Turtles 9: New Arrival

Just gone on show in one of the pools in the Reptile House is one of the rarest and most endangered of all turtles, the Roti Island Snake-Necked Turtle, Chelodina mccordi. Originating from an island near New Guinea, it was only split from the more widespread New Guinea Snake-Necked Turtle in 1994. Sadly, collection for the international pet trade for this endemic species has placed it on the Critically Endangered list, and today it is only known from a few sites on the island with a total area of 70km2.

Turtles and Tortoises 7: the (no longer) Egyptian Tortoise

Baby T.kleinemanni

For many years Bristol has had on show one of the world’s smallest tortoises, the Egyptian or Kleineman’s Tortoise Testudo kleinemanni. Despite its’ name, sadly it is no longer found in Egypt itself, and is classed as Critically Endangered in the wild.


Threats to tortoises I have described in previous posts have mainly been from habitat destruction and collection for food. With T.kleinemanni the situation is different, as practically the entire cause of its current dire situation is collection for the pet trade.

Turtles and Tortoises 6: Giant Pond Turtle

Orlitia borneensis

A new addition to Bristol Zoos’ collection of turtles this year is a pair of one of the largest freshwater turtles in the world, the Giant Pond Terrapin Orlitia borneensis. With a shell length of 80cm and a maximum weight of 50kg (or as much as Cheryl Cole as the sign somewhat ungallantly puts it) this species is an impressive sight. As you might guess from the specific name, it is found in Borneo, but its range extends through Sumatra and through peninsula Malaya as well.

Turtles and Tortoises 5: Black Marsh Turtle

The aquatic chelonians I have been discussing so far all belong to a single family, the Geoemydidae. This is the most diverse of all living groups of turtles, with over 70 different species in 23 genera. The centre of distribution of the family is in south east Asia, with outliers in Europe and North Africa (the European Mauremys species), and a separate group in Central and South America (the Neotropical Wood Turtles Rhinoclemmys). Almost all of them are highly aquatic, and even the more terrestrial forms tend to prefer damp habitats. Despite this, they are generally believed to be close to the fully terrestrial tortoises such as the Aldabra Giant Tortoise and its smaller relatives. The age of the group is not clear, but it probably dates back to the late Cretaceous.

Turtles and Tortoises 4: Annam Leaf Turtle

M.annamensis adult

One of the peculiar features of the fauna and flora of Europe is that many of their closest relatives live in eastern Asia, with a vast gap in between with no connecting forms. This is a signal of the geological and climate events that have effected Eurasia, including the uplifting of the Himalaya following the collision of the Indian subcontinent with Asia, and above all the glaciations of the last few million years. In Europe the main mountain chains are aligned east-west, creating roadblocks to the migration of species north and south in response to climate change, whereas in eastern Asia mountain chains tend to be aligned north-south. As a result, while glaciations caused repeated extinctions in Europe, their Asian relatives managed to survive.

Turtles and Tortoises 3: Boxed into a corner

C.amboinensis

One of the most serious conservation issues today is the catastrophic decline in recent years of the various species of turtle to be found in south-east Asia. Turtles have been used for local consumption for many years, but urbanisation (which destroys habitat), agricultural development, pollution, and above all over collection from the wild for the expanding food markets of China has placed all of them on the critical list. Many species are in fact only known from specimens found in food markets, and probably have very restricted ranges if they still survive at all.

Turtles and Tortoises 2: Not just on Galapagos

Female D. dussimieri, Bristol

Today, when the phrase giant tortoise is heard, people immediately think of the giant tortoises of the Galapagos. That group of species however is just the largest surviving group of species in a world which once had giant tortoises almost everywhere, from South America to Southeast Asia. Away from the Galapagos, the largest tortoises alive today are the African Spurred Tortoise, Geochelone sulcata, a mainland species that can grow to 90cm long and a weight of 90kg, and the giant tortoises we have at Bristol, a group of seven Aldabra Giant Tortoises Dipsochelys dussumieri.

Turtles and Tortoises 1: The Pancake Tortoise

This series of posts will be about one of the most famous groups of reptiles, the chelonians, variously referred to as turtles, tortoises or terrapins. Although they are subdivided into various taxonomic groups, these do not actually correlate with the various English names. In American English, they are almost all referred to as turtles. In British English, the names differ by habitat – tortoise is used to refer to terrestrial animals, turtle to marine forms, and terrapin to freshwater animals. Why we have so many names is unclear, as there are currently no breeding populations of any chelonian native to Britain. Any terrapins seen in the UK are invariably released pets, usually Trachemys scripta, the Red-eared Terrapin. In the past the European Pond Terrapin, Emys orbicularis, was resident in the UK but became extinct as a result of a change to a colder climate many thousands of years ago.

Land of the Dodo 5: Tortoises then and now

At the time of discovery, the Mascarenes were home to five species of giant tortoise. Mauritius and Rodrigues each had two, a saddle backed form adapted for browsing at higher levels and a smaller (c 12kg) domed form better shaped for grazing (most the others were probably in the 60-100 kg range). Reunion only had a single species, which was domed but considerably larger than the forms on the other islands. A painting by Julian Hume, who has done several paintings of Mascarene wildlife, is shown at the top of this post.
The various forms have all been placed in the endemic genus Cylindraspis, although they were formerly all placed in the widespread genus Geochelone, along with the Galapagos and many African tortoises. These have now all been split into separate genera. The closest living relative is probably the Madagascan Radiated tortoise Astrochelys radiata, which is about the size of the smallest domed form, the Rodrigues C.peltastes. (image from Cites website). Derived from the same ancestor is the Aldabra Giant Tortoise, Dipsochelys gigantea, which used to occur throughout the Seychelles.

The genus apparently first evolved on Mauritius, later spreading to Rodrigues and Reunion. One interesting feature is that their shells were extremely thin, as protection was not needed on the pristine islands from mammalian predators. As hatchlings, tortoises would have been preyed on by native birds, especially the endemic night heron, and land crabs would probably have also taken some.

The giant tortoises were the dominant herbivores on the island. Their grazing would have kept areas of grassland open, and their browsing strongly influenced the larger vegetation. Many Mascarene plants have vividly coloured juvenile foliage, designed to discourage browsing until the plants grow too tall to be eaten by tortoises, and many trees produce flowers and fruit at the base of the trunks, where tortoises could distribute the seeds.

The extinction of the tortoises was almost certainly caused by direct hunting pressure from humans. Vast numbers were taken from all the islands as a source of fresh meat on sailing voyages, and they were even killed for extraction of oil. The coup de grace was probably given by pigs (which ate eggs) and cats (which ate hatchlings).

What is especially tragic is that at least one species nearly made it. In 1844, a group of visitors on a scientific expedition to Round Island discovered survivors, and one member of the party “captured a female land tortoise in one of the caves on Round Island and brought it to Mauritius, where it produced numerous progeny, which distributed among his acquaintance”. Given the lifespan of giant tortoises, a hatchling in 1845 could even have lived to the present day.

Today, giant tortoises can once more be found living in at least semi-wild conditions on Mauritius. As part of the environmental reconstruction programme, Aldabra Giant Tortoises were released on Isle Aux Aigrettes, and have successfully bred in the wild. The effect on the vegetation has been highly beneficial, and plans are in development for their use on other offshore islands, possibly in conjunction with Radiated Tortoises.

At Bristol Zoo we have four Aldabra Tortoises, an adult male called Biggy who is at least 80 years old, and three females of which two are old enough to breed, although they have not so far shown signs of doing so. The latest arrival, “Matilda” , who at about 15 years is the smallest, is in the picture below.