Moa were large. Female giant moa (Dinornis genus) were probably over 2 metres tall and heavier than 250 kilograms – significantly more than ostriches or emus. Two extinct birds, the elephant bird (Aepyornis maximus) of Madagascar and ‘the giant duck of doom’ (Dromornis stirtoni) of Miocene Australia, were as tall but bulkier and heavier. Some individuals of Mantell’s moa (Pachyornis geranoides) and the stout-legged moa (Euryapteryx curtus) from the Far North of the North Island were smaller than a large turkey – less than half a metre tall and weighing under 20 kilograms.
Flightless moa were the only birds in the world to lack any vestige of a wing. They had a small bone called the scapulocoracoid, formed from the fused scapula and coracoid. The junction of these two bones is where the humerus of the wing would have been at an earlier stage in evolution.
Moa had rough, furry feathers like a kiwi. The feathers lacked the barbules that usually link the filaments. Little is known about the colour, as feathers have been found only for upland moa. These are dark at the base, lightening to greyish-white at the tip.
Moa had three front-facing toes on each foot, and a small rear toe, often just a spur on the leg. This differs from all other large ratites, which lack a rear toe, and from ostriches, which have just two toes. The moa foot is also distinctive because the tarsus (the scaly part of the leg to which the toes are attached) was very short. In the heavy-footed moa, the breast feathers were barely off the ground.
Head and bill
Moa had small skulls. This is a trait of all ratites, but a 250-kilogram bird would have looked particularly odd with a skull just 23 centimetres long and 12.5 centimetres wide. Their skulls reveal relatively poor eyesight (small orbits), a good sense of smell (enlarged olfactory region), and a very short bill. The bills of different species vary from robust, sharp and pointed to snip branches and flax, to weaker, rounded ones more suited to plucking soft leaves and fruit.
There has been much discussion about the stance of moa. Current wisdom is that like emus, they had a domed back, with the neck rising from the downward slope. The moa’s neck was shorter than any other ratite’s except kiwi’s, and the head was usually held just above the level of the back. Like cassowaries and emus, moa were long birds. Their length was accentuated by their short tarsus. Like emus, they could reach up high to perform threatening displays or gather food.
Little is known about moa breeding. Only about 30 eggs have been found. The largest, attributed to the South Island giant moa (Dinornis robustus), is 24 by 17.8 centimetres, and was found in a Māori burial site at Kaikōura. It is significant as a Māori taonga (treasure) and one of the premier natural history objects of New Zealand. Eggs of other moa species were as small as 12 by 9.1 centimetres, attributed to a stout-legged moa (Euryapteryx curtus).