Tortoises, Terrapins and Turtles



Dave Rushworth


Probably the most well known and least understood of all our animals are the TORTOISES. Referred to, flippantly, as ?mobile meat pies? or, further south as ?karroo-kreel? and the subject of many an indigenous ?skildpadbraai?, most members of the Order CHELONIA are threatened in South Africa. The species most encountered in this part of the country are the leopard tortoise, a couple of the hinged tortoises and the cape and serrated Terrapins.

Members of this Order are called by various names throughout the world but in South Africa the name TORTOISE is used to refer to the true LAND TORTOISES - (Family Testudinidae). The name TERRAPIN is used to refer to the FRESHWATER TORTOISES - (Family Pelomedusidae), and the name TURTLE is used to refer to MARINE TORTOISES of the Families - Cheloniidae and Dermochelyidae.

All South African species are classified under the Suborder Cryptodira (hiddennecked tortoises) EXCEPT the terrapins, which fold their necks in sideways, which are classified in the Suborder Pleurodira. Both of these Suborders fall under the Order Chelonia, which is one of the FOUR Orders of the Class Reptilia - the other three being - Crocodilia (Crocodiles) - Squamata (lizards and snakes) and Rhynchocephalia (Tuatara - of New Zealand). The whole Order is very old and the crocodiles and tortoises are presumed to have been in existence long before the DINOSAURS.

Statistics And Distribution

South Africa, and in particular the Cape, has the richest diversity of tortoises in the world. Of the 40 species of tortoise known, South Africa has 12 species and 2 Subspecies. In addition, the southern African region has 5 terrapin and 5 turtle species. These include the smallest tortoise (Homopus signatus signatus - Namaqualand speckled padloper), one of the rarest tortoises (Psammobates geometricus - Geometric tortoise) and the largest turtle (Dermochelys coriacea - leatherback turtle) in the world.

Of the terrapins the cape terrapin is the most common while the serrated terrapin is found in the northern and eastern regions. The other three terrapins occur mainly in Mocambique but have been recorded along the eastern border of South Africa. The turtles of the family Cheloniidae all have bony shells covered with a layer of horny scales. These, the loggerhead, green, hawksbill and olive ridley turtles are found along the south eastern coasts. The leatherback turtle (of the Family Dermochelyidae), which has a bony shell covered with a leathery layer of skin, is found right round the southern African coast line.

Of the tortoises, the leopard tortoise is the most wide spread throughout South Africa, excluding some of the highveld. The serrated tortoise is wide spread in the Kalahari sand area and the savannah hinged tortoise occurs in most of the northern areas of the country. All other species are fairly restricted in their distribution, mainly in the Cape. For further detailed information on these interesting creatures I suggest reading - The South African Tortoise Book by Richard Boycott and Ortwin Bourquin - to whom I am grateful for statistics and distribution quoted.

Adaptations

The bony, convex, upper section of the shell is the ?carapace? and the flat, lower part of the shell is called the ?plastron?. The shells of the various species may vary with age and wear from a plain grey / brown to quite brightly marked with cream and black patterns, depending on the species. The growth rings on the scales, if visible, can be used as an indicator of age but do not always correlate to annual growth. Males have longer tails than females and in some species the anal scales are shaped so that the female has a rounded opening to accommodate the laying of eggs while the males have a ?V? shaped opening.

In the leopard tortoise female the carapace is broader and usually less domed than that of a male and the plastron may be concave while that of the female may be slightly convex. Males are normally smaller than females of the same age. Growth rate depends on various conditions, mainly temperature and food intake, like many other reptiles. All the Chelonia have powerful, horny ?beaks?, with sharp cutting edges, with which they gather food.

Lacking teeth, they chew food to a suitable size for swallowing, helped down by a blunt ?tongue?, Although they have been noted ?sniffing? at food and often make ?choices?, they do not appear to have the subtle tasting ability of other animals and will often eat bitter items unpalatable to other species. Tortoises, which have blunt claws, are generally herbivorous, but are known to eat snails, millipedes and certain invertebrates.

The latter, in addition to bone-chewing and egg shells, are apparently taken for their calcium content. Terrapins, which have quite sharp claws, are generally carnivorous and feed on water animals and mammal carcasses. Turtles, which have clawless, paddle-like flippers, are normally carnivorous when young, becoming more specialised when mature. The ?hinged tortoises? are able to close the back section of the carapace for protection, while the hinged terrapins close the front section of the plastron.

Tortoises pull their heads straight back into the shell and gain further protection from the armoured scales of the withdrawn front legs. Terrapins tuck their heads in sideways and withdraw the front legs before closing the hinged section. Cape terrapins just pull the head in sideways and use the protection of the clawed, front feet. They can use their powerful bite to good effect. In terrapins, the eyes and nostrils are situated far forward on the head so that they can breathe and see while the rest of their body remains submerged.?Terrapins also have ?stink glands? from which they can emit a foul smelling fluid to repel predators.

Threats To Survival

The Chelonia, like most other reptiles and birds, probably have about a 2% survival rate to adulthood, after predation and other casualties. Depending on the species, they lay from 10 to more than 100 eggs which are buried in sand or soil. Some take over a year to hatch. During this time they are vulnerable to many digging predators such as mongooses and monitor lizards, flooding and temperature. Those young that hatch successfully are subject to heavy predation from many sources. Few survive to become breeding adults.

As adults they are coming under increasing threat from human activities. Many of our tortoise species have very specific habitat requirements. They are unable to live in other areas because of the lack of specific food or competition from other species. Destruction of habitat for agriculture is a major threat to their survival, particularly in the Cape. Large numbers are still killed as a traditional source of food and the ?pet trade? encourages the capture of numbers, far in excess of their reproduction.

The largest tortoise species have all been exterminated apart from on the islands of Galapagos and Aldabra and certain species in the Cape are going the same way. Wild fires are an extreme threat to slow moving tortoises. While they may survive a cold burn with slight scorching, a hot fire will certainly kill them in great numbers. Very low ?hot wires? on electric fences are responsible for the deaths of many of these creatures.

Badly constructed roads with high earth banks become a real barrier to their movement and sharp, concrete curbs on paved roads are a real trap. The tortoises are unable to escape from the road verges and literally fry to death on the hot road surfaces, unless they are run over by fast moving traffic.

Conservation Measures

All tortoises are protected by law in South Africa and may not be killed, captured or kept in captivity. The only reason to pick one up would be to remove it to a place of safety from a position where it was unlikely to survive - e.g. - a busy road or from the threat of an approaching fire. If picked up the animal should be released as near as possible to the place it was located. In the Cape, especially, where species distribution is limited by habitat, untold harm will be done by releasing the captured animal into the distribution area of another species or where it may not have the correct food plants.

Ensure that bottom wires on fences are high enough to allow the passage of small animals. Construct escape routes on roads, ditches and waterholes. Burn only using the correct method and at the right time when vulnerable animals are likely to be dormant. Tortoises are able to survive in very dry conditions by storing water obtained from succulent plants although they will drink water readily when it is available. They store water in a cloacal bursa or sack in the rear of the body for use when required.

They will also excrete this water supply as a defence against predators and to dampen dry soil when digging holes in which to lay eggs. If you pick up a tortoise trying to survive in very dry conditions it may excrete its valuable water supply, resulting in the eventual death of the animal. The same applies to the disturbance of any frog or other animal trying to conserve their supply of moisture during the dry periods.

?Leave them alone and undisturbed unless absolutely necessary - and then only very carefully to prevent them opening up their limbs or expelling their fluids. A little bit of thought and care for other species will go a long way to assisting their survival. Take a trip to the nearby Reptile Park to learn more about these fascinating animals. Think before you carry out any action - and - ?Do unto others as you would have them do unto you.?



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