National Geographic

New Zealand’s Long-Lost Giant Raptor

On Tuesday evening, just after I got back from the movies, I saw the infamous “Golden Eagle Snatches Kid” video. I wasn’t quite sure what to make of it.

The footage looked realistic enough. Far superior to Birdemic, at any rate. But there was something off about it, especially what seemed like the common trick of shooting something surprising at a distance, dropping the camera, and bringing the viewer back to the action with a close-up meant to hide the seams between fantasy and reality. Being that the movie I just went to see was The Hobbit – the climax of which features giant eagles that come to the rescue of the story’s imperiled heroes – I settled with making an unoriginal crack about the video and called it a night.

It didn’t take long for experts to debunk the film. The eagle didn’t appear to be any identifiable species, and, more importantly, there were various aspects of behavior and lighting that just didn’t make sense. Within a few hours, the digital animation students who created the video stepped forward and confirmed that the video was a gag, yet another bird-based fake brought to us by Montreal’s Centre NAD (home of the less-convincing “Penguin escaped zoo in Montreal!!!” hoax).

As Slate was quick to point out in the wake of the YouTube sensation, there aren’t any confirmed accounts of eagles or other raptors flying off with children. Old newspaper reports don’t amount to hard evidence. Yet that doesn’t mean that eagles would be incapable of flying off with relatively heavy loads – or, at least, parts of slain prey.

The famous “Taung child” – a young Australopithecus africanus, one of our early human relatives – was partly eaten by a raptor, and estimations of the victim’s and the predator’s body weight suggest that the bird was capable of at least carrying part of the youngster. Even though the child was too heavy to abscond with as a whole, a bird akin to the African crowned eagle would have been able to carry about thirteen pounds of weight – something the living birds have been observed to do.

Often, though, birds of prey kill their victims on the spot. Much like their ancient, feathery cousins among the deinonychosaurs – like the famous Deinonychus and Velociraptor – hawks, eagles, and their ilk have enlarged second toe claws that they use to pin prey following a strike. Eagles snatching people into the air is better left to Tolkein, or, at the very least, film students.

Still, the hoax, The Hobbit, and the blockbuster film’s connection to New Zealand reminded me of a huge eagle that once hunted moas on that very same island. Haast’s eagle, Harpagornis moorei, had an eight-foot wingspan and may have weighed as much as 33 pounds. To the best of my knowledge, no one has ever modeled whether these giant raptors would have been capable of picking up a child, and there is no direct evidence that the eagle attacked humans, but we do know that the bird was a skilled hunter of the large, flightless moas that strutted across New Zealand until about 600 years ago.

Humans undoubtedly observed Haast’s eagle in action. The Maori people, who arrived on the island sometime over 700 years ago, must have seen the raptor tearing at moas before the hungry humans themselves ultimately drove both the moa and the eagle into extinction. Today, ornithologists and paleontologists are only left with bones and the genetic material preserved within. Still, from those subfossil remains, researchers have slowly been piecing together the natural history of New Zealand’s lost mega-eagle.

The foot of Haast's eagle compared with a living relatve, the Little eagle. From Bunce et al., 2005.

The evolutionary relationships of Haast’s eagle are something of a paradox. Although significantly more massive than the largest living eagle, a 2005 study by Michael Bunce and colleagues found that the extinct Harpagornis moorei was actually most closely related to some of the smallest living eagles – raptors weighing about two pounds with wingspans of about four feet.

The huge size of Haast’s eagle, the researchers argued, was “an anomaly” within the bird’s lineage, perhaps driven by competition with other raptors, the size of the bird’s preferred prey, or the lack of terrestrial predators on ancient New Zealand. Similar conditions have been tied to the evolution of other large birds of prey on other islands, although never in a case so extreme as Haast’s eagle evolving from ancestors presumably about a tenth of its mass. Anatomy supports what the DNA evidence suggests. As described by Paul Scofield and Ken Ashwell in a 2009 study, the relatively small brain and eyes of Haast’s eagle indicates that it was a giant which rapidly evolved from a comparatively tiny ancestor.

Haast’s eagle represents a departure from the common evolutionary theme of isolated island birds becoming large, flightless ground dwellers. The raptor was a giant, no doubt about that, but it retained its ability to fly while various other members of New Zealand’s diverse avifauna became restricted to the earth. The multiple species of moa were the largest and now are the most famous of those birds, and, aside from the predator simply looking like an efficient moa-killer, we know that Haast’s eagle preyed upon its flightless cousins thanks to bonebeds and damaged skeletons.

Paleontologist Richard Holdaway examined the carnivorous habits of Haast’s eagle as part of his 1991 thesis. At the time, the idea that Haast’s eagle was a capable hunter was a controversial one. The bird was often thought to be an obligate scavenger, relying upon moas that had died from other causes. By the 1970s, though, ornithologists such as D.H. Brathwaite began to challenge this prevailing view, casting the raptor as a dedicated moa-killer.

After surveying the evidence, Holdaway presented two complementary arguments for why Haast’s eagle must have been a rapacious predator. For one thing, eagles were regularly preserved in natural traps – such a swamps and caves – that also contained moa bones. And a significant number of moa hips found at sites such as Glencrieff swamp bore punctures that could only have been made by the eagle.

The damaged bones only indicate that the eagles were feeding upon the moas, rather than showing us how the moas were killed. But the fact that eagle remains are consistently found in moa habitat, rather than all over the island, suggests that the raptors depended on their flightless prey. Haast’s eagle remains have been found in a variety of different habitats, with the constant being moas. While it’s true that the eagle may have also preyed upon smaller birds in the same environments, the co-occurrence of the raptor with the moas and the damaged moa bones indicates a close ecological connection.

Holdaway’s research undercut the scavenger hypothesis. If Haast’s eagle was a scavenger, it should have ranged over the whole island and taken advantage of any carrion it could find. Meat is meat. The fact that the eagle is consistently found in moa habitats indicate that Haast’s eagle was prey-limited – the raptor probably wasn’t above scavenging, but apparently relied on living populations of moa that lived in relatively open habitats at the edges of forests. The fact that the eagle went extinct when the moas were hunted into extinction supports this idea. And, as Scofield and Ken Ashwell argued, the brain of Haast’s eagle didn’t show brain expansions related to smell that would have assisted them in sniffing out rotting meat, as is seen among scavenging vultures. The constellation of evidence outlines a predator rather than a vulture-mimic.

So, in light of this week’s hoax and what we know about Haast’s eagle, did New Zealand’s raptor snatch up little moas and fly off with them to mountain roosts? Probably not. Even if Haast’s eagle was capable of such a feat, it didn’t have to. Haast’s eagle was New Zealand’s apex predator, a raptor that was beautifully-adapted to preying on other birds. Only with the arrival of moa-hunting humans did Haast’s eagle encounter competition on the ground, and, tragically, the sharp-clawed bird ultimately lost.

References:

Berger, L., Clarke, R. 1996. The load of the Taung child. Nature. 379: 778-779

Brathwaite, D. 1992. Notes on the weight, flying ability, habitat, and the prey of Haast’s eagle (Harpagornis moorei). Notornis. 39, 4: 239-247

Bunce, M., Szulkin, M., Lerner, H., Barnes, I., Shapiro, B., Cooper, A., Holdaway. 2005. Ancient DNA provides new insights into the evolutionary history of New Zealand’s extinct giant eagle. PLoS Biology. 3, 1: e9. doi: 10.1371/journal.pbio.0030009

Fowler, D., Freedman, E., Scannella, J., Kambic, R. 2011. The predatory ecology of Deinonychus and the origin of flapping in birds. PLoS ONE 6,12: e28964. doi:10.1371/journal.pone.0028964

Hedenstrom, A. 1995. Lifting the Taung child. Nature. 378: 670

Holdaway, R. 1991. Systematics and paleobiology of Haast’s eagle (Harpagornis moorei Haast, 1872) (Aves: Accipitridae). University of Canturbury thesis. 1-472

Scofield, R., Ashwell, K. 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. 9,3: 637-649. doi: 10.1671/039.029.0325

Worthy, T., Holdaway, R. 1996. Quaternary fossil faunas, overlapping taphonomies, and palaeofaunal reconstruction in North Canterbury, South Island, New Zealand. Journal of the Royal Society of New Zealand. 26, 3: 275-361. doi: 10.1080/03014223.1996.9517514

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