken too. Prey is usually hunted in shallow water, either by sight or touch, but the species is adaptable and will take any prey it can. The species is renowned for its enormous nests, several of which are built during the breeding season. Unusually for a wading bird, the nest has an internal nesting chamber where the eggs are laid. Both parents incubate the eggs and raise the chicks.
The species is not globally threatened and is locally abundant in mainland Africa and Madagascar. The International Union for Conservation of Nature has assessed it as being of least concern.
Taxonomy and systematics
The hamerkop was first described by the French zoologist Mathurin Jacques Brisson in 1760 in his landmark Ornithologia, which was published two years after the tenth edition of Carl Linnaeus' Systema Naturae. The species was subsequently described and illustrated by French polymath Comte de Buffon. When the German naturalist Johann Friedrich Gmelin revised and expanded Linnaeus's Systema Naturae in 1788 he included the hamerkop and cited the earlier authors. He placed the species in the genus Scopus that had been introduced by Brisson and coined the binomial name Scopus umbretta.Brisson's names for bird genera were widely adopted by the ornithological community despite the fact that he did not use Linnaeus' binomial system. The International Commission on Zoological Nomenclature ruled in 1911 that Brisson's genera were available under the International Code of Zoological Nomenclature, so Brisson is considered to be the genus authority for the hamerkop. The generic name, Scopus, is derived from the Ancient Greek for "shadow". The specific name umbretta is modified from the Latin for "umber" or "dark brown".
The hamerkop is sufficiently distinct to be placed in its own family, although the relationships of this species to other families has been a longstanding mystery. The hamerkop was usually included in the Ciconiiformes, but is now thought to be closer to the Pelecaniformes. Recent studies have found that its closest relatives are the pelicans and shoebill. Although the hamerkop is the only living member of its family, one extinct species is known from the fossil record. Scopus xenopus was described by ornithologist Storrs Olson in 1984 based on two bones found in Pliocene deposits from South Africa. Scopus xenopus was slightly larger than the hamerkop and Olson speculated based on the shape of the tarsus that the species may have been more aquatic.
The hamerkop is also known as the hammerkop, hammerkopf, hammerhead, hammerhead stork, umbrette, umber bird, tufted umber, or anvilhead.
Subspecies
Two subspecies are recognized—the widespread nominate race S. u. umbretta and the smaller of West African S. u. minor, described by George Latimer Bates in 1931. Two other subspecies have been proposed. S. u. bannermani of south-west Kenya is usually lumped with the nominate race. Birds in Madagascar have been suggested to be distinct, in which case they would be placed in the subspecies S. u. tenuirostris. That proposed subspecies was described by Austin L. Rand in 1936. It has also been suggested that birds near the Kavango River in Namibia may be distinct, but no formal description has been made.Description
The hamerkop is a medium-sized waterbird, standing high and weighing, although the subspecies S. u. minor is smaller. Its plumage is a drab brown with purple iridescence on the back; S. u. minor is darker. The tail is faintly barred with darker brown. The sexes are alike and fledglings resemble adults. The bill is long,, and slightly hooked at the end. It resembles the bill of a shoebill, and is quite compressed and thin, particularly at the lower half of the mandible. The bill is brown in young birds, but becomes black by the time a bird fledges.The neck and legs are proportionately shorter than those of similar looking Pelecaniformes. The bare parts of the legs are black and the legs are feathered only to the upper part of the tibia. The hamerkop has, for unknown reasons, partially webbed feet. The middle toe is comb-like like a heron's. Its tail is short and its wings are big, wide, and round-tipped; it soars well, although it does so less than the shoebill or storks. 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. Its gait when walking is jerky and rapid, with its head and neck moving back and forth with each step. It may hold its wings out when running for extra stability.
Distribution and habitat
The hamerkop occurs in Africa south of the Sahara, Madagascar, and coastal south-west Arabia. It requires shallow water in which to forage, and is found in all wetland habitats, including rivers, streams, seasonal pools, estuaries, reservoirs, marshes, mangroves, irrigated land such as rice paddies, savannahs, and forests. In Tanzania, it has also recently begun to feed on rocky shores. In Arabia, it is found in rocky wadis with running water and trees. Most are sedentary within their territories, which are held by pairs, but some migrate into suitable habitat during the wet season only. The species is very tolerant of humans and readily feeds and breeds in villages and other human-created habitats.Behaviour and ecology
The hamerkop is mostly active during the day, often resting at noon during the heat of the day. They can be somewhat crepuscular, being active around dusk, but are not nocturnal as has sometimes been reported.Social behaviour and calls
The hamerkop is mostly silent when alone, but is fairly vocal when in pairs or in groups. The only call it usually makes when alone is a flight-call, a shrill "nyip" or "kek". In groups, vocalisations include a range of calls including cackles and nasal rattles. One highly social call is the "yip-purr" call. This call is only made in a social context, when at least three birds, but up to 20 are gathered in a flock. Birds start by giving a number of "yip" calls, eventually giving way to purring notes. This call is made with the neck extended and sometimes accompanied by wing flapping, and becomes more vigorous when larger numbers of birds are present.Another common social behaviour is "false mounting", in which one bird stands on top of another and appears to mount it, but they do not copulate. This behaviour has been noted between both mated pairs and unmated birds, and even between members of the same sex and in reversed mountings, where females mount males. Because of this, the behaviour is thought to be social and not related to the pair bond. Dominant birds may signal to subordinates by opening their bills slightly and erecting their crests, but the species is not very aggressive in general towards others of its species. Birds in groups also engage in social allopreening. One bird presents its face of back of the head to the other to be preened.
Food and feeding
This species normally feeds alone or in pairs, but also feeds in large flocks sometimes. It is a generalist, although amphibians and fish form the larger part of its diet. The diet also includes shrimp, insects, and rodents. The type of food they take seems to vary by location, with clawed frogs and tadpoles being important parts of the diet in East and Southern Africa and small fish being almost the only prey taken in Mali. Because it is willing to take a wide range of food items and also take very small prey, it is not resource-limited and only feeds for part of the day.The usual method of hunting is to walk in shallow water looking for prey. Prey is located differently depending on circumstances; if the water is clear, it may hunt by sight, but if the water is very muddy, it probes its open bill into water or mud and shuts it. It may shuffle one foot at a time on the bottom or suddenly open its wings to flush prey out of hiding. Prey caught in mud is shaken before swallowing to clean it, or if available, taken to clearer water to do so. The species also feeds while in flight. A bird flies slowly low over the water with legs dangling and head looking down, then dipping feet down and hovering momentarily when prey is sighted. The prey is then snatched with the bill and swallowed in flight. This method of hunting can be very successful, with one birds catching prey on 27 of 33 attempts during one 45-minute session. It is also opportunistic, and feeds on swarming termites when they conduct their nuptial flights, snatching as many as 47 alates in five minutes.
This species has been recorded foraging for insects flushed by grazing cattle and buffalo, in a manner similar cattle egrets, and has been observed fishing off the backs of hippopotamuses. It has also been recorded feeding in association with banded mongooses; when a band of mongooses began hunting frogs in dried mud at the side of a pool of water a pair of hamerkops attended the feeding group, catching frogs that escaped the mongooses.