DODO BIRD: CHARACTERISTICS, CAUSES OF EXTINCTION, HABITAT, BEHAVIOR - BIOLOGY - 2024

The dodo bird (Raphus cucullatus) is a species of bird that was extinct in the mid-17th century, included in the order Columbiformes. This bird belongs to the Columbidae family like current pigeons, however, it forms a separate subfamily called Raphinae made up of flightless birds.

The dodo was a large bird, adapted to live on land and with body modifications that prevented it from flying. Despite having coexisted with man, there are few records in ecology. In fact, since its discovery in 1598 by Dutch sailors, information was only collected until a century later.

Side view of the reconstructed face of Raphus cucullatus By Musée d'Histoire Naturelle de Lille

As is typical in other flightless birds, gigantism in the dodo is likely due to various physiological changes, a longer life span as a result of the absence of natural predators, higher thermodynamic efficiency, and management of the fasting capacity due to the temporality of resources.

Initially, these characteristics caused confusion about the phylogenetic location of the dodos. These were related to birds of the order Struthioniformes (Ratites), however, morphological evidence linked this bird with Pezophaps solitaria, the Rodrigues solitaire, a species of columbiform bird that is also extinct.

Both birds were continuously mobilized within different groups within the order Columbiformes, including an independent Rhaphidae family outside the Columbidae family. Despite this, the molecular study of the family assigned both species to the Columbidae family.

Currently, the closest living relative of the dodo is the Nicobar pigeon (Caloenas nicobarica), which inhabits some islands of the Indonesian archipelago and the island of Nicobar.

General characteristics

The actual appearance of the dodo is one of the questions that has caused the most controversy in the literature. Most descriptions are based on features observed in drawings and works by explorers.

The dodo bird, like other extinct columbiform birds such as Rodrigues' solitaire (Pezophups solitaria), were characterized by being birds of large body size up to one meter in height. The forelimbs and the pectoral muscles related to flight were considerably reduced due to their terrestrial habits.

Reconstructed dodo skeleton By KKPCW

The dodo's skull was large, pear-shaped and with a prominent beak. The beak of these birds was quite large and strong, with the anterior area somewhat widened and the tip arched.

In the forelimbs there was a characteristic differential shortening of the wing elements, changes in the sternum, as well as in the angle between the scapula and the coracoid. On the other hand, the dodo's femurs were disproportionately long, with short tarsal-metatarsals and elongated toes.

Body weight estimates were made from femur measurements for columbid birds and adaptations made for non-flying birds that accumulate seasonal fat. These indicate that the male dodo weighed around 21 kg while the female weighed approximately 17 kg.

Coloration

The coloration of the dodo has been subject to debate, as the historical accounts are variable and there are many discrepancies in the descriptions. Several coloration patterns attributed to different states during the molting process and type of plumage have probably been described.

Among the descriptions, it is indicated that the dodo had black feathers in the area of ​​the wings and a tail with short, grayish, laughing feathers. Other descriptions indicate that they had a dark grayish to blackish coloration with feathers of the down type all over the body.

Plastic model of the dodo Raphus cucullatus By Jebulon

The molting behavior of the dodos probably occurred after the period of food scarcity and the reproduction processes, between the months of March and July. This same molting pattern can be observed in native birds that still persist on the island of Mauritius.

The legs were probably yellow, given the various illustrations made by explorers.

Causes of extinction

The exact date of extinction of this bird is doubtful, although the last time a specimen was reported came from an islet offshore off the island of Mauritius in 1662. This sighting was made by Volkert Evertsz, when the species was already considerably weird. Another report comes from a slave in 1674 near the same area, although this sighting is more in doubt.

Additionally, some predictions based on current statistical tools indicate that the species reached its end in 1690, about 30 years after the last confirmed sighting.

In any case, the dodo became extinct very quickly since it was discovered. Much of the reports after this date can be attributed to confusion with other species of flightless birds also extinct on the island of Mauritius, which persisted slightly longer than Raphus cucullatus.

The causes of the extinction of this strange-looking bird are attributed exclusively to the effect caused by anthropogenic activities.

Hunting

In the first place, after the arrival of man on the island of Mauritius, many specimens, of all ages, were hunted for meat consumption.

This occurred due to the fact that these birds had a very docile behavior and were large, making them desirable prey and very easy to capture to resupply the supplies of boats that arrived on the way to the island of Mauritius.

On the other hand, the eggs were constantly looted by the sailors also for consumption. Many runaway slaves hiding in the interior of the island hunted dodos and consumed their eggs as a survival measure.

This has been demonstrated due to the finding of a large number of bones of these birds in caves and shelters in steep areas that were not the ideal habitat for these birds.

Species introduction

Additionally, with the arrival of man, a group of mammals previously absent on the island were introduced, with the exception of some species of endemic flying foxes.

These animals, which include domestic companions such as dogs and cats, livestock such as pigs, and others such as deer, primates, and rodents, also played a role in the disappearance of dodo populations.

As the dodos had no natural predators, they probably did not cope with these new elements introduced into their natural habitats when they looted nests. There are no reports of dodos defending their clutches.

Low reproductive rate

Although the reproductive frequency of these birds is not known with certainty, it is likely that they presented a reproductive decline.

Females have been documented to lay only one egg during each season. In this sense, the loss of an egg before the new introduced predators and the human hand, implies strong population declines in the short term.

Additionally, the strong intervention of the habitat for almost a century also influenced the availability of food for this species.

The birds representing the last individuals are believed to have been killed on the islet off the coast Ile d'Ambre in 1662.

Front view of the skull of Raphus cucullatus By Emőke Dénes

Habitat and distribution

The dodo Raphus cucullatus is an endemic species to the island of Mauritius. This island is located in the southwest of the Indian Ocean, approximately 900 km off the eastern coast of Madagascar.

The habitat of this species consisted of dry forests and lowland rainforests. According to some authors, it is possible that they also occupied areas of high hills where they established mutualistic relationships with the Sideroxylon grandiflorum tree.

The ecoregion to which the habitat of the extinct dodos belongs is known as the jungle of the Mascarene Islands in the Afrotropical eco-zone.

The island has a marked climatic seasonality. Although the native vegetation has been remarkably modified in the most populated regions, the island of Mauritius has a great availability of palms and trees that bear fruit during winter.

Nutrition

Descriptions by ancient explorers indicated that the dodos fed on a large number of seeds, including endemic palm plants such as Latania sp., Dictyosperma sp., Hyophorbe sp. and large trees in the forest. Among these fruits was possibly the aforementioned "dodo tree", Sideroxylon grandiflorum.

These fruits are large, about 5 centimeters in diameter, with a thin exocarp, a fleshy mesocarp, and a strong endocarp.

The presence of large rocks in the dodo's gizzard, which was highly developed, indicates a diet based on items with a certain mechanical resistance to digestion. The diet can also be deduced from the size and strength of the beak, which was capable of splitting very hard seeds.

One of the strongest evidence of the dodo's feeding from fruits of the tambalacoque tree is the discovery of seeds, along with skeletal remains of these animals.

On the other hand, there are currently no species that can fully consume this type of fruit and process the seeds so that they germinate. There are only species that feed on the fleshy part of the fruit, such as the Mauritian parakeet and the flying fox.

Reproduction

These birds presented an evident sexual dimorphism, being the males more developed than the females. It is probable that the dodo reproduced around the month of August due to the climatic characteristics of the island of Mauritius and that during this time a large part of the island's plants produced their fruits.

In this way, dodo chicks could grow rapidly to meet the necessary conditions to survive the cyclone season and the southern summer. Accelerated chick growth was demonstrated because there is a wide variety of bones that show rapid deposition of calcium.

After this period, evidence has been collected that the adults were going through a molting phase of their plumage. The latter coincides with many historical accounts and writings of the sailors of the time.

The dodo bird had clutches made up of a single large egg. It is probable that this species retained some juvenile characters in the adult stage.

Knowing this, the dodo is considered one of the few known cases of pedomorphic birds. Some retained juvenile characters are pectoral underdevelopment and relatively juvenile plumage.

After the first stage of accelerated growth was overcome, it took several years for juvenile individuals to fully mature to adulthood as a result of severe environmental fluctuations and changes in resource availability.

Behavior

Plant-animal relationship

According to some evidence, the dodo bird had a symbiotic relationship with a species of tree commonly known as tambalacoque (Sideroxylon grandiflorum) which belongs to the Sapotaceae family and is also typical of the island of Mauritius.

After the disappearance of the dodo, the tambalacoque suffered a population decline that is hypothetically attributed to the disappearance of the dodo bird.

Apparently, the dodo was an active disperser of the seeds of this species, which is also highly exploited for the value of the wood locally. The passage of the seeds through the digestive tract of these flightless birds greatly facilitated the germination of the latter.

The thick endocarp of the seeds has a great mechanical resistance to the expansion of the embryo inside. After the abrasive and scarifying action of the seeds on the dodo's gizzard, these could germinate more quickly.

The relationship of these plants to the dodo has in part been attributed to the poor germination of this plant in nature. Besides this, there are few trees that are apparently more than 300 years old. However, this hypothesis has not been fully tested.

Nutritional stress

It is likely that during the time of high availability of resources, these species stored fat in order to survive the months of nutritional scarcity.

Some accounts by sailors indicate that the dodos suffered from nutritional stress. This was observable through drastic changes in the body mass of the individuals between November and March.

Courtship and territoriality

It is likely that the males of these large birds made some kind of exhibition during the reproductive season to attract the females. However, this behavior is subject to strong speculation. There are no detailed descriptions of these aspects for this species.

Nor is it known if there were clashes between males for the right to mate.

In addition, due to their large size, they probably behaved like territorial birds, since competition for resources in times of scarcity had to be strong.

References

1. Angst, D., Chinsamy, A., Steel, L., & Hume, JP (2017). Bone histology sheds new light on the ecology of the dodo (Raphus cucullatus, Aves, Columbiformes). Scientific reports, 7 (1), 7993.
2. BirdLife International 2016. Raphus cucullatus. The IUCN Red List of Threatened Species 2016: e.T22690059A93259513. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22690059A93259513.en. Downloaded on 21 December 2019.
3. BirdLife International (2019) Species factsheet: Raphus cucullatus. Downloaded from http://www.birdlife.org on 12/21/2019.
4. Cheke, AS (2006). Establishing extinction dates – the curious case of the Dodo Raphus cucullatus and the Red Hen Aphanapteryx bonasia. Ibis, 148 (1), 155-158.
5. Livezey, BC (1993). An ecomorphological review of the dodo (Raphus cucullatus) and solitaire (Pezophaps solitaria), flightless Columbiformes of the Mascarene Islands. Journal of Zoology, 230 (2), 247-292.
6. Temple, SA (1977). Plant-animal mutualism: coevolution with dodo leads to near extinction of plant. Science, 197 (4306), 885-886.
7. Roberts, DL, & Solow, AR (2003). Flightless birds: when did the dodo become extinct ?. Nature, 426 (6964), 245.
8. Shapiro, B., Sibthorpe, D., Rambaut, A., Austin, J., Wragg, GM, Bininda-Emonds, OR,… & Cooper, A. (2002). Flight of the dodo. Science, 295 (5560), 1683-1683.