At 10 feet tall, elephant birds, which roamed in the African island of Madagascar thousands of years ago, were the largest birds on Earth before they went extinct between 500 and 1,000 years ago.
A new research now revealed more information about these giant flightless birds.
In a study published in the journal Proceedings of the Royal Society B on Oct. 30, researchers who conducted an analysis of two elephant bird skulls from two species found that these avians were also nocturnal and blind.
"As recently as 500 years ago, very nearly blind, giant flightless birds were crashing around the forests of Madagascar in the dark. No one ever expected that," study researcher Julia Clarke, from the University of Texas Jackson School of Geosciences, said, according to CNN.
The skull of birds fit tightly around their brains so the shape of their skull correlates to the structures of their brain.
Brain reconstruction research showed that the elephant birds' optic nerves, which controlled their eyesight, were incredibly small and almost absent. This means that their vision was poor, making them likely nocturnal creatures.
Study author Christopher Torres, from the University of Texas at Austin, explained that a nocturnal lifestyle tends to be an evolutionary response either when it becomes too dangerous to come out during the day or when a creature's prey comes out at night.
Since elephant birds had no known predator and were herbivorous, nocturnality could have been a trait that they inherited from an ancestor, which they likely shared with kiwis.
Elephant birds were similar to modern-day ostriches and emus, which are big and flightless. These birds, however, are active during the day and have good eyesight.
The findings of the new research suggest that the elephant birds may be more closely related to kiwis in New Zealand which are about the same size as chickens, and are also nocturnal and have poor vision.
"I was surprised that the visual system is so small in a bird this big," bird brain evolution expert Andrew Iwaniuk, from the University of Lethbridge who was not involved in the study, said, according to Eurekalert.
"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."Studies have shown that elephants birds were able to outlive initial contact with humans by many thousands of years. Torres said that the elephant birds being nocturnal may help explain why these birds were able to coexist with humans for this long.