Papuan eagle

The Papuan eagle (Harpyopsis novaeguineae) is a large bird of prey. It is also known by several other names, including Papuan harpy eagle, New Guinea eagle, New Guinea harpy eagle, or kapul eagle, the latter name from the local name for a usually arboreal marsupial that the eagle is known to regularly hunt. This is an endemic species to New Guinea, and it can occasionally be found throughout the island. This is a forest-dwelling species, usually occurring in mature rainforest. The Papuan eagle is a fairly little-known species for a large eagle; however, it is known to prey on a wide range of prey, probably by and large mammals and birds from small to quite large sizes. Unique amongst eagles, the Papuan eagle is a surprisingly fast and agile terrestrial avian predator and is capable of chasing down prey on the forest floor. What little study has been conducted about its breeding habits suggests it nests in a large forest tree, perhaps every other year. The Papuan eagle is probably naturally scarce, but it is under the threat of habitat destruction by deforestation, as well as hunting. Due to its small and declining population, the species has been classified as vulnerable by the IUCN.

The New Guinea eagle is a fairly large eagle and very large raptor. Though the sexes are similar, the female is slightly larger than the male, with a range up to a 34% size difference. In total length, adults range from 75 to 90 cm (30 to 35 in). The relatively short but broad wingspan, as expected in forest-dwelling raptors, is 121 to 157 cm (4 ft 0 in to 5 ft 2 in). The body mass widely reported is relatively light for so large a raptor at 1.6 to 2.4 kg (3.5 to 5.3 lb). This may be due in no small part to its extremely long tail, which measures 384 to 394 mm (15.1 to 15.5 in) in males and 410 to 435 mm (16.1 to 17.1 in) in females. The weights reported according to some authors probably underrepresent their size, especially those of full-grown females, and their body size range based on linear dimensions (the weighed birds could have been all smaller males). This species also possesses an exceptional long tarsus, which may rival the Philippine eagle, which weighs about three times more than the Papuan eagle, as the longest of all living eagles at 123 to 145 mm (4.8 to 5.7 in). Meanwhile, the wing chord measures 368 to 442 mm (14.5 to 17.4 in) in males and 450 to 494 mm (17.7 to 19.4 in). A single male had a culmen length of 48 mm (1.9 in).

At all ages, Papuan eagles are a greyish brown raptor with a creamy-coloured underside. Adults also have obscure darker bars on the underside. The back bears faint buff and white edging, which in good light can make these areas appear somewhat scaled. The tail is of the same colour as the back with a whitish tip with four or five blackish bands (the subterminal one being broad), which are also present on the cream-colored undertail. The juvenile is similar to the adult, but is of a slightly paler grey-brown colour above with a slightly more buff colouring on the underside. Also, the juvenile's tail has seven or eight narrower bars and no subterminal band. The short but full crest of this species can be conspicuous, while the face may suggest a ruff. The Papuan eagle has rather peculiar proportions, with a prominent head, powerful, large and black bill and cere, large eyes with brown to orange irises, a chesty build, extremely elongated, bare legs of a brownish-grey to dull orange colour, very long tail, and powerful feet with sharp claws. When seen sitting about the ground, it has an upright posture and an almost bustard-like appearance due to its unusual structure. Based on fragmentary data from captivity, both the eye colour and the leg colour may grow more vivid with age, with one record-aged male of 30 years old having red eyes. In flight, the upperside is homogeneously all grey-brown and the underwings are all cream like the underside, but for barred grey but dull flight feathers. Due to its unusual appearance it is unlikely to be mistaken for the other large, widespread New Guinea eagle, Gurney's eagle, a more typical aquiline-type eagle in appearance with significantly different proportions and form as well as clearly much darker dorsal colour (while juvenile Gurney's are far more pale and less bicolored). Additionally, Gurney's eagles dwells in forests as well but often tend to occur at slightly lower elevations than Papuan eagles and may be more prone to occurring near varying and less dense habitats. The wedge-tailed eagle and the white-bellied sea eagle are both very range-restricted in New Guinea and frequent drastically different habitats than the Papuan eagle. The more common long-tailed honey buzzard is much smaller than the Papuan eagle, with a different wing shape, a well-streaked underside and wing linings and broadly banded flight feathers and tail. Despite their distinctive appearance, the honey buzzard is not infrequently mistaken for a Papuan eagle in the dense, dark forests.

The call of the Papuan eagle is a startlingly loud uumpph or okh, suggesting a very loud hiccup or taut bowstring. Their call is said to carry quite well through the forest. The main call is occasionally followed by a somewhat chicken-like but more loud and powerful buk-buk-buk. Also, a deep resonant bungh-bungh may be uttered at 2-3 second intervals. A high-pitched whining call has also been reported. Pairs may call at dawn and dusk and even call during night. The greater coucal may at times produce a similar call, but has a more musical and descending-type call.

The Papuan eagle is the only member of the genus Harpyopsis. Despite its isolated range, the Papuan eagle was once thought to be related to the harpy eagle and the Philippine eagle based on similarities of morphology to these larger, but otherwise somewhat similar forest eagles. However, genetic studies showed that the Philippine eagle is actually derived from the lineage of the snake eagles, so is similar only through convergent evolution. The genetic data, however, showed that the Papuan eagle does appear to possess a highly similar genetic sequence to those of harpy and crested eagle, despite these neotropical species being particularly disparate in range from New Guinea (the crested eagle in particular is fairly similar in size and form to the Papuan, but is of more slender form with less extreme elongation of its legs and tail). Therefore, the Papuan eagle forms a clade with the harpy and crested eagles despite each species being distinct enough to retain their own monotypical genera.