In a land without lions, wolves, or even snakes, the apex predator of this realm once had feathers.
Before the first Polynesian settlers stepped onto New Zealand’s shores some 750 years ago, the island nation was home to one of the most formidable birds to have ever flown — birds like Haast’s eagle (Hieraaetus moorei), a raptor so massive and deadly it earned the nickname “the flying tiger.”
Weighing up to 40 pounds (18 kg), with a wingspan stretching nearly 10 feet (3 meters), it was the largest eagle known to science. And it feasted on giants.
Its prey included the moa — a group of flightless birds that stood taller than a basketball player and weighed as much as 440 pounds (200 kg). Though the eagle was a fraction of the moa’s size, it regularly brought them down in brutal ambushes, digging three-inch talons into their hindquarters and finishing the kill with a lethal blow from its hooked beak. According to researchers, it then reached into the open carcass seeking the internal organs.
Haast’s eagle may have attacked moa like an eagle, but it would have fed on them like a vulture.
A Lost World in the South Pacific
New Zealand’s wildlife evolved in splendid isolation. Before humans arrived, the islands were a mammalian void — no bears, no foxes, no big cats. Instead, the archipelago was ruled by birds. There were more than 200 native avian species, many of them flightless. With no land predators to fear, birds filled every niche, from insect-chasers to megafaunal herbivores.
Haast’s eagle was one of the few predators on the islands. Its bones were first unearthed in the 1860s by farm workers draining a swamp. Named after the 19th-century explorer Julius Haast, the raptor quickly captured the public’s imagination. Yet for decades, researchers puzzled over its strange proportions: legs like a tiger, but a head resembling a vulture. Some wondered if it could fly at all.
Recent studies have put those doubts to rest. The bird could indeed fly — and it flew with purpose. Scientists now know it combined the killing power of an eagle with the feeding habits of a scavenger. “It’s always been a puzzle with Haast’s eagle,” said Dr. Joanne Cooper, a senior curator at the Natural History Museum in London. “The head end looks quite vulture-like, while the feet end looks very eagle-like.”
This unusual anatomy was likely an adaptation to its unique ecological challenge: taking down prey far larger than itself and feeding on them on the spot, since it couldn’t possibly carry them away.
The Fastest Growth in the Animal Kingdom?
If Haast’s eagle’s size is staggering, how fast it got there is even more remarkable.
A genetic study published in PLOS Biology in 2005 revealed the eagle’s closest living relatives are among Australia’s tiniest raptors — the booted eagle and the little eagle, each weighing just over 2 pounds. The Haast’s eagle, by contrast, was fifteen times heavier. And yet, DNA shows the birds diverged just 2.2 million years ago.
Rapid changes in size have been observed in dogs, but that’s a process driven by human selection.
“That’s a staggering rate of change,” said Michael Knapp, an evolutionary biologist at the University of Otago. “I know of no other instance where natural selection led to such substantial growth over such a short period.”
Scientists call this phenomenon island gigantism — when smaller species, isolated on islands, grow far larger to fill ecological gaps. Usually, it happens gradually. But the Haast’s eagle’s transformation was lightning fast, driven by the opportunity to prey on moa, which had no natural enemies.
“There was huge amounts of meat that wasn’t taken,” Knapp told Knowable Magazine. “That scenario would have quickly selected for the largest eagles.”
To pinpoint how this biological growth spurt occurred, Knapp and his team are now hunting for the specific genes responsible by comparing the genomes of various species of eagle. “Finding out how that works on the molecular level, that’s really the next step,” he said.
The Bird That Came to Dinner
The idea that New Zealand’s birds evolved in place from ancient Gondwanan ancestors was once widely accepted. The country’s nickname, Moa’s Ark, reinforces the view of a biological time capsule adrift in the South Pacific. But geological evidence has since upended that story.
About 25 million years ago, during the Oligocene period, much of New Zealand may have been underwater. Only small scraps of land likely remained above the waves. This suggests many native species — including Haast’s eagle — didn’t evolve in place but arrived later, flying across the Tasman Sea from Australia.
The arrival of Haast’s eagle, researchers believe, coincided with a time of great environmental upheaval. Around 2.5 million years ago, the ice ages began. Forests receded, and grasslands emerged. These open habitats provided perfect hunting grounds. Not just for the eagle, but for a whole wave of avian immigrants. Knapp refers to these as “natural invasions,” events driven by ecological opportunity rather than human interference.
Curiously, Haast’s eagle wasn’t the only raptor to undergo rapid gigantism in New Zealand. Another species, Eyles’s harrier (Circus eylesi), also grew several times larger than its closest relatives. Genetic studies show it, too, arrived around the same time and underwent an evolutionary growth spurt.
These birds tell a story not just about evolution but about how habitat changes open the door to newcomers.
When the Moa Fell, So Did Haast’s Eagle
Haast’s eagle reigned for hundreds of thousands of years. But like so many island giants, it was vulnerable.
Polynesian settlers — ancestors of the Māori — reached New Zealand around the year 1250. Within two centuries, the moa were gone. Overhunted and displaced by fire-cleared forests, they vanished from the landscape. Their extinction marked the end for Haast’s eagle, which relied almost entirely on moa for food.
While direct evidence of human-eagle conflict is sparse, Māori oral tradition remembers the giant raptor. Stories describe the pouākai, a great bird said to have snatched away children. Some cave paintings appear to depict the eagle with a featherless head — another vulture-like adaptation that helped it feed on carrion.
Most likely, these settlers’ interventions brought the eagle and humans into direct conflict.
“It’s hard to imagine a bird in that role,” said Cooper. “But if it could successfully hunt a 250-kilogram moa, then 80-kilogram humans were possibly on the menu.”
The eagle’s extinction was swift. With no food and no forests, it had no real future. By the time European colonists arrived, Haast’s eagle was long gone. Some accounts suggest a pair survived into the 1800s, but no firm evidence remains.
Its loss left a unique void in global biodiversity. “There’s nothing really like it in the world anymore,” Cooper said.
