This Extinct Eagle May Have Gulped Guts Like a Vulture
Scientists suggest the largest eagle that ever existed hunted down its 500-pound prey and then stuck its head inside to gorge on organs.,
At Craigmore Station in Canterbury, New Zealand, an ancient Maori painting decorates the limestone overhang of a cave. Thought to depict an extinct eagle, the painted raptor gives the cave its name: Te Ana Pouakai, or the Cave of the Eagle. But this wasn’t just any bird — it may have been a Haast’s eagle, which had wingspans between six and 10 feet, making the species the largest known eagle.
The Maori artist painted the bird with a dark body and an outline of a head and neck that is more reminiscent of the bald head of a vulture than the feathery dome of an eagle.
Now, a group of scientists suggest the extinct eagle may have looked just like its painted form. By creating 3-D models of the extinct bird’s skull, beak and talons, the group tested how well the eagle performed against living raptors in a series of feeding simulations. Their results, published Wednesday in the journal Proceedings of the Royal Society B, argue the Haast’s eagle hunted like a predatory eagle but feasted like a scavenging vulture.
“It’s a unique, chimera-like combination for a bird,” said Stephen Wroe, a researcher from the University of New England in Armidale, Australia, and an author on the paper.
Though the eagles were first described in the late 19th century, the question of whether the creature was a hunter or carrion feeder went unresolved for decades. Recent analyses of the eagle’s nervous system and sensitive, powerful talons have made a strong case that the large bird killed prey like modern eagles.
“Modern eagles eat things that are smaller than themselves, so they can eat it in two or three bites,” said Anneke van Heteren, a researcher at the Bavarian State Collection of Zoology in Munich and an author on the paper.
But many scientists have pointed to the Haast’s eagle’s more vulture-like characteristics, such as bony structures around the nostrils, which help scavengers feed inside a much larger animal without accidentally suffocating themselves.
“When they get their head into the goo, they don’t want to get that in their nose,” Dr. van Heteren said. Dr. Wroe had received CT scans of a Haast’s eagle skull around a decade ago. But study of the animals potentially vulture-like features remained on the back burner for years until Dr. van Heteren took it on.
The researchers used a technique called geometric morphometrics, identifying landmarks on the bone, to capture the shape of the Haast’s eagle’s skull, beak and talons in three dimensions.
Just as eagles can specialize in hunting specific prey, vultures do not all scavenge in the same way. Some, known as “rippers,” feed on the tough skin of a carcass. “Gulpers” slurp up the soft, nutrient-rich innards. And “scrappers” eat small scraps.
The authors compared their model of the Haast’s eagle to models of living vultures and eagles, which exhibited a range of feeding styles from hunting to scavenging. They examined the cinereous vulture, a “ripper,” and the Andean condor, a “gulper,” as well as several eagles that hunted prey of various sizes. The researchers ran the models through simulations of feeding behavior.
“Vultures feed on animals that are a lot bigger than themselves,” Dr. Wroe said. “They have to thrust their head deep into the abdominal cavity of a rotting zebra carcass and pull out the high nutrient value, soft internal organs: heart, lungs, liver.”
The Haast’s eagle model performed like a vulture in certain tests and like an eagle in others. It had the talons of an eagle and was excellent at biting down on prey. But it was not as good at ripping off chunks of meat. It fed like a vulture, closely matching the gulping Andean condor in its ability to nose inside a carcass.
The researchers say these results suggest the Haast’s eagle killed moa and then ate their guts. “It’s no mean feat, because it was a heck of a big bird,” Dr. Wroe said of moas, which could weigh up to 550 pounds.
Guillermo Navalon, a postdoctoral researcher at the University of Cambridge who was not involved with the study, said he found the authors presented strong evidence for Haast’s eagle’s hunting prowess.
But he said that the similarity in skull shape between the Haast’s eagle and vultures could be a result of their similarly large sizes rather than an indication of feeding behavior, and pointed to a 2016 study that found larger raptors have different cranial shapes than smaller raptors. Dr. Navalon suggested a more comprehensive analysis of the skull shapes could have clarified whether the similarities were related to scavenging, instead of just the birds’ large size.
When the paper was nearly finished, one of the authors wondered if the Haast’s eagle was bald like many modern vultures. Dr. van Heteren thought of the scientific accuracy of European cave art, and the researchers scoured the internet for drawings of Haast’s eagle in New Zealand caves.
In their searching, they stumbled upon a photo of the painted overhang of the Cave of the Eagle, depicting the dark-colored bird with the uncolored head — evidence, perhaps, of baldness.
“When you look at it, I don’t know what else it could be,” Dr. van Heteren said. “These people were eyewitnesses, why not take their word for it?”