Elephant birds, the biggest avians to travel the Earth, were virtually blind

The African island of Madagascar was home to, until relatively recently, the largest birds ever seen. Known as "elephant birds", some species have reached a height of about 10 feet and can weigh up to 1,800 pounds.

The biology of these massive flying birds is largely unknown, but scientists have long thought that they were mostly active by day and had good eyesight, as the vast majority of species in their animal group (ratites) – which includes ostriches, emus, rheas and cassowaries.

However, new research published in the journal Acts of the Royal Society B suggests that the recently extinct birds could have been both nocturnal and virtually blind, much like their closest living relative, the kiwi – a bird the size of a chicken, without a flight, found in New Zealand, which are the only nocturnal ratites.

For their study, a team led by scientists from the University of Texas at Austin digitally reconstructed the skulls of two species of elephant birds – unique to Madagascar – with the help of scans of real fossils. The skulls of the birds being closely related to their brains, the researchers were able to deduce the shape of the organ in the interior. Using their reconstructed skulls, they created digital "casts" of the elephant bird brain, while doing the same for some close relatives, alive and extinct.

The researchers found that the optical lobe – a region responsible for the treatment of vision – in both elephant bird brain casts was tiny, like the kiwi fruit. In fact, the lobe was almost entirely absent in the larger of the two species of elephant birds. This indicates that their eyesight was bad, which suggests that they were nocturnal.

"Discoveries like this give us a great insight into the life of these strange and misunderstood birds," said in a statement Christopher Torres, a researcher from the University of Texas, UT Austin, who led the research. . The few studies that speculated on their behavior explicitly asserted that they were active during the day. "

Illustration of giant nocturnal elephant birds feeding at night in the ancient forests of Madagascar. John Maisano for the University of Texas at the Austin Jackson School of Geosciences.

The casts also indicated that the birds had large olfactory bulbs, areas where the odor is treated, suggesting that they had an increased sense of smell to compensate for their poor eyesight.

There were slight differences between the two species studied, which made it possible to highlight the different habitats in which they resided. For example, the larger of the two had a larger olfactory bulb, a trait associated with living in the forest.

In contrast, the smaller species had a smaller olfactory bulb, which could indicate that they lived in the grasslands. Although still tiny, its slightly larger optical lobe suggests a slightly finer vision, which means it might have been more active at dusk than by the dark of the night.

Andrew Iwaniuk, a professor at the University of Lethbridge and an expert on the evolution of the bird brain, who did not participate in the latest study, said the new findings were intriguing.

"I was surprised to find that the visual system is so small in a bird of this size," he said in a statement. "For a bird of this size, it is really strange to develop a night lifestyle, making it a different ecology from that of its closest relatives or any other species of bird we know."

Elephant birds lived in Madagascar until they died between 500 and 1000 years ago. Although the reasons for their disappearance remain unclear, it is thought that a mixture of habitat loss and human interference played a role.