Haast's eagle (Hieraaetus moorei), sometimes known as Fuller's eagle, is an extinct species of eagle that lived in the South Island of New Zealand, commonly accepted to be the pouākai of Māori mythology. It is the largest eagle known to have existed, with an estimated weight of 10–18 kilograms (22–40 pounds), compared to the next-largest and extant harpy eagle (Harpia harpyja), at up to 9 kg (20 lb). Its massive size is explained as an evolutionary response to the size of its primary prey—the flightless moa—the largest of which could weigh 200 kg (440 lb). Haast's eagle became extinct around 1445, following the arrival of the Māori, who hunted moa to extinction, introduced the Polynesian rat (Rattus exulans), and destroyed large tracts of forest by fire.
Taxonomy Haast's eagle was first scientifically described by Julius von Haast in 1871 from remains discovered by the Canterbury Museum taxidermist, Frederick Richardson Fuller, in a former marsh.
Etymology Haast named the eagle Harpagornis moorei after George Henry Moore, the owner of the Glenmark Estate, where the bones of the bird were found. The genus name was from the Greek harpax, meaning "grappling hook", and ornis, meaning "bird". In an article in 2025, the biologist Richard Holdaway said he had coined the now-conventional common name Haast's eagle in the early 1990s but on later reflection proposes a more suitable name be Fuller's eagle, after its actual discoverer.
Evolution DNA analysis later showed that this bird is related most closely to the much smaller little eagle (Hieraaetus morphnoides) as well as the booted eagle (Hieraaetus pennatus) and not, as previously thought, to the large wedge-tailed eagle (Aquila audax). Harpagornis moorei was therefore reclassified as Hieraaetus moorei. H. moorei is estimated to have diverged from these smaller eagles as recently as 1.8 million to 700,000 years ago. If this estimate is correct, its increase in weight by 10 to 15 times is an exceptionally rapid weight increase. The suggested increase in the average weight of Haast's eagle over that period would therefore represent the largest, fastest evolutionary increase in average weight of any known vertebrate species. This was made possible in part by the presence of large prey and the absence of competition from other large predators, an example of ecological release and island gigantism. A recent mitochondrial DNA study found it to be more closely related to the little eagle than the booted eagle, with an estimated divergence from the little eagle around 2.2 million years ago. It was placed in the genus Aquila by recent taxonomists.
Description
Haast's eagle was one of the largest known true raptors. In length and weight, it was even larger than the largest living vulture (the Andean condor). Another giant bird (not actually an eagle save for in name) more recently and scantily described from the fossil record, Woodward's eagle, which resided in North America, rivaled Haast's eagle in at least the aspect of total length. Female eagles were larger than males. Most estimates place the female Haast's eagles in the range of 10–18 kg (22–40 lb) and males around 9–12 kg (20–26 lb). A comparison with living eagles of the Australasian region resulted in estimated masses in Haast's eagles of 11.5 kg (25 lb) for males and 14 kg (31 lb) for females. One source estimates that the largest females could have weighed more than 16.5 kg (36 lb). The largest extant eagles, none of which are verified to exceed 9 kg (20 lb) in a wild state, are about forty percent smaller in body size than Haast's eagles.
It had a relatively short wingspan for its size. It is estimated that the grown female typically spanned up to 2.6 m (8 ft 6 in), possibly up to 3 m (10 ft) in a few cases. This wingspan is broadly similar to the larger range of female size in some extant eagles: the wedge-tailed eagle (A. audax), golden eagle (A. chrysaetos), martial eagle (Polemaetus bellicosus), white-tailed eagle (Haliaeetus albicilla) and Steller's sea eagle (Haliaeetus pelagicus) are all known to exceed 2.5 m (8 ft 2 in) in wingspan. Several of the largest extant Old World vultures, if not in mean mass or other linear measurements, probably exceed Haast's eagle in average wingspan as well. Haast's eagle's relatively short wingspan has sometimes led to it being incorrectly portrayed as having evolved toward flightlessness, even though evidence strongly suggests that it flew. Instead, its short and broad wings represents an evolutionary departure from the mode of its ancestors' soaring flight in favour of navigating through a crowded woodland environment. Haast's eagles are likely to have hunted within the dense shrubland and forests of New Zealand, somewhat akin to other forest-dwelling raptors like the goshawks or harpy eagle. Some wing and leg remains of Haast's eagles permit direct comparison with living eagles. The harpy eagle, the Philippine eagle (Pithecophaga jefferyi), and the Steller's sea eagle are the largest and most powerful living eagles, and the first two also have a similarly reduced relative wing-length as an adaptation to forest-dwelling. A lower mandible from Haast's eagle measured 11.4 cm (4+1⁄2 in) and the tarsus in several Haast's eagle fossils has been measured from 13.7 to 16.2 cm (5+3⁄8 to 6+3⁄8 in). In comparison, the largest beaks of eagles today (from the Philippine and the Steller's sea eagle) reach a little more than 7 cm (3 in); and the longest tarsal measurements (from the Philippine and the Papuan eagle, Harpyopsis novaeguineae) top out around 14 cm (5+1⁄2 in).
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