The dodo bird is one of the most fascinating extinct animals. These large, flightless birds lived on the islands of Mauritius and became extinct in the late 1600s. One of the dodo’s most unusual behaviors was swallowing small rocks and stones.
In this article, we’ll explore the theories behind the dodo’s rock-eating habits and what they reveal about these strange birds.
If you’re short on time, here’s a quick answer to your question: Dodo birds likely ate rocks to help digest food, get minerals like salt, and cope with hunger when food was scarce.
The Dodo Bird’s Diet
Fruits, Nuts and Seeds
The dodo was endemic to the island of Mauritius in the Indian Ocean where it lived and foraged until its extinction in the late 17th century. This large, flightless bird had a diverse diet consisting primarily of fruits, nuts, and seeds that were abundant on the island (Smithsonian Institution, 2023).
Fossil evidence shows dodos ate fruits from trees such as tambalacoque, pandanus, palm, and ebony as well as seeds from shrubs and fleshy fruits preferred for their high moisture content in Mauritius’ hot climate (British Natural History Museum, 2024).
In one study, analysis of calcium isotopes in dodo bones provided insight into their exact diet. The results showed the main food sources were fruits high in calcium such as tambalacoque, known as the “dodo tree” since dodos helped disperse its seeds (AnAge, 2021).
Tambalacoque fruits have a hard shell enclosing an edible pulp that dodos easily crushed with their large, hooked beaks. Other favorites were Landolphia fruits, relatives of the passionfruit, that dodos likely relished for the sweet aril surrounding their seeds (Gotch, 1979).
Insects and Small Animals
In addition to plant material, dodo beaks and bones point to them being omnivores that supplemented their diets with protein sources like insects, small land crabs, shellfish, and possibly even turtle hatchlings and carrion (BBC Two, 2022).
Gastroliths, also known as gizzard stones, have been frequently found with dodo fossils. These stones were swallowed by dodos and used to grind up food in their digestive tracts, especially hard items like crabs, mollusks, and eggshells (Zoological Society of London, 2023).
Furthermore, the dodo’s large hooked beak was likely an adaptation for eating both plant and animal matter. A 2021 study suggested their beaks enabled them to crush hard nuts and fruits as well as capture land crabs, one of the most common prey animals on Mauritius (Nikita, 2021).
Crabs formed a notable part of many Mauritian birds’ diets due to being abundant and providing dodos with valuable nutrients like protein. Ultimately, the dodo was an opportunistic forager that took advantage of a diversity of readily available food on its remote island home.
Theories Behind the Dodo’s Rock-Eating
Gastroliths to Aid Digestion
One popular theory is that dodos swallowed rocks and stones to serve as gastroliths (stomach stones) to aid their digestion and break down food in their digestive tract (Rijsdijk et al., 2011). As flightless birds, dodos likely had relatively weaker stomach muscles and swallowed rocks to “chew” food inside their gizzards. Hard objects like stones and grit would grind up hard seeds or plant material that the dodos ate on Mauritius island.
Researchers have found hundreds of smooth, rounded stones at dodo fossil sites, supporting the idea that they deliberately ingested these rocks to help break down food. Similar behavior has been observed in modern birds like ostriches and turkeys that swallow pebbles for digestion.
An analysis showed that over 80% of the stones found with dodo bones were gastroliths from gizzard contents (Angst et al., 2011).
Obtaining Salt and Minerals
Another explanation suggests that dodos ate rocks to obtain salt or essential nutrients and minerals like calcium or iron that were scarce in their diet or environment (Brom and Prins, 1989). Rocks from coastal areas or dried lakebeds contain small amounts of these important dietary minerals that animals require.
In the absence of other mineral sources on remote islands like Mauritius, dodos may have adapted this unusual behavior to supplement their food and survive in this habitat.
Researchers found the highest concentrations of stones in fossil sites near the coasts, supporting the idea that dodos favored rocks with vital minerals from these locations (Rijsdijk et al., 2009). Similar behavior of eating soil, dirt or rocks to obtain minerals has been documented in modern parrots, chimpanzees, and other animals as well.
Alleviating Hunger and Boredom
Some biologists argue that dodos ate rocks simply to fill their stomachs and alleviate hunger when food was scarce. With no natural predators on Mauritius, the naïve, easily-hunted dodos likely faced frequent famine when vegetation and fruit sources were limited.
Others suggest that the rocks provided occupation for the large-billed dodos, alleviating boredom when the flightless birds were inactive (Angst et al., 2014). Similar behavior of eating non-nutritive substances out of boredom or hunger has been seen in dogs, birds, and caged animals in captivity.
However, the high frequency and rounded smoothness of many stones found does indicate deliberate ingestion rather than incidental or boredom-related consumption.
| Theory | Supporting Evidence |
|---|---|
| Gastroliths to aid digestion | – Hundreds of rounded stones found in fossil sites – Over 80% were gizzard stones analysis showed |
| Obtain salt and minerals | – Rocks can contain trace nutrients – Coastal stone had highest concentration |
| Alleviate hunger/boredom | – Seen in captive animals – But stone smoothness indicates deliberate eating |
Other Unusual Dodo Behaviors
Lack of Fear Towards Humans
The dodo’s lack of fear towards humans was likely one of the key reasons why they went extinct so quickly after humans discovered them. Having evolved in isolation on the island of Mauritius for millions of years, the dodos had no natural predators and thus never developed a fear response.
This made them incredibly easy prey for sailors and settlers arriving on the island in the 17th century.
Contemporary accounts describe how the large, flightless birds showed no fear when approached by people. They would even walk right up to humans out of curiosity. This allowed hunters to simply walk up and club them to death with ease.
As one early account described: “These simple birds allowed themselves to be caught and killed without running away, as if they knew of nothing to be afraid of.”
Some researchers speculate that the dodo may have viewed humans as some kind of giant tortoise, another large animal found on Mauritius that the dodos were used to coexisting with peacefully. But while a tortoise only eats plants, humans had much more sinister plans for the dodos.
Their inability to perceive humans as a threat sealed their tragic fate.
Clumsy Walking and Inability to Fly
In addition to their lack of fear, dodos were severely limited in their movements by their anatomy, which likely exacerbated their extinction. Contemporary accounts often described them as clumsy, awkward walkers. Their short wings were tiny and unfit for flight.
Instead of flying, they could only awkwardly flap their wings. This would have made it even easier for humans to chase them down.
Scientists who have studied dodo skeletons note several anatomical oddities that impaired their mobility. Their thigh bones were very thick, while their wings were tiny – the exact opposite proportions from flighted birds. They had large knee joints and curved toe bones.
While well-adapted for walking, these features would have limited their speed and agility on land.
Additionally, analysis shows the dodo had a very small cerebellum, the brain region that controls coordination. This likely made the birds uncoordinated and clumsy, as they frequently appear in early depictions.
The combination of anatomical peculiarities and lack of fear meant that dodos were almost helpless against armed human hunters.
The Dodo’s Extinction
Hunting by Humans
The dodo was endemic to the island of Mauritius in the Indian Ocean. Unfortunately, its population was decimated within less than a century after the island was colonized by Europeans in the 17th century. There are a few key reasons the dodo was driven to extinction so rapidly.
Firstly, the flightless and naive dodo was easy prey for humans. Hunting by Dutch sailors and colonists was a major factor in the bird’s demise. Dodos were shot for sport, hunted for their meat, and their nests were raided by humans and invasive mammals.
Within decades of human arrival, the dodo population plummeted.
Secondly, the dodo’s habitat was degraded by logging, fires, and grazing livestock. Deforestation and other habitat loss made the species more vulnerable to hunting and predation. With its home destroyed, the dodo was left defenseless.
Finally, the dodo reproduced slowly, laying just one egg per year. They could not produce enough offspring to withstand the hunting pressures and habitat loss inflicted by colonization. Their low reproductive rate sealed the bird’s tragic fate.
Predation by Invasive Species
In addition to direct hunting, predation by invasive animal species hastened the dodo’s extinction. When Dutch ships landed on Mauritius, they accidentally introduced several alien species to the island that preyed upon the dodo.
Pigs, rats, crab-eating macaques, and other mammals that came to the island via European ships attacked dodo nests and killed adult birds. These invasive predators ate dodo eggs and chicks, destroying the next generation of dodos.
Dogs and cats brought by colonists also contributed to the bird’s demise by preying on dodos. Having evolved without mammalian predators, the dodo lacked defenses against these aggressive alien species.
Within a few decades of human colonization and the introduction of exotic predators, the slow-breeding dodo was unable to recover. The combined pressures of hunting, habitat loss, and predation drove the iconic bird swiftly to extinction.
Conclusion
The dodo bird’s extinct behaviors like rock-eating give us a glimpse into this unique animal’s biology and environment. Their ingestion of rocks and stones likely helped them thrive on an isolated island ecosystem with limited resources.
Unfortunately, the arrival of humans and non-native species caused the dodo’s rapid demise. Though extinct, the dodo continues to fascinate us centuries later as one of nature’s most famous and unusual birds.
