Moas (Dinornithidae)

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Moas

(Dinornithidae)

Class Aves

Order Struthioniformes

Suborder Dinornithes

Family Dinornithidae

Thumbnail description
Large, flightless cursorial birds with no visible wings, long legs, long necks, and four toes

Size
3–12 ft (0.9–3.7 m); 48–506 lb (22–230 kg)

Number of genera, species
6 genera; 10 species

Habitat
Forest, woodland, heath, and grassland

Conservation status
Extinct

Distribution
New Zealand

Evolution and systematics

Moas belong to the group of large, flightless birds known as ratites. Ratites have a distinctive palate, and a sternum (breastbone) with no keel, so there is no anchor for the strong musculature needed for powered flight. The origin of these birds has recently been clarified by the discovery of numerous good fossils in North America and Europe. Ratites were once thought to have a southern origin in the ancient continent of Gondwana, but new fossil evidence shows that flying ratites inhabited the Northern Hemisphere in the Paleocene and Eocene, 40–70 million years ago. The present Southern Hemisphere distribution of ratites probably resulted from the spread of flying ancestors of the group from the north.

The earliest remains of moas in New Zealand are from the Upper Pliocene, about 1.5 million years ago. By then they were recognizably moas, but it is thought that the two subfamilies—the tall, graceful Dinornithinae and the short, stout-bodied Anomalopteryginae—may be descended from two different flying ratites that invaded New Zealand during the Tertiary. Many different classifications have been proposed for moas; some authors list as many as 27 species, others only 10. The lower figure is adopted here, following a detailed review by Atholl Anderson, because many earlier classifications depended on small differences in subfossil bone size and shape that could be due to sexual dimorphism or age differences.

Physical characteristics

There are no accounts of living moas. All information is derived from subfossil material recovered from swamps, caves, and river beds. Moas were very large, flightless birds with long necks and long legs. Unlike surviving large ratites, the tibial bone of moa legs was longer than the tarsus, and they moved slowly. Except for bats, no mammals inhabited New Zealand, so moas had no predators before the Polynesians arrived and no need to flee swiftly. The height of the birds (to the back) was 3–12 ft (0.9–3.7 m) and they weighed 48–506 lb (22–230 kg). The three Dinornis species and Pachyornis elephantopus were the largest, weighing 257–506 lb (117–230 kg). Surviving feather and skin fragments indicate that, apart from the legs, the birds were fully feathered, although they had no visible wings. Each feather was double, with a well-developed aftershaft, and was brownish, sometimes with pale edging.

Evidence indicates that in at least some species females were larger than males.

Distribution

Moas lived only in New Zealand. Five species (Anomalopteryx didiformis, Euryapteryx geranoides, Dinornis struthoides, D. novaezealandiae, and D. giganteus) were common to North and South Island, two have been found only on North Island (Euryapteryx curtus and Pachyornis mappini), and three only on South Island (Megalapteryx didinus, Emeus crassus, and P. elephantopus). At least one species (Euryapteryx geranoides), and possibly two, also lived on Stewart Island. There is debate about the total numbers of moas, with estimates ranging from millions to thousands. Using the most recent evidence, Atholl Anderson has argued that if all 10 species were combined, there were probably only tens of thousands in total—twice as many in South Island as in North Island—with the greatest concentration on the eastern side of South Island.

Habitat

Moas apparently lived in all New Zealand environments, using coastal dunes, forest fringes, podocarp (seed-producing conifers) forests, beech forests on limestone, shrubland, and grassland up to 6,600 ft (2,000 m). A. didiformis, D. struthoides,

and D. novaezealandiae lived in dense lowland conifer and broad-leaved forest, and beech forest. M. didinus lived only in high-altitude beech forest. Emeus crassus, Euryapteryx species, Pachyornis species, and D. giganteus lived in the lowlands—dunelands, forest fringes, and forest, shrub, and grassland mosaics.

Behavior

Most moas were probably diurnal, living in small groups rather than large flocks. There is no hard evidence about their daily lives.

Feeding ecology and diet

A number of moa gizzards have been found and analyzed, showing that the birds fed on plants, taking seeds, twigs, and leaves from different species. Nineteen gizzards from two different sites showed that the birds took plants that grew in the forest and those from open country, suggesting they often fed along the boundary between the two environments. About 80% of the material was twigs, but seeds and leaves were also abundant. It may be that the tough twigs stayed longer in the gizzard than other plants and were over-represented in the sample.

It is now clear that moas did not exist solely on ferns, as some early authors suggested, but used a number of different plant species as food. Seeds of the shrub Comprosma and the tree Podocarpus were abundant, but 29 different species were represented in 19 samples. All gizzards contained pebbles, up to 11 lb (5 kg) in a large Dinornis. From the nature of these pebbles, which were the kinds of rock found where the gizzard was collected, it can be deduced that moas were sedentary. Had they been migratory or nomadic, pebbles in the gizzard would have included rocks of many kinds because such pebbles remain in the gizzard for months, and would have reflected different landscapes. More information will gradually come to light about the diversity of the moa diet, because the shapes and sizes of their bills differ considerably, suggesting that various species must have selected different foods.

Reproductive biology

Moas laid small clutches, perhaps only one egg. It is thought, on very slight evidence, that males incubated, as is the case in most other ratites, but nothing is known of their routines, not even the incubation period. Some supposed nests of sticks around scrapes in the ground have been found in caves and rock shelters associated with egg shell fragments. The eggs are large—up to 9 in (23 cm) long and 7.6 in (19.5 cm) wide—and green, at least in some species.

Conservation status

Extinct. The last moas probably died out in the seventeenth century.

Significance to humans

Moa is the Maori word for a group of large, flightless birds. A great deal of thought has been given to the interaction of Maoris and moas. More than 300 sites have been identified at which moas were butchered by Maoris, some (according to carbon dating) as old as a.d. 1000. The sites provide evidence that the Maoris killed and ate moas systematically. Some sites are very large, but Atholl Anderson has analyzed their location and size to show that they fall into two classes. Sites near the coast are adjacent to large rivers and usually contain remains of many moas. This suggests that expeditions were made up river and the birds brought downstream by boat for butchering. Small sites are mostly in the mountains, or where water transport would not be available, suggesting that they represent the catch of one hunting party, the birds being butchered on the spot and probably eaten there too. Moas would provide a very valuable protein resource in a land where other game was scarce.

The evidence of such extensive hunting has been used to suggest that moas were hunted to extinction. However, the Maoris also cleared the land, mainly by burning vegetation; such habitat alteration may have contributed significantly, perhaps fatally, to the extermination of many species. There are other puzzles, too. Many moa bones are found aggregated in beds of former and existing swamps. There is much to discover about the interactions between moas and Maoris. It is known that Maoris used moa skins as cloaks and carved tools from the bones. It is surprising, considering the significance the birds must have had, how little mythology about them has survived.

Resources

Books

Davies, S. J. J. F. Ratites and Tinamous. Oxford: Oxford University Press, 2002.

Anderson, A. Prodigious Birds, Moas and Moa-hunting in prehistoric New Zealand. Cambridge: Cambridge University Press, 1989.

Periodicals

Anderson, A. "Habitat Preferences of Moas in Central Otago, A.D. 1000–1500, According to Palaeobotanical and Archaeological Evidence." Journal of the Royal Society of New Zealand 3 (1982): 321–36.

Rudge, M. R., ed. "Moas, Mammals and Climate in the Ecological History of New Zealand." New Zealand Journal of Ecology Supplement 12 (1989): 1–169.