by Dr Paul Scofield
Swooping on 3 metre wings through the forests of pre-human New Zealand, Haast's Eagle was our apex predator. The world's largest eagle and the only animal capable of hunting the larger species of moa, it could weigh up to 15 kg.
Haast's Eagle preyed on moa. John Megahan, CC BY 2.5
The world has been fascinated by this enormous bird of prey since the Museum's founder, Julius Haast, first described it in 1871. Drawings on the walls of some South Island rock shelters suggest it fascinated Māori long before that. But we've only recently understood how it came to be here.
I contributed to a study, published in the journal Molecular Phylogenetics and Evolution, that suggests Haast's Eagle evolved relatively recently from a much smaller Australian ancestor.
We compared DNA extracted from a Haast's Eagle shoulder bone in the Museum's collection to the DNA of its closest living relatives, Australia’s Little Eagle and the Eurasian Booted Eagle. These birds have wingspans of just over a metre and typically weigh around 1 kg, which means they would have been dwarfed by their extinct Kiwi cousin.
The common ancestor of the Little Eagle and Haast’s Eagle probably arrived in New Zealand from Australia near the start of the most recent Ice Age – less than 2.5 million years ago.
At the time advancing glaciers were clearing swathes of New Zealand’s dense forest, likely providing suitable open habitat for the ancestor eagle to establish itself. New Zealand’s fauna included large avian herbivores like moa, but lacked an apex predator to prey on them. Haast’s Eagle grew to fill this niche, which on other landmasses is occupied by mammals like lions and wolves.
Our study also analysed DNA from another giant New Zealand native raptor, Eyles’ Harrier, a hawk species more than three times larger than the Swamp Harriers common in New Zealand today. The DNA showed that like Haast’s Eagle, Eyles’ Harrier‘s closest genetic relative was a much smaller Australian species, the Spotted Harrier. The two species likely diverged around the same time Haast’s Eagle split from its smaller cousins.
Chart showing the evolution of Eyles' Harrer and Haast's Eagle
These giant birds of prey went through some really dramatic changes in a relatively short time. Two and a half million years is not long in evolutionary terms. It’s a much shorter time frame than was originally thought.
These results fit into a broader trend in our field, where we’re increasingly finding that species we see as iconic New Zealand species are actually quite recent arrivals.
Haast's Eagle and Eyles' Harrier are examples of what scientists call “island gigantism” – a biological phenomenon where the size of an animal species isolated on an island increases dramatically in comparison to its relatives elsewhere. Other New Zealand species showing island gigantism include Takahe, Kakapō and the now-extinct Moa, Adzebill and New Zealand’s native geese.
Many of New Zealand's island giants, including Haast's Eagle and Eyles' Harrier, went extinct soon after the arrival in New Zealand of a new apex predator: humans. The birds probably just couldn't compete with humans when it came to hunting the other large birds that were their preferred prey.
Michael Knapp, Jessica E. Thomas, James Haile, Stefan Prost, Simon Y.W. Ho, Nicolas Dussex, Sophia Cameron-Christie, Olga Kardailsky, Ross Barnett, Michael Bunce, M. Thomas P. Gilbert, R. Paul Scofield. 2019. Mitogenomic evidence of close relationships between New Zealand’s extinct giant raptors and small-sized Australian sister-taxa. Molecular Phylogenetics and Evolution.
Dr Paul Scofield is Senior Curator Natural History