Dinornithidae

Description

The giant moa of the genus Dinornis may have been the tallest bird to ever live. Females reached about 3.6 meters in height and weighed between 230 and 278 kilograms depending on the estimate, while males were far smaller, at just 34 to 85 kilograms. Their feathers were reddish brown and hair-like, covering most of the body except the lower legs, most of the head, and a small patch of the neck just below the head. Chicks probably had speckled or striped feathers to hide from Haast's Eagles.

The birds had large, powerful feet that could deliver a strong kick. Their long, strong necks and broad, sharp beaks allowed them to eat everything from subalpine herbs to tree branches. The head was small, with a pointed, short, flat, and slightly curved beak. North Island giant moa were generally larger than those from the South Island.

Palaeobiology

For years, researchers suspected that what they thought were different species of moa were actually just males and females of the same bird. Genetic testing of DNA from bones finally proved this. Before 2003, three species of giant moa were recognized: the South Island giant moa, the North Island giant moa, and the slender moa. But DNA showed that every slender moa specimen was male, and every South Island giant moa was female.

This meant the three were really just two species, one living on the North Island and one on the South Island. The South Island species actually contains three distinct genetic groups, so it might eventually be split into more than one species. Giant moa had the most extreme size difference between sexes of any moa: females could be twice as tall and three times as heavy as males.

Reproduction

We can guess how they raised their young by looking at living ratites. The larger females probably competed for the best males, who were likely very territorial. Eggs might have been laid in shared nests in sand dunes, or alone in sheltered spots like hollow trees or beside rocks. The female likely left after laying, while the male sat on the egg for up to three months until it hatched.

Giant moa eggs were huge, about the size of a rugby ball and roughly 80 times bigger than a chicken egg. North Island giant moa eggs measured 19 cm long and 15 cm wide, while South Island ones reached 24 cm by 17.8 cm. These are among the largest bird eggs ever known, bigger than ostrich eggs but smaller than those of the elephant bird.

Despite their size, the shells were incredibly thin: only about 1.06 mm thick for North Island eggs and 1.4 mm for South Island eggs. For comparison, elephant bird eggshells are about 3.7 mm thick. This makes giant moa eggs the most fragile of any bird egg ever measured.

Extinction

For at least 40,000 years before humans set foot in New Zealand, the giant moa lived in a stable ecological balance. Then Polynesian settlers hunted the giant moa and all other moa species to extinction.

Every type of moa was gone by 1500. Most experts agree the Māori were still hunting them early in the 1400s, though some calculations suggest they may have vanished by the mid-1300s. While later European farming—clearing forests and turning land into fields—caused other bird extinctions, the giant moa had already been extinct for 300 years by the time Europeans arrived.