As far as we know, the largest bird of all time was the now-extinct elephant bird. The flightless animal stood over 10 feet tall (3 m), and was native to Madagascar. Little is known about how it lived, although new research surprisingly indicates that it was likely nocturnal, and had little if any eyesight.

Elephant birds died out as a species approximately 500 to 1,000 years ago, the prevailing theory being that humans reduced their habitat and/or over-hunted them. If they did indeed have poor sight, that may have made them particularly easy to hunt.

For the new study, scientists from The University of Texas at Austin performed CT scans on two skulls, each from a different species of elephant bird. Based on the contours of the inside of those skulls, the team was able to create digital models that depicted the shape of the birds' brains. It was found that in both birds, the eyesight-controlling optic lobe was very small – in the larger of two species, it was virtually nonexistent.

The kiwi, which is the closest living relative to the elephant bird, is known to be nocturnal and is virtually blind. Interestingly, its optic lobe is very similar in shape and size (relative to its body) as that of the elephant bird.

"No one has ever suspected that elephant birds were nocturnal," says PhD candidate Christopher Torres, who led the research. "The few studies that speculated on what their behavior was like explicitly assumed they were active during the day."

A paper on the research was recently published in the journal Proceedings of the Royal Society B.

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