According to a newly published study, the dodo was probably not as stupid as people believe. Using modern medical imaging techniques to create scans of the interior of a well-preserved dodo skull, a team of researchers report that the dodo's brain was proportionally similar in volume to that of eight close relatives in the pigeon family. The scans also revealed evidence that the dodo and its closest relative, the extinct island-dwelling Rodrigues solitaire, had a superior sense of smell when compared with the other species examined.

Skeleton cast and model of a dodo (Raphus cucullatus) at the Oxford University Museum of Natural History. (Credit: bazzadaramblerimages/CC BY 2.0).

Skeleton cast and model of a dodo (Raphus cucullatus) at Oxford University Museum of Natural History. (Credit: bazzadaramblerimages/CC BY 2.0).

The dodo, Raphus cucullatus, was a large flightless bird that was first encountered by a boatload of hungry Dutch sailors when they landed on the island of Mauritius in the Indian Ocean during the sixteenth century. Less than 100 years later, the dodo was wiped off the face of the Earth, the victim of hunting, deforestation, nest destruction and competition for food with ship rats, livestock and other invasive pests that people introduced to its island home.

The dodos' gentleness and innocence contributed to their rapid demise and made people view them as being too stupid to live. But as with all creatures that live on remote, predator-free islands for thousands of years, fear is a strange and even an unnecessary concept, so why exactly would they be afraid of humans -- a creature they had never before encountered?

“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 lead author, palaeontologist Eugenia Gold, a research associate and newly-minted PhD from the American Museum of Natural History's Richard Gilder Graduate School, and an instructor in the Department of Anatomical Sciences at Stony Brook University.

This led to dodos going extinct long before most scientists of those times had even seen one.

"Today, they are almost exclusively known for becoming extinct, and I think that’s why we’ve given them this reputation of being dumb,” said Dr Gold in email.

Previous research established that dodos were really big pigeons

What sort of bird, exactly, was a dodo? This was controversial for quite some time (doi:10.1080/08912960600639400), but eventually, scientists realised that the dodo and its closest relative, the extinct Rodrigues solitaire, Pezophaps solitaria, were both members of the pigeon family based upon unique characters of their leg bones that are shared only with pigeons. (Feet and leg bones are the most common surviving pieces of dodos.) Much later, molecular research confirmed this conclusion (doi:10.1126/science.295.5560.1683).

But because museums possess almost no dodo specimens, and because living dodos were not formally studied by scientists, we know almost nothing about them and their lives. Is it possible to learn anything new at all about their life history now? For example, is it possible to even learn whether these iconic birds were as "bird brained" as is commonly believed?

Let's not forget of course, that most people are oblivious to the intelligence of the rock dove, Columba livia, or "common city pigeon"; typically referring to these birds by some variation of the derisive "sky rats" moniker. But throughout history, rock doves were trained to provide valuable services to humans. For example, exploiting their remarkable ability to find their way home, thousands of "homing pigeons" carried messages during wartime, saving tens of thousands of human lives, until the practice was ended in 1957.

More recently, scientists report that rock doves possess mathematical abilities that rival those of rhesus monkeys (doi:10.1126/science.1213357). Equally impressive are their abilities to recognise and memorise specific visual patterns: for example, rock doves never forget a human face (doi:10.3184/175815512X13350970204867), their self-recognition abilities are superior to those of a 3-year-old human (doi:10.1007/s10071-008-0161-4), they can diagnose cancer in mammograms with the same accuracy as a trained medical professional (doi:10.1371/journal.pone.0141357), and they can even be trained to identify different artists and distinct categories of artistic styles (doi:10.1901/jeab.1995.63-165 & doi:10.1007/s100710100112) -- research that won the authors the Ig Nobel Prize in 1995.

Three-dimensional CT scans of a dodo skull reveals it was no "bird brain"

How intelligent were dodos when compared to other pigeon species?

To answer this question, Dr Gold managed to locate a rare well-preserved dodo skull in the collections of the Natural History Museum in London. She used high-resolution computed tomography (CT) scanning to construct a detailed three-dimensional "endocast" of the bird's brain (figure 4A):

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: E Gold et al, doi:10.1111/zoj.12388)

Figure 4. Side views of brain endocasts from the dodo (A), the Rodrigues solitaire (B), and the Nicobar pigeon, Caloenas nicobarica (C). Enlarged olfactory bulbs, labeled “ob,” can be seen in the dodo and the solitaire. The scale bar is 15 millimeters. (Credit: E Gold et al, doi:10.1111/zoj.12388)

Colleagues at the Natural History Museum of Denmark and the National Museums of Scotland created an endocast of the extinct Rodrigues solitaire, Pezophaps solitaria (Figure 4B), another large flightless island-dwelling pigeon, which is the dodo's closest relative.

The same procedure was used to construct an endocast of the Nicobar pigeon, Caloenas nicobarica (Figure 4C), which is the dodo's closest living relative. Endocasts were also created for six other pigeon species, including the rock dove.

When Dr Gold and her colleagues compared the volume of each bird's skull endocast to its body mass, they found that the dodo was “right on the line” -- its brain volume was neither larger, nor smaller, than other pigeons'.

"The dodo's brain size is proportional to its body size, so if we take brain size as a proxy for intelligence, then the dodo was probably as smart as a common pigeon,” said Dr Gold in email. "Of course, there’s more to intelligence than just overall brain size, but this gives us a basic measure.”

But the dodo was still distinct from its relatives.

“It had a number of unusual features (like its size, beak shape, overall goofy appearance), many of which are shared with its closest relative, the Rodrigues Solitaire (probably inherited from their last common ancestor),” said Dr Gold.

Perhaps most remarkably, and in common with the Rodrigues solitaire, the dodo had well-developed and greatly enlarged olfactory bulbs, which is the brain region that is associated with sense of smell.

"[A]nd now we know that they both also had large olfactory bulbs,” added Dr Gold.

This is an unusual trait in birds, which are intensely visual creatures, possessing keen eyesight and enlarged optic lobes.

"We think that their enlarged olfactory bulbs were used to smell out ripe fruit or to find small buried prey,” said Dr Gold.

A few birds, such as the flightless kiwis of New Zealand, have an exquisitely developed sense of smell (and greatly enlarged olfactory bulbs) that help them locate worms and other subterranean creatures that they prey upon. In view of that information, might dodos have been nocturnal hunters as kiwis are?

"Even though some olfactory driven birds tend to be nocturnal (like the kiwi), I do not think these birds are nocturnal based on the size of the optic lobes, which are normal,” said Dr Gold. "Nocturnal birds tend to reduce their optic lobes to almost nothing."

Dr Gold and her team also uncovered another anomaly: the structure of the dodo’s balance organs, the semicircular canals located in the ear, were unique.

"The horizontal canal has a strange bend in it that isn't seen in other specimens, or really in any other bird we've looked at,” said Dr Gold. "We couldn't compare it to the solitaire as we received the endocast from a colleague and not the whole CT dataset of the skull."

What might be the function of the dodo's apparently unique semicircular canals?

"[W]e really aren't certain,” said Dr Gold. "There's nothing to compare it to, so it's hard to hypothesize a biological implication for it."

Despite raising new unanswered questions, modern technologies are providing researchers with fresh insights into the biology and evolution of extinct creatures, such as the mysterious dodo and Rodrigues solitaire.

“It is really amazing what new technologies can bring to old museum specimens,” said co-author Mark Norell, Macaulay Curator of Paleontology and Chair of the Division of Paleontology at the American Museum of Natural History.

“This really underscores the need for the maintenance and growth of natural history collections, because who knows what’s next,” added Dr Norell.

A Nicobar pigeon (Caloenas nicobarica), the closest living relative of the dodo. (Credit: cuatrok77/CC BY 2.0)


Dodos: smarter than most people think | @GrrlScientist


Maria Eugenia Leone Gold, Estelle Bourdon and Mark A. Norell (2016). The first endocast of the extinct dodo (Raphus cucullatus) and an anatomical comparison amongst close relatives (Aves, Columbiformes), Zoological Journal of the Linnean Society | doi:10.1111/zoj.12388

Also cited:

Beth Shapiro, Dean Sibthorpe, Andrew Rambaut, Jeremy Austin, Graham M. Wragg, Olaf R. P. Bininda-Emonds, Patricia L. M. Lee, and Alan Cooper (2002). Flight of the Dodo, Science 295(5560):1683 | doi:10.1126/science.295.5560.1683

Julian P. Hume (2006). The history of the Dodo Raphus cucullatus and the penguin of Mauritius, Historical Biology: An International Journal of Paleobiology 18(2):69-93 | doi:10.1080/08912960600639400

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