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Elephant Birds, The Biggest Avians to Walk the Earth, Were Practically Blind

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The African island of Madagascar was, until relatively recently, home to the largest birds that ever lived. Known as “elephant birds,” somes species grew to heights of around 10 feet tall and could weigh up to 1,800 pounds.

The biology of these massive, flightless birds is mostly unknown, but scientists have long thought that they were primarily active in the daytime and had good eyesight like the vast majority of species in their animal group (ratites)— which includes ostriches, emus, rheas, and cassowaries.

However, new research published in the journal Proceedings of the Royal Society B suggests that the recently extinct birds may have been nocturnal as well as practically blind, much like their closest living relative, the kiwi—a chicken-sized, flightless bird 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—which are unique to Madagascar—using scans of real fossils. Because bird skulls wrap tightly around their brains, the researchers were able to infer the shape of the organ inside. Using their reconstructed skulls, they created digital “casts” of the elephant bird brains, while also doing the same for some close relatives, both living and extinct.

The researchers found that the optic lobe—a region responsible for processing vision—in both elephant bird brain casts was tiny, like the kiwi. In fact, the lobe was almost entirely absent in the larger of the two elephant bird species. This indicates their eyesight was poor, making it likely that they were nocturnal.

“Discoveries like these give us tremendous insights into the lives of these bizarre and poorly understood birds,” Christopher Torres, a researcher from UT Austin, who led the research, said in a statement. “No one has ever suspected that elephant birds were nocturnal. The few studies that speculated on what their behavior was like explicitly assumed they were active during the day.”

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

The casts also indicated that the birds had large olfactory bulbs—regions where scent is processed—suggesting they had a heightened sense of smell to offset their poor eyesight.

There were slight differences between the two species studied, which has helped to shed light on the different habitats that they both resided in. For example, the larger of the two had a bigger olfactory bulb—a trait which is associated with living in forests.

In contrast, the smaller species had a smaller olfactory bulb, possibly indicating that it lived in grasslands. While still tiny, its slightly larger optic lobe suggests it had somewhat keener vision, which means it may have been more active at dusk rather than the pitch black of night.

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

“I was surprised that the visual system is so small in a bird this big,” he said in a statement. “For a bird this large to evolve a nocturnal lifestyle is truly bizarre and speaks to an ecology unlike that of their closest relatives or any other bird species that we know of.”

Elephant birds lived in Madagascar until becoming extinct somewhere between 500 and 1,000 years ago. While the reasons for their demise remain unclear, a mixture of habitat loss and human interference is thought to have played a role.

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