Imagine a world without mammals, a primeval world of cool, wet forests filled with mosses, ferns and lichens and inhabited by flightless birds. This was the world of the Moa, in New Zealand before the coming of human beings. For millions of years, New Zealand was isolated from the rest of the world. Only three species of bats and some sea lions made it to those shores. Instead, the islands were inhabited by members of the bird order Struthiformes which radiated out to become the dominant herbivores of the New Zealand forests, the Moas.
There have been ten species of Moas identified from fossils. The largest species, Dinornis robustus and Dinornis novaezelandiae, grew to 1.6 meters high and weighed up to 250 kg, but the rest were about the size of turkeys and, together with the kiwis and the flightless rails, dominated the island ecosystems. All were herbivores, feeding on the foliage, flowers and fruits of trees and shrubs. They were hunted by Haast's Eagle, the largest eagle that ever lived. The female eagles weighed in at a wopping 10-15 kg, twice the weight of an average Wedge-tailed Eagle in Australia today. These eagles had shorter wings than other eagles, probably as an adaptation for hunting in forests, but they were much heavier, presumably to help them bring down moas, their primary food source.
What we know about Moas comes from studies of fossils and studies of their closest living relatives, the kiwis. Moas are shown in pictures as carrying their heads upright, making them look very impressive. But kiwis carry their heads horizontally and pointing forward and it is likely that moas did the same. As in kiwis, the females were larger than the males, so much so that they were originally described as separate species. Kiwi females lay huge eggs and then the males incubate them. It is likely that moas did the same. From growth rings in the bones, scientists have determined that moas grew slowly, probably taking ten years to mature and possibly longer before they reproduced. Kiwis only produce one or two eggs a season and this may have been the strategy of the moas too, to produce only a few large young each year. In a land with virtually no predators this strategy worked well - until the ultimate predators arrived in their canoes.
The oldest moa remains are 2.5 million years old. The last moa bones date back to about 1500 CE. It is estimated that the Polynesians arrived a mere two hundred years earlier and in that time, they hunted the large, slow moas to extinction. If the hunters were concentrating on the largest birds, they would have taken out the breeding females first. As they hunted the smaller birds, it is likely that these were immatures who then never had the chance to reproduce. A strategy that had worked for millions of years now worked against the survival of these ancient birds. Unfortunately with its prey gone, the magnificent Haast's Eagle also went extinct at this time.
Moas are related to emus, cassowaries, rheas and ostriches, all ratite species that go back to the continent of Gondwana. When Gondwana broke apart, emus and cassowaries survived in Australia, rheas in South America, ostriches in Africa and the moas and kiwis in New Zealand. Moas differ from the other ratites, which have vestigial wings and wishbones. The moas had neither.
Could there still be some moas somewhere in New Zealand? Not the larger species certainly and probably not on the North Island, which has been extensively cleared. Perhaps there are still pygmy moas hiding in the wild country of Fjordland on the South Island. It would be wonderful if they were there, but it is unlikely given the number of feral mammalian pests now living in New Zealand.