Scientific name: Several species Scientific classification:
When did it become extinct? Estimates for the disappearance of the moa vary, but it is thought they became extinct in the 1500s. Where did it live? The moa were found only in New Zealand.
The elephant birds (see the earlier entry in this chapter) were not the only giant birds that roamed the earth in quite recent times. Thousands of miles to the east of Madagascar, the islands of New Zealand were once home to several species of large bird, the largest of which was taller than the elephant birds, although much more slender. Collectively, these birds were known as moa (a Polynesian word meaning "fowl"), and they had lived on the islands of New Zealand for tens of millions of years. The only mammals that had managed to reach New Zealand were bats, so the islands were free of any large ground-based predators or herbivores, absences which allowed the ancestors of the moa to evolve in unique ways. First, as there were no mammalian predators, flight was an unnecessary extravagance, especially as food was so abundant. Flight limits the maximum size a bird can ever be, and so without this limitation, the moa grew to huge sizes Sec-
Moa—Several species of moa once inhabited the islands of New & &
Zealand. They ranged in size from 1-m-tall, 25-kg birds to 4-m-tall, ond, as there were no mam-275-kg giants. (Renata Cunha) malian herbivores in New
Zealand, the moa evolved to fill this gap, taking on the ecological role that animals such as deer fill in many other parts of the world.
Today, between 10 and 15 species of moa are recognized by scientists from their remains, but it is impossible to know exactly how many species of these interesting birds once inhabited the islands of New Zealand. Some experts have suggested that there could have been as many as 24 species of moa. The smallest species were around 1 m tall and weighed around 25 kg, while the biggest species, Dinornis robustus, on South Island, and Dinornis novaez-elandiae, on North Island, were enormous, at around 4 m at their full height and 275 kg in weight. Interestingly, moa skeletons and reconstructions are almost always shown standing upright, but scientists now think that they walked around with their neck held more or less horizontal to the ground, but they could have probably risen to their full height when they needed to. All the moa were covered in very fine feathers, resembling hair—much like the
kiwis—and all of them had very robust legs ending in powerful, clawed feet. Much of the head, throat, and lower legs were featherless. The wings of the moa had become so useless that they had shrunk away to almost nothing and only remained as small vestigial flaps beneath the hairlike plumage.
The moa were all herbivores, and as they diversified into a range of species, they probably fed on different plants in different habitats. Some of the species may have grazed the plants in the lowlands, while other species nibbled low-growing herbs in the uplands. Although New Zealand was once free of mammalian predators, the moa did have an enemy in the shape of Haast's eagle (see the later entry in this chapter), an impressive aerial predator that probably assaulted the moa from the air and killed them with its powerful crushing talons. The only real defense the moa had against this predator were their powerful legs, which bestowed them with a good turn of speed when the need arose.
The bones and bits of mummified moa tissue that have been found tell us where the animal lived and what the animal looked like, but it can only partially illuminate the life of these long-dead animals. Like other birds, the moa laid eggs—big eggs (the biggest moa egg has the same capacity as about 100 chicken eggs)—and as building a nest up a tree was completely out of the question, these must have been deposited on the ground, probably in a simple scrape or on a mound of gathered vegetation. Unusually, the female moa was much larger that the male, and this suggests that they must have had some interesting breeding system the likes of which we can only guess, but it is reasonable to assume that the female protected a territory and attracted her suitors—a reversal of what is seen in many bird species, where the male has to attract mates.
What happened to these feathered giants? The simple answer is humans. Polynesians (called Maori), on their seafaring craft, reached New Zealand around a.d. 1300, and their effect on the plants and animals of these islands was dramatic. We can only imagine what these people thought when they reached New Zealand, but they must have been at sea for a long time without charts and no idea of their destination, so for them to come across these verdant, volcanic islands stocked with all sorts of food must have been cause for celebration. There is evidence to suggest that these migrants started wildfires, maybe to clear areas for the cultivation of crops or perhaps as a way of driving prey animals out from cover. They also hunted the moa directly, and what with the combined effects of this and habitat loss, the moa were doomed. The moa were probably long-lived birds, and it has been shown that they only reached full size at about the age of 10, with several more years passing before they reached sexual maturity. Therefore any factors that had an effect on the number of adults in the population, such as hunting and habitat loss, had a drastic effect on the population as a whole. It has recently been speculated that moa populations were on the decline before the arrival of humans, possibly due to disease transported by migrating birds gone astray or even due to explosive volcanic activity. Regardless of the possibility of a dwindling population, the moas were wiped out around 160 years following the arrival of humans—a startlingly short period of time and yet another demonstration of how destructive our species can be.
♦ It was once thought that the closet living relatives of the moa are the kiwis, but the current view is that they were more closely related to the emu of Australia and the cassowary of Australia and New Guinea.
♦ The ancestors of the moa are thought to have walked across to New Zealand when it was still part of the massive landmass known as Gondwanaland. Over tens of millions of years, tectonic forces rafted the lands of New Zealand apart until they became an isolated group of islands. The ancestors of the kiwis are thought to have flown to New Zealand after it had become separated.
♦ New Zealand is an oceanic archipelago that consists of two large islands, North Island and South Island, as well as many smaller islands. The land area and the diversity of the habitats on these islands provided the original inhabitants with a wealth of niches into which to evolve, and birds became the rulers of this realm.
♦ Since the arrival of humans to New Zealand, more than 58 species of native birds have become extinct.
♦ All birds evolved from small dinosaurs about 155 million years ago in the late Jurassic period. Ratites, the group of birds to which the moa belonged, evolved in Gondwa-naland in what we know as South America. As this supercontinent was wrenched apart over millions of years into the landmasses with which we are familiar today, the ratites evolved into the moa and kiwis of New Zealand, the elephant birds of Madagascar (see the entry earlier in this chapter), the emu of Australia, the cassowary of Australia and New Guinea, the ostrich of southern Africa, and the rheas of South America.
Further Reading: Worthy, T. H., and R. N. Holdaway. The Lost World of the Moa. Bloomington: Indiana University Press, 2002; Turvey, S. T., O. R. Green, and R. N. Holdaway. "Cortical Growth Marks Reveal Extended Juvenile Development in New Zealand Moa." Nature 435 (2005): 940-43; Bunce, M., T. H. Worthy, T. Ford, W. Hoppitt, E. Willerslev, A. Drummond, and A. Cooper. "Extreme Reversed Sexual Size Dimorphism in the Extinct New Zealand Moa Dinornis." Nature 425 (2003): 172-75; Holdaway, R. N., and C. Jacomb. "Rapid Extinction of the Moas (Aves: Dinornithiformes): Model, Test, and Implications." Science 287 (2000): 2250-54.
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