What Was the Biggest Bird Ever? Elephant Birds, Moa and More

The heaviest bird ever: the elephant bird

Elephant birds were giant flightless birds that lived only on Madagascar. The largest species, Aepyornis maximus, stood around 3 m (10 ft) tall. Weight estimates vary a lot, because they are worked out from leg bones: published figures range from about 275 kg (606 lb) to 700–1,000 kg (1,500–2,200 lb). Even the lowest estimate is far heavier than any living bird.

In 2018, a study by James Hansford and Samuel Turvey placed the very largest elephant bird bones in a new genus, Vorombe titan, and described it as the world’s largest bird. Later DNA studies of bones and eggshells found no sign of a separate genus, and many researchers now think these bones simply came from the biggest Aepyornis maximus individuals, possibly females. Either way, the title stays with Madagascar’s elephant birds.

Elephant birds also laid the largest eggs of any known bird. They were about 26–40 cm (10–16 in) long, and the biggest are estimated to have weighed about 10 kg (22 lb), several times more than an ostrich egg. Compare them in How big is an ostrich egg?.

Surprisingly, DNA shows that the closest living relatives of elephant birds are not ostriches but the small kiwis of New Zealand. The two groups split more than 50 million years ago.

The tallest bird ever: the giant moa

The moa were nine species of flightless birds found only in New Zealand. The two giant moa species of the genus Dinornis, one on the North Island and one on the South Island, were the tallest birds known. Females could reach about 3.6 m (12 ft) with the neck stretched upward and weighed an estimated 230–280 kg (510–620 lb).

Moa showed one of the most extreme size differences between the sexes of any bird. In Dinornis, females could be up to twice as tall and three times as heavy as males, and the two sexes were once mistaken for separate species until DNA tests showed otherwise. Unlike every other ratite, moa had no wings at all, not even tiny ones.

The giant moa’s only natural predator was Haast’s eagle, the largest eagle known, which weighed an estimated 10–18 kg (22–40 lb) and hunted adult moa.

Other giant flightless birds

Several other groups of huge, ground-living birds have evolved over millions of years:

• Dromornis stirtoni of Australia, one of the “mihirungs,” lived several million years ago. It stood about 3 m (10 ft) tall and probably weighed more than 500 kg (1,100 lb), making it a rival to the elephant birds for the heaviest bird ever. Despite its ostrich-like shape, it was related to ducks and geese.
• Genyornis, a later mihirung, was over 2 m (6 ft 7 in) tall and lived in Australia until about 40,000–50,000 years ago.
• Terror birds (phorusrhacids) of South and North America were tall, flightless predators with huge hooked beaks, unlike the plant-eating giants above.

The largest flying birds ever

Flying birds face a weight limit that flightless giants do not, but some extinct fliers were enormous.

• Pelagornis sandersi is known from a single fossil found in 1983 during construction at Charleston International Airport in South Carolina. It lived about 25 million years ago, and in 2014 Daniel Ksepka estimated its wingspan at about 6.1–7.4 m (20–24 ft), roughly twice that of the largest living albatross.
• Argentavis magnificens soared over Argentina in the late Miocene, about 6–9 million years ago. Its wingspan is estimated at about 5–6 m (16–20 ft), and at up to about 70 kg (154 lb) it is the heaviest flying bird known.

Today the widest wings belong to the wandering albatross, at up to about 3.7 m (12 ft). See What is the largest flying bird? for the living record holders.

How do the giants compare with ostriches?

The ostrich is the biggest bird alive today, but next to an elephant bird it would have looked slim. A large elephant bird probably weighed at least twice as much as the heaviest ostrich ever recorded.

Why did the biggest birds die out?

The giant birds of Madagascar and New Zealand disappeared soon after people arrived. Elephant birds died out roughly 1,000 years ago, probably because of hunting, egg collecting and changes to the island’s forests and grasslands. In New Zealand, Polynesian settlers arrived around AD 1300, and all moa species were gone by about 1445. With its prey gone, Haast’s eagle also became extinct.

Large, slow-breeding birds that had never met human hunters were especially vulnerable. The same pattern later wiped out the dodo of Mauritius, a much smaller flightless bird of about 10–18 kg (22–39 lb), within a century of sailors landing on its island.

Older giants such as Dromornis, Pelagornis and Argentavis died out long before modern humans, most likely because of changes in climate, habitat and competition over millions of years.