The dodo has long been a symbol of human-caused extinction, to the point that this doomed bird has been elevated to the status of an icon and the subject of public and scientific interest alike. While the dodo was hunted by humans, it is believed that the introduction of invasive species such as rats, cats, deer and monkeys to the Mauritius, once the dodos home, were the actual cause of its extinction.
The last dodo was seen in the wild in 1662, less than a hundred years after dodos were first discovered, and the ill-fated bird’s quick descent into oblivion gave 17th century naturalists insufficient time to record its ecology and better understand the life cycle of this fascinating animal.
Delphine Angst and her team of researchers in Cape Town University have set out to rectify this. Using histology, the examination of minute cells and tissues, the researchers have examined a set of 22 bones, all but one being from the hind legs of several dodos of different sexes and stages of development in order to uncover more about the dodo. This was a rare and exciting opportunity as many of the dodo specimens had been lost or destroyed during the Victorian era.
Analysing Lines of Arrested Growth (LAGs) in the dodo bones, which are thought to be as a result of periods of food shortage, has allowed Angst and her team to read the bones in a similar way to how the rings in tree trunks are studied. This allows the researchers to use them to assign a yearly life-cycle to the dodos.
In Mauritius, the months of November to March have a harsh climate with heavy winds and rains. As a result, food is scarce. Angst worked from the assumption that the LAGs in the bones’ tissue represent these months of sparse food. The researchers looked for signs of the periods that formed the dodo’s annual cycle in the bone built in between the yearly LAGs.
Originally, it had been proposed that the ovulation period for the dodos occurred immediately after the summer months. This was due to a report from 1602 from Captain Van Westzanen describing the dodo’s meat as tasty. It was assumed that it being tasty was a result of the abundance of food and the dodos would have evolved to reproduce during these times.
However, Angst and her team have found differently. They discovered that female dodos produced a type of bone tissue specifically used to make shells for their eggs. By looking at the female dodo bones, it was also possible to calculate in what period the dodos carried their young. The evidence suggests that dodo’s laid their eggs midway through the calmer months, around August. The eggs then hatched in September and grew rapidly to reach sexual maturity before the cyclone season started again in November to January.
Although they reached their full mass within the first year, their bones continued to mature over several years like many modern birds. This strategy was probably not a weakness due to the lack of predators on the island. The size of the female bones, distinguished by the bone tissue specifically used in ovulation, did not differ greatly from the male bones suggesting that the males and females did not differ physically either.
Historical accounts of the dodo’s appearance have always been a source of contradiction and discrepancy. With sailors in the 16th and 17th century describing them as having grey or black plumage and others stating they had only a few feathers. Dodos moulting would explain these discrepancies in the historical reports of sailors. Growing new feathers requires more calcium than usual and this calcium came from inside the bones; penguins of today use the same strategy when they moult.
Angst and her team have reported that dodo bones do indeed show that they moulted, resulting in different appearances depending on the time of year. This degeneration was evident in some of the bones that Angst and her team were studying. The samples with evidence of moulting had a small layer of bone deposit over the LAGs, suggesting that they moulted soon after the summer months.
Much remains to be discovered about the dodo. Angst and her team will be striving to trace more of the life cycle of the dodo and how it lived before human intervention, but the findings of Angst and her team represents the exciting potential of learning more about extinct animals. Evolutionary scientists allow us to base our understanding of them on the scientific investigation of physical evidence, rather than sometimes dubious or confusing historical accounts – giving us a more realistic view of these extinct animals’ lives and exciting possibilities for future rediscovery of the past.