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Study Reveals Dodo Birds Not Stupid as Previously Thought

Dodo

The dodo, an extinct bird popularly recognized for its stupidity, may actually have been fairly smart, or at least as smart as a common pigeon. This finding is based on a study led by Eugenia Gold, an instructor in the Department of Anatomical Sciences at Stony Brook University, and published in the Zoological Journal of the Linnean Society.

Dodo Model, PC #5338
A model of a dodo bird (American Museum of Natural History/C. Chesek)

The dodo (Raphus cucullatus) was a large, flightless bird that lived on the island of Mauritius in the Indian Ocean. They were last seen in 1662. In the paper, “The first endocast of the extinct dodo and an anatomical comparison amongst close relatives,” Gold and colleagues find that the overall size of the dodo’s brain in relation to its body size was on par with its closest living relatives: pigeons — birds whose ability to be trained implies a moderate level of intelligence. The researchers also discovered that the dodo had an enlarged olfactory bulb — the part of the brain responsible for smelling — an uncharacteristic trait for birds, which usually concentrate their brainpower into eyesight.

“When the island was discovered in the late 1500s, the dodos living there had no fear of humans and they were herded onto boats and used as fresh meat for sailors,” said Gold, whose research centers on brain evolution between flying and non-flying birds. “Because of that behavior and invasive species that were introduced to the island, they disappeared in less than 100 years after humans arrived. Today, they are almost exclusively known for becoming extinct, and I think that’s why we’ve given them this reputation of being dumb.”

Despite this reputation for stupidity, she adds, most aspects of the dodo’s biology are still unknown. This is partly because dodo specimens are extremely rare, having disappeared during the nascent stage of natural history collections.

To examine the brain of the dodo, Gold used a well-preserved skull from the collections of the Natural History Museum, London, and imaged it there with high-resolution computed tomography (CT) scanning. She used the CT scanning method at the American Museum of Natural History in New York to digitize the skull of the dodo and seven other pigeons, ranging from the common pigeon to exotic varieties. She also acquired the reconstructed brain of the dodo’s closest relative, the Rodrigues solitare, another giant, flightless and extinct bird.

Side views of brain endocasts from the dodo (A), the Rodrigues solitaire (B), and Caloenas nicobarica (C), a type of pigeon. Enlarged olfactory bulbs, labeled “ob,” can be seen in the dodo and the solitaire. The scale bar is 15 millimeters. Credit: American Museum of Natural History/ E. Gold
Side views of brain endocasts from the dodo (A), the Rodrigues solitaire (B), and Caloenas nicobarica (C), a type of pigeon. Enlarged olfactory bulbs, labeled “ob,” can be seen in the dodo and the solitaire. The scale bar is 15 millimeters. (American Museum of Natural History/E. Gold)

“I digitally filled in its braincase to recreate and endocast of the dodo,” explained gold. “We also performed a regression of brain volume to body size and found that the dodo has a brain completely in proportion to its body size.”

When comparing the size of the birds’ brains to their body sizes, Gold and collaborators found that the dodo was “right on the line.”

“It’s not impressively large or impressively small — it’s exactly the size you would predict it to be for its body size,” Gold said. “So if you take brain size as a proxy for intelligence, dodos probably had a similar intelligence level to pigeons. Of course, there’s more to intelligence than just overall brain size, but this gives us a basic measure.”

Their findings also revealed that both the dodo and the Rodrigues solitaire, which was driven to extinction in the late 1700s by human activity, had large and differentiated olfactory bulbs. In general, birds depend much more on sight rather than smell to navigate through their world, and as a result, they tend to have larger optic lobes than olfactory bulbs. The authors suggest that, because dodos and solitaires were ground-dwellers, they relied on smell to find food, which might have included fruit, small land vertebrates, and marine animals like shellfish.

The researchers also discovered an unusual curvature of the dodo’s semicircular canal—the balance organs located in the ear. However, they do not have a good hypothesis for this atypical feature.

The research was supported in part by the American Museum of Natural History, the National Science Foundation, the Macaulay Family Endowment, a Marie Curie Intra European Fellowship, and the Carlsbergfondet.

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