Less than a thousand years ago, a bird roamed Madagascar that stood as tall as an elephant. You may have heard of the elephant bird — it's the largest bird species to ever live. New research has presented evidence that this famous extinct bird was nocturnal and had poor vision.
The scientists reconstructed the shape of the bird's brain based on scans of its skull, and found that it seemed to have small optic lobes, or nerves in charge of vision. In fact, the bird's brain looked quite a bit like its distant cousin, the flightless, nocturnal kiwi. So perhaps the elephant bird, too, was nocturnal.
"The only birds that have lost their optic lobes were flightless, nocturnal birds," study author Christopher Torres, a graduate student at the University of Texas at Austin, told Gizmodo. "The implications of nocturnality are a big surprise."
Elephant birds are a much-discussed species, given their immense size and the fact that, since they only went extinct a few hundred years ago, some humans must have interacted with them. The biggest ones are presumed to have been the height of an elephant and the weight of a horse. They're cousins of birds like the emu, cassowary, ostrich, and kiwi.
The researchers took x-ray images of two species of elephant bird to reconstruct the insides of the birds' heads. They did the same for a songbird and a shorebird for comparison. The elephant birds had "extremely reduced" optic lobes compared to other birds, according to the study published in the Proceedings of the Royal Society B. The elephant bird's cousin, the kiwi, also has small optic lobes, so the researchers inferred that the elephant bird, too, could be nocturnal.
This paper is an inference about an extinct bird, so it's hard to tell what the birds were really like, and if they were nocturnal, how they managed to get around. "There's still major questions about what the advantages were of being nocturnal and which sensor system filed that gap," said Torres.
Harold Zakon, a UT Austin professor in neuroscience and integrative biology who was not involved in this study (but who works closely with its authors), felt the experiment was as solid as possible without having an actual brain to look at. It made him wonder why the bird might be nocturnal, "since it certainly would not have to fear any day-active predators," at least until humans showed up, he told Gizmodo. Perhaps the two elephant bird species evolved from a shared nocturnal ancestor.
This research adds more mystery to the strange, extinct elephant bird, and perhaps changes how we imagine them. "It will force us to rethink the role they played on Madagascar at the time," said Torres, "and how ancient humans interacted with them."