Haast's Eagle: Hieraaetus moorei

[Infinity Blade]

Haast's Eagle-Hieraaetus moorei


Depiction of Haast’s eagle preying upon a moa. © @ Julio Lacerda->

Temporal range: Pleistocene (diverged from little eagle 2.22 Ma[1]; oldest fossil remains date to 130-75 kyr BP[2]) to Holocene (Meghalayan); extinct by mid-15th century CE[3]

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Reptilia or Sauropsida
Clade: Eureptilia
Clade: Romeriida
Clade: Diapsida
Clade: Neodiapsida
Clade: Archelosauria
Clade: Archosauromorpha
Clade: Archosauriformes
Clade: Crurotarsi
Clade: Archosauria
Clade: Avemetatarsalia
Clade: Ornithodira
Clade: Dinosauromorpha
Clade: Dinosauriformes
Clade: Dinosauria
Order: Saurischia
Clade: Eusaurischia
Clade: Theropoda
Clade: Neotheropoda
Clade: Averostra
Clade: Tetanurae
Clade: Orionides
Clade: Avetheropoda
Clade: Coelurosauria
Clade: Tyrannoraptora
Clade: Maniraptoriformes
Clade: Maniraptora
Clade: Pennaraptora
Clade: Paraves
Clade: Eumaniraptora
Clade: Averaptora
Clade: Avialae
Clade: Euavialae
Clade: Avebrevicauda
Clade: Pygostylia
Clade: Ornithothoraces
Clade: Euornithes
Clade: Orithuromorpha
Clade: Ornithurae
Clade: Neornithes
Infraclass: Neognathae
Clade: Inopinaves
Clade: Telluraves
Clade: Afroaves
Clade: Accipitrimorphae
Order: Accipitriformes
Family: Accipitridae
Subfamily: Aquilinae
Genus: †Hieraaetus
Species: †H. moorei

Haast’s eagle is an extinct species of eagle endemic to New Zealand from the Pleistocene epoch[1][2] to the mid-15th century CE.[3]

Taxonomy:
Although Haast’s eagle was originally thought to be within its own genus, Harpagornis, analysis of ancient DNA has demonstrated it to be most closely related to eagle species within the genus Hieraaetus, including the extant little eagle (H. morphnoides) and booted eagle (H. pennatus). This led to the species being reclassified as a Hieraaetus moorei.[4] Of the two aforementioned extant Hieraaetus species, Haast’s eagle is most closely related to the little eagle.[1]

Evolution:
Haast’s eagle separated from the little eagle 2.2 million years ago. Interestingly, Haast’s eagle is estimated to have been 15 times heavier than its living Australian relative. Because it is phylogenetically nested within a clade of mostly small eagles (barring itself), it can be assumed that the last common ancestor between the two species was small itself.[1]

Description and biology:
Mass estimates for female Haast’s eagle go up to 14-15 kg, with wingspan estimates of 2.43 to 3 meters.[5][1] Males were smaller and are estimated to have weighed 11.5 kg at a wingspan of 2.14 meters.[5] To put this into perspective, the largest extant eagle, the harpy eagle (Harpia harpyja) weighs ~9 kg.[5] This makes Haast’s eagle the largest eagle to have ever lived.[1]

The rapid increase in size from a small to giant eagle is thought to be unique within vertebrate lineages.[4] It evolved so rapidly in size that the size of the brain lagged behind. Accordingly, the expansion of some somatosensory systems (particularly vision, olfaction, and vestibular function) was either minimized or highly restricted. Central visual processing was likely proportionally poor, although there was probably no functional advantage to enlarging the vestibular apparatus beyond that attained at 4-5 kg. Due to the probable lack of enough motor and proprioceptive control to swerve between dense vegetation (the short wings notwithstanding), Haast’s eagle probably hunted in open areas. Most remains of Haast’s eagle appear to come from open terrain.[6]

However, the synsacral nerves of Haast’s eagle suggests that the hindlimb muscles and joints were highly innervated with motor and/or proprioceptive fibers, giving it fine control in its legs. This gave the hindlimb the power and sensitivity to grapple with large prey such as moa. The lack of a significantly adapted visual, vestibular, and olfactory apparatus (due to such a rapid increase in size), coupled with the well developed motor control in the legs, argue strongly against past proposals of the bird being a vulture-like scavenger. Instead they suggest that Haast’s eagle evolved extremely rapidly to become an active hunter of large prey like the moa.[6]

This eagle has been described as having possessed a long, “vulture-like” beak, with damage on moa bones indicating that the bill could reach the internal organs of the ratites.[7][5] The beak was not out of proportion relative to body mass, but due to its large size could have exerted a powerful pull.[8]

The largest known claw cores were in excess of 60 mm long, with the keratin sheath adding another 30 mm (50% longer than the bone core). Thus, in life, the talons of Haast’s eagle were as long as the claws of an adult tiger.[5][7] The same claim (or a variation thereof) is also often made of the modern harpy eagle’s talons. Haast’s eagle’s talons were proportionately shorter than the harpy eagle’s, which simply has long talons for its size. Instead, the talons were thicker and more robust, with deeper flexor tubercles. This meant that Haast’s eagle could exert more force to the ends of its thicker claws. By contrast, vultures lack deep flexor tubercles and have very limited use for their feet, while harpy eagles have flexor tubercles more in proportion to their size and prey on mammals up to their own body mass. Coupled with the relatively thicker tibiotarsus and tarsometatarsus, Haast’s eagle was well equipped to pierce moa flesh and bones with its talons.[8]

Puncture marks on moa pelves made by the talons of H. moorei are well known. In Canterbury, over a dozen moa pelves have been recovered with talon marks made by this eagle.[9] Haast’s eagle is thought to have been capable of preying upon even adult giant moa (Dinornis robustus), which can weigh up to 200 kg.[9][10] Moas, geese (Cnemiornis), and adzebills were all likely prey items, although adzebills were possibly rare.[10] Also possibly in this eagle’s diet were coot, Finsch’s duck, kakapo, and takahe[9], but any birds smaller than the last two would have been too small for the eagle to grasp with its huge talons.[10]

Analysis of the bones of Haast’s eagle suggests body, especially wing, proportions similar to those of forest eagles. Authors have previously suggested that the species was becoming flightless or was a poor flier due to its massive size and/or relatively short wings. The sternum’s robust and fully developed keel, expanded neural canal in the thoracic vertebrae at the shoulder, and normal body proportions for an eagle of this size, are all evidence against this assertion. Haast’s eagle was indeed a competent flier, with morphological comparisons to other species suggesting it was better adapted for flapping than soaring flight.[8]

Extinction:
Haast’s eagle was the apex predator of New Zealand before the arrival of Polynesian settlers in the late 13th century CE. The Māori managed to hunt all species of moa by the mid 15th century.[2] The loss of its prey base and anthropogenic environmental change forced Haast’s eagle into extinction along with the moa. Haast’s eagle bones have also been found in Polynesian middens.[5] This might suggest some predation by humans as well.

References:

[1] Knapp, M., Thomas, J. E., Haile, J., Prost, S., Ho, S. Y., Dussex, N., ... & Gilbert, M. T. P. (2019). Mitogenomic evidence of close relationships between New Zealand’s extinct giant raptors and small-sized Australian sister-taxa. Molecular phylogenetics and evolution, 134, 122-128.
[2] Perry, G. L., Wheeler, A. B., Wood, J. R., & Wilmshurst, J. M. (2014). A high-precision chronology for the rapid extinction of New Zealand moa (Aves, Dinornithiformes). Quaternary Science Reviews, 105, 126-135.
[3] Worthy, T. H., & Grant‐Mackie, J. A. (2003). Late‐Pleistocene avifaunas from Cape Wanbrow, Otago, South Island, New Zealand. Journal of the Royal Society of New Zealand, 33(1), 427-485.
[4] Bunce, M., Szulkin, M., Lerner, H. R., Barnes, I., Shapiro, B., Cooper, A., & Holdaway, R. N. (2005). Ancient DNA provides new insights into the evolutionary history of New Zealand's extinct giant eagle. PLoS Biol, 3(1), e9.
[5] Hume, J. P. (2017). Extinct Birds. United Kingdom: Bloomsbury Publishing.
[6] Scofield, R. P., & Ashwell, K. W. (2009). Rapid somatic expansion causes the brain to lag behind: the case of the brain and behavior of New Zealand's Haast's Eagle (Harpagornis moorei). Journal of Vertebrate Paleontology, 29(3), 637-649.
[7] Reilly, J. (2018). The Ascent of Birds: How Modern Science is Revealing Their Story. Pelagic Publishing Ltd.
[8] Worthy, T. H., & Holdaway, R. N. (2002). The lost world of the moa: prehistoric life of New Zealand. Indiana University Press.
[9] Holdaway, R. N., & Worthy, T. H. (2008). Late Quaternary avifauna. The Natural History of Canterbury, 65-88.
[10] Brathwaite, D. H. (1992). Notes on the weight, flying ability, habitat, and prey of Haast’s Eagle (Harpagornis moorei). Notornis, 39(4), 239-247.

[Infinity Blade]

New Zealand's extinct giant raptor (Hieraaetus moorei) killed like an eagle, ate like a condor


© @ Katrina Kenny

The extinct Haast's eagle or harpagornis (Hieraaetus moorei) is the largest known eagle. Historically, it was first considered a predator, then a scavenger, but most recent authors have favoured an active hunting ecology. However, the veracity of proposed similarities to carrion feeders has not been thoroughly tested. To infer feeding capability and behaviour in harpagornis, we used geometric morphometric and finite-element analyses to assess the shape and biomechanical strength of its neurocranium, beak and talons in comparison to five extant scavenging and predatory birds. The neurocranium of harpagornis is vulture-like in shape whereas its beak is eagle-like. The mechanical performance of harpagornis is closer to extant eagles under biting loads but is closest to the Andean condor (Vultur gryphus) under extrinsic loads simulating prey capture and killing. The talons, however, are eagle-like and even for a bird of its size, able to withstand extremely high loads. Results are consistent with the proposition that, unlike living eagles, harpagornis habitually killed prey larger than itself, then applied feeding methods typical of vultures to feed on the large carcasses. Decoupling of the relationship between neurocranium and beak shape may have been linked to rapid evolution.

Results of our combined analyses reveal a novel mosaic of morphological and biomechanical features attributable to the cranium of Hie. moorei. Regarding shape, its beak is eagle-like but its neurocranium is closest to that of the two carrion feeders, Vul. gryphus in particular. This contradicts interpretations based on two-dimensional analyses that the closest similarities between Hie. moorei and vultures were evident in the beak.

Hieraaetus moorei was also characterized by a combination of eagle-like and vulture-like features with respect to the mechanical performance of the cranium. Under the intrinsic load, mean strain in Hie. moorei was considerably lower than in any other taxon, but closest to that of eagles. This suggests a capacity to withstand loads generated by a particularly powerful bite for its size. High mean strains recorded in Vul. gryphus, Hal. sphenurus and Hie. moorei for dorsoventral pulling suggest that these species are not well adapted for this behaviour. Similarly, high mean strain for Hie. moorei under the lateral shaking simulation indicates that this species was poorly adapted to perform this behaviour relative to extant eagles and again was closest to the carrion feeding Vul. gryphus. Interestingly, the other carrion feeder, the Aeg. monachus, records very low strain for the lateral shake. Under the pullback loading, Hie. moorei and the two scavengers all perform better than the remaining taxa and the giant eagle was again closest to Vul. gryphus, which is consistent with feeding observations and functional anatomy of vultures.

How then to interpret this unique combination of characters in Hie. moorei? Talons are the primary killing tools of most raptors, except falcons; however, their beak may be used to finish a kill. We propose that biting may have been more important in delivering the kill for Hie. moorei than is typical among extant eagles. With respect to the extrinsic FEA, we first note that there is a clear difference between the two known carrion feeders included in the analyses. Aegypius monachus was able to withstand high lateral loadings, whereas both Hie. moorei and Vul. gryphus performed poorly in this regard. This is consistent with the classification of Aeg. monachus as a ripper of flesh that favours the tough skin and meat of large mammal carcasses, possibly with strong lateral forces as well as powerful biting. Aegypius monachus is a large and aggressive vulture that dominates other avian scavengers when fights occur over a carcass. By contrast, Vul. gryphus is a ‘gulper’ that focuses on the softer internal organs. Our findings of more vulture-like features in the extrinsic FEAs, therefore, are most consistent with the proposition that Hie. moorei may have preferentially targeted the high nutrient viscera of its prey that are also favoured by most carrion-feeding raptors.

This mix of morphologies and mechanical behaviours reminiscent of obligate carrion feeders, as well as predacious eagles, may be the result of a unique combination of selective pressures. Vultures generally feed on animals much larger than themselves, but eagles typically kill and eat relatively small prey. Taphonomic evidence leaves little doubt that Hie. moorei killed and fed on moa, including the largest, Dinornis, which could weigh over 200 kg. Even the smallest of moa species (little bush moa, Anomalopteryx didiformis; approximately 30 kg) was larger than Hie. moorei. Hieraaetus moorei probably inhabited open plains, as did many of its prey species. Its vision was evidently not particularly acute, but without competition, this was probably not under strong selection. Hieraaetus moorei used a flapping flight, suggesting flight occurred over relatively short distances. Together the evidence suggests that Hie. moorei could have swooped down from trees or cliffs at short distances to catch and kill its prey. Our results are largely consistent with the proposition that Hie. moorei habitually killed particularly large prey in a typically eagle-like fashion using its powerful talons, but then applied feeding techniques common to vultures that eat from the carcasses of species much larger than themselves. Bird skin is typically less tough than that of mammals, so Hie. moorei was able to open the carcasses itself. It is notable that Hie. moorei is less well adapted to eating hard tissues, such as tendons, than Aegypius, but probably preferred viscera and muscles, like Vultur.

Our proposal that Hie. moorei favoured the internal organs of its prey leads to the possibility that, as well as vulture-like nostril scrolls and vulture-like feeding mechanics, like most vultures, its head and neck were featherless. This proposition is also consistent with a Maori rock art depiction of what is thought to be a Hie. moorei, in the Cave of the Eagle at Craigmore Station, South Island (figure 5). The raptorial bird has a dark-coloured body, but the head and neck remain uncoloured.

royalsocietypublishing.org/doi/10.1098/rspb.2021.1913

[Infinity Blade]

I ordered a life size reproduction of this eagle's foot online and got it in the mail today. This thing's foot span was as wide as my forearm is long and could literally grab me by the head or the waist.

[Exalt]

I discussed this once on twitter, possibly with Infinity Blade, but percentage-wise, Haast's Eagle is one of the predators most outweighed by it's prey. Despite this, I have never seen anyone suggest that the eagles may have co-operated. Birds doing this is rare, but not completely unheard of. Is it simply the rarity of this, combined with behavior generally not fossilizing, and the sheer power of those claws? I have seen at least two people compare Haast's feet to that of a tiger, which is pretty crazy considering a tiger is obviously much larger.

[Supercommunist]

Harris hawks hunt in packs, but generally raptors only work together in pairs. I assume that's because pack hunting is not really necessary. Eagles are already capable of killing much larger prey like pronghorns by themselves.

[Exalt]

I see. I hadn't heard of this outside of golden eagles using gravity to kill goats.

[Supercommunist]

IB actually had a really cool post about deinoychus that touches upon a eagles ability to kill pronghorns. Basically, there is nothing really stopping them from riding an ungulates back and eating it alive. I think in most cases birds of prey don't hunt in packs because it's just not needed.