Geochelone sulcata
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Family: Testudinidae
Genus: Geochelone
Species: Geochelone sulcata
G.sulcata is one of the largest existing species of land tortoises, with males measuring up to 75-90 cm in length and weighing up to 100 kg, while females are smaller. Native to sub-Saharan Africa, in adults the scutes of the carapace are of a light shade at the centre and darker on the outside; the plastron is ivory coloured. The skin is light brown, the limbs are stocky and robust and covered with very pronounced scales; the lower limbs present characteristic and evident horny tubercles. The native habitat of G.sulcata consists of savannahs and shrublands typical of semi-desert and arid environments, where day temperatures are very high, the thermal excursion between day and night is significant, the humidity rate is very low but interspersed with heavy seasonal rainfalls. In addition to the difference in size, sexual dimorphism comprises the concave plastron, the larger size of the tail and the anal scutes of the plastron which form a more obtuse angle in the male than in the female. Being a tropical species, G. sulcata does not go into hibernation, as at its native latitudes temperatures remain more or less constant throughout the year, but it can “aestivate”, i.e. find refuge in burrows dug in the ground to escape the extreme heat: this is not a true hibernation but rather a period of inactivity (Figs. 1, 2 and 3).
The diet of G. sulcata is exclusively vegetarian and must include high-fibre foods and especially calcium, possibly with the addition of supplements especially in younger specimens, so as to meet the nutritional needs resulting from the rapid development of thebony structures which is typical of this chelonian species; the ration should mostly consist of good hay, supplemented with field grasses, clovers and alfalfa, while vegetables and fruit should be cut down to a minimimum and especially the latter, if possible, should be excluded from the diet.
Sexual maturity is reached no earlier than 4-5 years of age and a shell length between 30 and 40 cm. Mating behaviour is rather violent, with the male chasing, ramming and biting the female. The female lays her eggs by excavating a nest of at least twenty centimeters in depth, selecting a location which is both sheltered and exposed to the sun. The young tortoises will hatch after an extremely variable incubation period, which ranges between 2.5 and 5 months, at temperatures between 28-31°C. The average egg size is 4 cm and up to 20-25 eggs can be laid at a time, for a total of 4-5 clutches per year.
The considerable size reached by this reptile may represent a management and housing challenge, as the terrarium is a viable solution only in the first years of life, when the size of young tortoises is still relatively small. Adults require plenty of space and it is therefore easier to fence-off an area within a room than to use a real terrarium. The temperature gradient of the enclosure should fluctuate between 20 and 35°C, in order to allow the reptile to thermoregulate itself. More than one source of UVB light should be made available next to the heating lamps, and humidity must be kept rather low, under 60%. A shelter or burrow of sufficient size must always be available and sand, soil, hay or straw can be used as substrate. During the cold season the specimens must necessarily be kept indoors, while during the summer they should preferably be kept outdoors, providing them with shelters and shaded areas. A water dish must always be available.
Geochelone sulcata is included in theCITES Appendix II and in Annex B to Regulation (EC) No 1332/2005.