Harpy eagle

Name and taxonomy

Carl Linnaeus described the bird in 1758 and placed it among the vultures. He borrowed the name from the harpies of Greek myth. Louis Pierre Vieillot set up the genus Harpia in 1816. The harpy eagle is still the only species in that genus. English writers add American to the name to separate it from the Papuan eagle.

Four birds make up the subfamily Harpiinae. They are the harpy eagle, the crested eagle, the Papuan eagle and the bat hawk. The Philippine eagle was once thought to be a close relative. DNA has since moved it to a different branch of the raptor family. The two birds probably look alike because they hunt in the same way.

Evolution and relatives

The harpy eagle sits within the hawk and eagle family Accipitridae. Its nearest living relative is the crested eagle of the same forests. The crested eagle is far lighter and probably takes much smaller prey. The Papuan eagle appears to fill a similar role on the other side of the world.

The wings are short and very broad for a bird of this size. That shape turns tightly between trunks and branches. Eagles of open country, such as the sea eagles, span far more. The extinct Haast's eagle of New Zealand was larger than any eagle alive. A live harpy eagle stood in for that extinct bird in a television series.

Appearance

Total length runs 86.5 to 107 cm and the wings span 176 to 224 cm. The tail measures 37 to 42 cm and works as a rudder in flight. Females weigh 6 to 9 kg and males 4 to 6 kg. A captive female named Jezebel reached 12.3 kg. Wild birds probably never grow that heavy, because food is harder to get.

The upper parts are slate black and the belly is white. A broad black band crosses the chest below the pale grey head. The feathered legs are striped black and white. A double crest of long black feathers rises when the bird is alarmed. Some researchers suggest the raised crest also gathers sound towards the ears. Males and females wear exactly the same pattern.

The feet are arguably the most striking part of the bird, as with other eagles. The lower leg reaches up to 13 cm long and is as thick as a human wrist. A female's rear talon averages 12.3 cm, and a male's 8.6 cm. Those claws match a grizzly bear's in length. The toes are yellow and the bill and claws are black.

Habitat and range

The range starts in southern Mexico and reaches northern Argentina. Brazil holds the most birds, spread across the whole country. In Central America only parts of Panama and Costa Rica still hold a real population. The species has gone from El Salvador altogether. GBIF holds records from 25 countries.

The bird wants tropical lowland rainforest with very tall trees. It hunts and nests in the emergent layer above the main canopy. Most records fall below 900 metres, but a few reach 2,000 m. Harpy eagles avoid disturbed ground and keep away from people. They will cross forest edge, pasture and even farmland on a hunting trip. Loss of tall trees is likely to shrink the range further.

Diet and hunting

A review of the literature and camera traps lists 116 prey species. Tree mammals make up almost all of it. At one Brazilian nest, sloths of two species accounted for 79% of the prey. Monkeys came to about 37% of the remains at nests in Guyana. Capuchins, sakis, howlers, woolly monkeys and spider monkeys are all taken. Tamarins and marmosets appear to be too small to bother with.

Porcupines, anteaters, armadillos, coatis, kinkajous and opossums fill out the list. Macaws, curassows and other large birds are taken now and then. One young male learned to kill black vultures and did so repeatedly. Iguanas and snakes appear in the diet in some regions. Chickens, lambs and young pigs are taken very rarely.

Perch hunting is the usual method. The eagle moves between trees, watching, then drops onto prey it has spotted. It will also wait for hours above a river or a salt lick. Sometimes it chases a bird through the branches, twisting between trunks. Prey averages about 2.6 kg, and a female can lift 6 to 9 kg without landing. A harpy eagle need not feed daily, and it can last a week between meals.

Behaviour and social life

Harpy eagles live in pairs and hunt alone. A pair holds a territory of roughly 30 square kilometres. They drive out any other harpy eagle that enters it. In good forest, active nests can sit only 3 km apart. In broken forest, territories stretch to about 25 km across.

The birds hunt by day and rest at night. One bird has been recorded sitting on a perch for up to 23 hours while watching. That patience seems to suit a forest where prey is scattered. A pair is often seen with a third bird, their young from the last brood. During nest building the pair rarely goes more than 180 metres from the tree. Adults will attack a person who climbs towards the nest.

Communication and senses

Away from the nest the harpy eagle is almost silent. At the nest the adults give a thin, drawn-out wailing scream. The female's version of that call is lower in pitch than the male's. A male arriving with food adds fast chirps and goose-like notes.

The parents call less as the chick grows, and the chick calls more. A nestling gives a repeated chi-chi-chi when rain or sun reaches it. Nestlings croak, quack and whistle when a person approaches. Perched adults produce a long wailing note that is probably territorial. A pair rubs bills together, which appears to maintain the bond. Sight leads the senses, with hearing close behind in dense cover.

Reproduction and life cycle

Pairs are thought to stay together for life, over 25 to 30 years. No courtship display has been described for the species. The nest is a platform of woven sticks lined with soft plants and fur. It measures about 1.2 metres deep and 1.5 m across. The pair sets it 16 to 43 m above the ground, in the main fork of a tall tree. Kapok and Brazil nut trees are favourites, and a nest serves for years.

The female lays two white eggs at the start of the rains. Only the first chick is raised, and the second egg is left to fail. Incubation runs about 56 days, mostly by the female. The male brings in most of the food during that time. The chick stands and walks awkwardly at 36 days old.

It leaves the nest at about six months. The parents keep feeding it for another 6 to 10 months after that. A young bird often stays inside its parents' territory for a year. Breeding maturity comes at 4 to 6 years old. A pair raises one chick every 2 to 3 years, which is a very slow rate. A healthy adult may live 25 to 35 years.

Predators and threats

No animal hunts a healthy adult harpy eagle. The species sits at the top of the rainforest food chain. A nestling is very occasionally taken by another harpy eagle. The parents guard the nest tree and usually prevent that. Disease and injury matter more, because a hurt bird cannot catch prey.

The real threat is people. Logging, cattle ranching, farming and prospecting all remove the tall forest. Farmers shoot the bird as a supposed danger to stock and to children. One scientifically documented attack on an adult woman exists. Its size and its lack of fear make it an easy target for a hunter. A warming climate is expected to shrink the remaining habitat further.

Population and conservation

The IUCN rates the harpy eagle as Vulnerable, and the population is falling. CITES places the bird on Appendix I, its strictest list. In Mexico and Central America the species counts as critically endangered. Mexican birds once reached Veracruz and now hold on only in Chiapas. Naturalists have logged just 1,630 sightings on iNaturalist.

Brazil holds the core of what remains. Even there the bird has almost gone from the Atlantic forest. State assessments call it critically endangered in Sao Paulo and Parana. Researchers now monitor 62 known nest sites in Brazil, nearly all in Amazonia. Local volunteers do much of that watching, alongside satellite tracking.

Captive breeding has put birds back into empty forest. The Peregrine Fund started a breeding programme in 1989. It opened a raptor centre in Panama in 2001. Since 1998, close to 50 birds have gone back into the forest in Panama and Belize. Belize began its own restoration project in 2003 with the Belize Zoo. A bird named Hope, the 15th released there, went out in December 2009.

Relationship with humans

Most people inside the range probably never see a harpy eagle. The bird avoids settlement and keeps to unbroken forest. It takes livestock so rarely that the loss is trivial. Even so, farmers shoot birds they believe are a danger. Education programmes now target that belief directly.

Indigenous hunters have used harpy eagle feathers in ceremonies. Trade in the birds is illegal, and confiscated eagles are released again. Costa Rica and Panama both draw visitors who hope to see one. Protecting a pair protects a very large block of forest around them. Conservationists therefore treat the eagle as an umbrella species.

In culture and myth

The name comes from Greek myth. The harpies were half woman and half bird, and Thaumas and Electra were their parents. Their names carried meanings such as storm swift and the dark. They acted as the hounds of Zeus and carried off wrongdoers. Their best known task was stealing food from King Phineus of Thrace. Hesiod drew them as winged maidens, while Ovid called them human-vultures.

The bird is the national bird of Panama and appears on the national arms. Panama gave it that status in 2002, after a public education campaign. It also served as the state bird of Parana in Brazil. Venezuela printed the eagle on the back of one of its banknotes.

Aztec worship treated the harpy eagle as a bird of Quetzalcoatl. Many South American cultures treat felling a kapok tree as bad luck. That belief may protect the very trees the eagle nests in. Film designers used the bird as the model for a phoenix in a fantasy series. Few living birds, probably, have lent their shape to so many invented ones.