Mining for moa

No moa, no moa
In old Ao-tea-roa
Can’t get ’em
They’ve et ’em
They’re gone and there ain’t no moa’

New Zealand folk song.

At the time of Maori settlement in New Zealand, New Zealand’s bird fauna had been impacted by the arrival one thousand years earlier of rats, but those impacts had been focused on smaller species. Smaller rails, snipe, wrens and the like had been the casualties. Larger species may have been affected, but less so. The Laughing Owl possibly benefited from the rats, switching from a diet of native animals to the introduced rats.

The large avifauna of New Zealand was dominated by the moa. There were probably nine species of moa prior to the arrival of humans, ranging in size from the 20 kg male Stout-legged Moa to the 3 metre high 240 kg female North Island Giant Moa. I had to specify the sex in the above sizes because the moa were quite variable in size and weight. The Stout-legged Moa was highly variable, with the male ranging to as little as 9 kg (the size of a turkey) or as much as 34 kg. The female, on the other hand, could weigh as much as an ostrich (105 kg)! This massive variability led to many situations where scientists described the different sexes as different species.

In addition to the moa, New Zealand held numerous duck species. The two large geese species, related to Australia’s Cape Barren Goose, overlapped with the smaller moa in size and weight. Like many other new Zealand birds there was a North Island and a South Island species. This species pairing occurred with the adzebills as well. The adzebills were large birds related to the rail family named for their massive slightly curved bills. They are thought to have been omnivores, and like the New Zealand geese overlapped in size with the smaller moa (which is what they were thought to be when the first fossils were found).

These large birds were no more able to deal with new predatory species than the smaller birds were with the rats. The main predator of the moa and other large birds was the Haast’s Eagle. This massive predator had a wingspan of 2.6 metres and had claws the size of a tiger’s. It was likely able to take prey up to 20 times its own body mass, and would have even been able to take down humans straying into its hunting grounds. Needless to say tramping, or birdwatching, in the Southern Alps would have been a great deal more interesting with these guys around. The Haast’s Eagle was restricted to South Island, but another massive bird of prey, the Eyles’ Harrier, was found on both the main islands. This species is probably related to the Australasian Harrier that inhabits New Zealand today, but was four times heavier and had short wings adapted to a fast flapping flight. The species was probably able to tackle most New Zealand birds, even smaller moa.

A Haast’s Eagle attacks two moa. Artwork by John Megahan, released under a Creative Commons Attribution Generic 2.5 Licence

It was into this rich avian world that the Maori stepped 800 years ago. The initial settlers probably numbered no more than 200. But the archaeological evidence, backed up by some ecological modelling, shows that this small number was nothing less than a disaster for the large birds.

The moa were never particularly numerous to start with, there were probably never more than 110,000 birds (in all species) across the whole of New Zealand. The adzebills and geese were even less common. And like the smaller wrens and rails, the insular naivety of these large birds made them vulnerable to hunting. Hunting wasn’t particularly sophisticated, requiring nothing more than snares (Worthy and Holdaway note that large birds with long necks held forwards in dense bush seem pre-adapted for snaring), or simply approaching and clubbing the poor bird.

The speed at which this happened was remarkable. Both the model and the archaeological evidence show that within 100 years of settlement the moa was no longer or only rarely a part of the diet of the Maori. Across the whole of New Zealand. In some areas, particularly the damp multi-story forests of North Island, the period between the arrival of humans and the extinction of the moa would have been much shorter still. On the Coromandel Peninsula near Auckland it probably took ten, or as few as five, years for the moa to be consumed.

I’ve discussed earlier the reluctance of some early researchers to point the finger at hunting. Early models of hunting worked on the premise that there would have been a surplus of birds available for hunters to consume each year, to crop. But there wasn’t a surplus to crop. Moa were slow breeders with long maturation times, and as such they were vulnerable to adult mortality. In much the same way as albatrosses are suffering because of the increased death of adults due to long-lining, the massive increase in adult mortality caused by hunting were not offset by gains from reproduction. To quote Worthy and Holdaway again “[moa] were mined, not cropped”.

Doubtless some moa survived the first century of settlement, in remote parts of South Island’s Fiordlands perhaps, but even here hunting pressure would have been intense. Once the moa became rarer they became more desirable as prey – 19^th century observers recorded that hunters would trek great distances to hunt the increasingly rare Takahe when the common, and equally edible, Pukeko remained closer to their homes.

Moa were not the only bird to be hunted. The adzebills, larger ducks, New Zealand Raven and larger rails were also targeted, and all except the Takahe were extinct before the Europeans arrived. One species, the Auckland Island Merganser, survived only on the remote Auckland Islands (a group not successfully settled by anyone), but as with the Stephen’s Island Wren I discussed two weeks ago that distribution is an artefact. Other species that survived underwent range reductions. The King Shag became entirely extinct on North Island and survived only as a remanent in the northern tip of South Island.

The harrier, along with the massive Haast’s Eagle, would also have suffered as they prey supplies were impacted by hunting, although it has been suggested that the Haast’s Eagle would have suffered addition persecution, as a species (the only native species) capable of hunting the humans back.

A great deal was lost before the Europeans arrived, and is known only from fossils. But the story was by no mean over yet. European settlement was to make even more massive changes to the avifauna, and the overall ecology, of New Zealand, and it is that story I shall tell next week.