The volcanic island of Mauritius, located in the Indian Ocean about 500 miles east of Madagascar, remained uninhabited (by humans, at least) until 1598, when Dutch explorers took possession of it. Long before that, however, the island was the only known habitat of the large, flightless birds known as dodo birds (Raphus cucullatus). Having never seen humans before, the dodos on Mauritius showed no fear of the newly arrived sailors, and were easily hunted or herded onto ships and used as a readily available food source. By 1662, the dodo bird was extinct.
Scientists don’t know that much about the dodo’s biology, as specimens of the long-extinct bird are rare. It was the sad truth of their all-too-quick extinction that most likely fueled the popular stereotype of dodos as stupid creatures—bumbling, overweight birds that couldn’t even fly. The new study, published this week in the Zoological Journal of the Linnean Society, suggests that this characterization may be unfair, and that dodos might actually have been reasonably intelligent.
The study’s lead author is Eugenia Gold, a research associate and recent graduate of the American Museum of Natural History’s Richard Gilder Graduate School, and an instructor in the Department of Anatomical Sciences at Stony Brook University. Gold’s team used high-resolution computed tomography (CT) scanning to examine the well-preserved skull of a dodo bird in the collections of the Natural History Museum in London. The researchers then used the scans to build virtual brain endocasts, which allowed them to determine overall brain size as well as the size of various structures within.
Scientists have determined through DNA analysis that the dodo belongs in the dove and pigeon family, and Gold’s team also used CT scanning on the skulls of seven species of pigeon. These included Columba livia, the common pigeon most of us encounter every day on city streets, as well as more exotic species. Also for purposes of comparison, Natural History Museum of Denmark and the National Museum of Scotland sent Gold an endocast for the dodo’s closest relative, the island-dwelling bird Rodrigues solitaire (Pezophaps solitaria), which was recently driven into extinction by human activity.
When comparing the size of the birds’ brains with their body sizes, the researchers found the dodo’s brain to be comparable in size to that of a modern pigeon, and right in line with its body size. As Gold told Phys.org: “It’s not impressively large or impressively small—it’s exactly the size you would predict it to be for its body size. 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.”
In addition to a nicely proportionate overall brain size, the researchers also found that both the dodo and the solitaire had a large, differentiated olfactory bulb. In general, birds depend on sight much more than smell, and tend to have larger optic lobes than olfactory lobes. But the new findings suggest that because dodos and solitaires were closer to the ground, they probably relied more on their sense of smell to find their food. Scientists think dodos dined on fruit, in addition to small land vertebrates and marine animals such as shellfish.
This fruit-based island diet may have been one of the things that indirectly led to the dodo bird’s eventual extinction. It’s widely believed that the dodo originally migrated to Mauritius by flight, but adapted over millions of years to its isolated island way of life, with its lack of predators and large quantity of fruit located on or close to the ground. Flightlessness and gigantism were two of the traits they adapted. With no experience of humans, the dodo didn’t show any fear of the Dutch sailors when they arrived, making them an easy target. In addition to acting as predators themselves, the Dutch also introduced non-native animals such as dogs, pigs and rats to the island, all of which helped spell disaster for the dodo bird.