|
The Cold Blooded NewsThe Newsletter of the Colorado Herpetological SocietyVolume 28, Number 10; October, 2001 |
This is a very interesting chelonian! Perhaps more than other tortoise species, it is exposed to very extreme conditions in its native lands.
Description and Identification:
The Central Asian tortoise is not a large tortoise. The carapace is rounded, and almost as broad as it is long. The straight carapace length (SCL) can reach a maximum of 22 cm. Although such lengths are relatively rare, there is a report of a specimen in a Russian museum that measured 28.6 cm SGL. A 16 cm SCL is quite respectable size for this tortoise. There are eleven marginals. and the supra-caudal is undivided. The plastron is relatively flat and lacks a movable hinge. The centre fusion on the plastron can be somewhat elevated, resulting in a ridge. Also, the males have a very slight concavity of the posterior portion of the plastron, which is so slight that it can be difficult to spot. Sexual dimorphism does become more prominent, however, when the tail is examined. The tail of a male Central Asian tortoise is much larger. In fact, a male that is one third the size of a female can have a tail as big as she does. Females of this species tend to be larger than males. The tortoise's hind legs are elephant-like. and the front ones are heavily armored, with prominent scalation. These scales, when the head is withdrawn, help form a barrier as the legs protect the head in this position - the result being that the head of the tortoise is completely hidden inside the shell. One of the key features which distinguish the Central Asian tortoise from other Testudo tortoises is the fact that both the front and the hind legs have four toes: the other members of the genus having five on the front feet.
The colour of the head and limbs is a yellowish- brown to brown. The neck, especially in younger specimens, tends to be lighter (more yellowish) in colour. The shell has dark brown to charcoal areolae, with the margins of the scutes a yellowish tan to greenish colour. It is fascinating to note that faster growth results in a lighter coloured tortoise! A wild specimen that may take twenty or more years to grow to a good size will be darker than a captive that took maybe ten years to grow to the same size. The plastron is of darker colouration than the carapace.
Perhaps the two most similar tortoises to the Central Asian tortoise are Testudo hermanni, Hermann's tortoise, and T. graeca, the Greek tortoise. The Central Asian tortoise is really quite distinct in appearance from these other species, being rounder, flatter of carapace, and more "solid" in appearance, but for those who require more specifics, here they are: Herman's tortoise differs from the Central Asian tortoise mainly in that the supracaudal marginal scute is divided. It also has five toes on its front.
Diet:
Like many other tortoises, the Central Asian tortoise in the wild has a high fiber, low protein diet. Due to their short yearly activity period, this species eats "almost anything" they come across when they are active. Since grasses are the most common edible things in their harsh habitat, this is their staple diet.
This tortoise also eats some non-vegetable items such as carrion, and may even include some of the bones in their repast. To increase digestive efficiency, these tortoises are coprophagous; that is, they engage in the enchanting habit of eating their own and other animals' dung! This rugged diet illustrates the lengths a wild creature must go to in order to survive in a harsh environment.
Behavior and Ecology:
The most notable aspect of the behavior of the Central Asian tortoise is their overall lack of activity. These tortoises are inactive most of the year, and are one of the only reptiles known to both hibernate during the winter and aestivate during the summer. This, again, is an adaptation to an environment, which experiences frigid winters and scorching summers. For example, in the area of Kabul, Afghanistan, tortoises experience temperatures as low as -10 degrees Celsius in January, and highs of 33 degrees Celsius in July. This temperature range is experienced by very few other reptiles (some Canadian parallels being the Bulisnakes and Eastern short-horned lizards of Alberta). In between aestivation and hibernation these tortoises are active as little as three months a year! This time period usually falls from March through to May. During this time, the Central Asian tortoise must mate, lay eggs, and eat enough to survive the next period of inactivity.
Central Asian tortoises are very proficient diggers. They willingly dig in any kind of soil conditions, including very hard-packed substrates. What enables them to do this is their stubborn attitude and extremely powerful front legs! These legs are more powerful than those of related tortoise species. Burrows of this tortoise can be as much as two metres deep. This deep burrow protects the tortoise from extreme heat or extreme cold, depending on the season. Burrows are usually dug on the eastern or southeastern side of a slope, thereby being exposed to sunlight in the morning and early afternoon. These tortoises sometimes use abandoned rodent burrows as a start for their own burrows. It has been observed that Central Asian tortoises will visit burrows of other individuals, sometimes with more than one tortoise sleeping in one burrow.
Courting and Reproduction:
The courting and mating behaviors of the Central Asian tortoise are quite complex. Male tortoises of this species will fight at this time. The fight generally entails running at each other and the ramming of shells. The intention behind this behavior is to flip the other male over onto his back. If this happens, the upside-down male can die in the sun if he doesn't manage to turn back over, right side up, quickly. Young males have even been noted to ram other objects when other tortoises are not available; such is their adolescent frustration.
Courting continues when victorious males approach females. The male will circle the female, trying to bite at her head and front legs. She, understandably, resists this by pivoting away from him. The neck of the male is fully extended at this time, and he will bob his head in a vertical fashion at the female. The male will then attempt to mount the female. If she is unreceptive, or doesn't like him, she will either walk away, or push the back edge of her carapace into the ground, making mating impossible for the male. An unreceptive female can be as dangerous as a rival male, as she tends to be bigger and can also flip the male on his back. Copulation is again accompanied by a full extension of the male's neck and by high-pitched vocalizations.
Mating is reported to commence in March, almost immediately after activity starts, and continues to June in some areas of the Central Asian tortoise's range. In other areas this window of activity is shorter, lasting only until May. Laying of eggs begins soon, almost after mating finishes. A typical clutch consists of two to four oval eggs, two or three clutches per season not being uncommon. Egg sizes vary slightly, but are about 42 mm by 30 mm. Egg weight averages twenty-two to twenty-five grams at laying.
Eggs of this tortoise incubated at 30 to 31 degrees Celsius at about 80% humidity hatch after 61 to 75 days on average. It should be noted that these values are from data gathered from captive breeding. In the wild, it is unlikely that eggs are at constant humidity and temperature during the incubation. In fact, in the dry, almost desert-like habitats that these tortoises inhabit, the night-time lows in May can be as much as fifteen degrees lower than the day-time highs! Even in a burrow exhibiting more constant conditions, there is bound to be some temperature fluctuation.
On hatching, neonate Central Asian tortoises measure 42 to 50 mm SCL. and weigh between 18 and 24 grams. The young have a more yellow colouration than the adults. Their legs are also relatively short, so movement is slow, as they sometimes cannot reach the ground with a leg or two on excessively rough terrain. This is a temporary impediment, however, as growth is rapid, and the problem is soon overcome. In just over a year, baby T. horsfieldi can double their length and quadruple their weight! This tortoise species, it is speculated, reaches sexual maturity in seven to ten years.
A Few Notes on Systematics:
There is great controversy on the phyllogenetic relationship of the Central Asian tortoise to its closest relatives. This species is very closely related to T. hermanni and T. graeca. Nonetheless, in 1966, Khozatsky and Mylnarski suggested mov1ng the Central Asian tortoise out of the genus Testudo and into a monotypic genus: Agrionemys. They noted that this tortoise lacks a hinged plastron, unlike other Testudo tortoises. Also, the claw and metacarpal position is different. Ever since, it seems that western books assign the Latin Testudo horsfieldi to the Central-Asian tortoise, and books from Eastern Bloc countries use Agrionemys horsfieldi. Perhaps now that scientists are less obstructed by the political motives of their countries, they will be able to come to some agreement!
Testudo horsfieldi has one synonym. This is Testudo baluchiorum, (Annadale. 1906). The type locality is in Baluchistan and the holotype is in Calcutta, India.
The Central Asian Tortoise and People:
It is interesting to note that Central Asian tortoises were the first tortoises in space! They orbited the Earth and moon with a bunch of other animals and astronauts in the Soviet interplanetary probe number five in October 1986!
Not all contact between people and these tortoises can be described as glorious, however. Most contact between these two species has been detrimental to the tortoises. Unlike the plights of other reptiles, many of which are victims of habitat corruption and pollution, the largest problem for Testudo horsfieldi populations lies in over-collecting for the pet trade. Between 1965 and 1971, 119,319 specimens of Horsfield's tortoise were imported into the United Kingdom. It is to be remembered that this figure accounts only for one country and only for the recorded specimens! The true figure would surely be even more staggering!
It is alarming to note that one permit alone, issued by the USSR State Committee for Environmental Protection on 28 May 1993 to the Czech Republic, allowed the removal from the wild of 1250 live specimens of Central Asian tortoise! All of these tortoises came from Uzbekistan. This illustrates that the import numbers of this animal are not decreasing, and that many countries will issue export permits for vast quantities of specimens of threatened species: the Central Asian tortoise is listed as CITES Appendix II.
The Central Asian tortoise is a very unique reptile. It endures a very hard life in a harsh habitat. It is a testimony to its resilience that it thrives to this day, despite the over-collecting of the past thirty years. Hopefully, this strange animal will continue to thrive well into the twenty-first century. Testudo horsfieldi is definitely worth further study, with much yet to be learned about it.
|
Next Article: Researchers Throw a Curve into Snakes' Mating Game |
|
Return to Cold Blooded News Page |
Return to CHS Home Page |