African spurred tortoise

The African spurred tortoise (Centrochelys sulcata), also called the sulcata tortoise, is an endangered species of tortoise inhabiting the southern edge of the Sahara Desert and the Sahel. It is the largest mainland species of tortoise in Africa, and the third-largest in the world, after the Galapagos tortoise and Aldabra giant tortoise. It is the only living species in its genus, Centrochelys.

In 1779 the English illustrator John Frederick Miller included a hand-coloured plate of the African spurred tortoise in his Icones animalium et plantarum and coined the binomial name Testudo sulcata. Its specific name sulcata is from the Latin word sulcus meaning "furrow" and refers to the furrows on the tortoise's scales. The species was subsequently given other binomial names. There are no recognized subspecies despite there being two separate populations, one in Western Africa and the other in Eastern Africa. There are also three different, yet similar, haplotypes. One haplotype is found in and closely around Sudan, another is found in the western portion of their range, and the last haplotype is found in Senegal, Mali, and Sudan.

The African spurred tortoise is native to the Sahara Desert and the Sahel, a transitional ecoregion of semiarid grasslands, savannas, and thorn shrublands found in the countries of Burkina Faso, the Central African Republic, Chad, Eritrea, Ethiopia, Mali, Mauritania, Nigeria, Senegal, Saudi Arabia, Sudan, Yemen and possibly in Somalia, Algeria, Benin, and Cameroon. It is possibly extirpated from Djibouti and Togo. They are found on hills, stable dunes, and flat areas with shrubs and high grass. They also like to settle in areas with interrupted streams or rivers. In these arid regions, the tortoise excavates burrows in the ground to get to areas with higher moisture levels, and spends the hottest part of the day in these burrows. This is known as aestivation. In the wild, they may burrow very deep, up to 15 m deep and 30 m long. Plants such as grasses and succulents grow around their burrows if kept moist, and in nature they continue to grow for the tortoise to eat if the soil is replenished with its feces. Sulcata tortoises found in the Sudanese part of their range may reach significantly greater size at maturity than those found in other regions.

C. sulcata is the largest species of tortoise in Africa and is also third-largest species of tortoise in the world. The species is the largest of the mainland tortoises. Males have an average mass of about 81 kg, but some males have been recorded at over 100 kg, with one weighing more than 120 kg. They have a straight carapace length of around 86.0 cm in males. Females have a straight carapace length of about 57.8 cm. Males of a curved carapace length of about 101.0 cm and females have approximately 67.0 cm of curved carapace length. Despite being the largest tortoise in Africa, hatchlings measure merely about 44 millimeters and weigh around 40 grams. They grow very quickly, reaching 6–10 in (15–25 cm) within the first few years of their lives. The tortoises grow faster when there is more rainfall and slower when there is less. They reach sexual maturity after 10 to 15 years. In captivity their life span is around 54 years. In the wild their lifespan is unknown but is believed to exceed 75 years. The tortoise has no known predators when they are hatchlings or adults. In fact it is believed that they are nearly immune to predators when their weight exceeds 30 kg. On the other hand tortoise eggs are sought after by many predators such as numerous species of lizards and potentially mongooses. In the wild the leading cause of death is being unable to right themselves after they have been flipped onto their backs, chiefly as a result of fighting between adult males.

Sulcata tortoises are mostly herbivores. Primarily, their diets consist of many types of grasses, plants (especially succulent plants), and hay. Their overall diet should be high in fiber and very low in protein. Too much protein will lead to the tortoise growing too fast, which can result in metabolic bone disease, a condition that is characterized by distortion of the skeleton and weakened bone structure and can lead to lameness, lower quality of life, and/or shortened lifespan. Flowers and other plants including cactus pads can be consumed. In the wild, they have been observed to also eat plants and algae off the surface of the water. African spurred tortoises are also capable of eating various vegetables such as endive, dandelion greens, and dark leafy greens. Despite being herbivores, they will occasionally eat the carcasses of dead animals. They mostly eat dead goats and zebras that have been pushed downstream during the wet season on the rivers and streams next to which tortoises settle. If a human settlement is nearby they will also feed on refuse.

Copulation takes place right after the rainy season, during the months from September through November with breeding actions occur in the morning. Male C. sulcata are extremely territorial. Males combat each other for breeding rights with the females and are vocal during copulation. Larger males tend to always win sexual combat.

Sixty days after mating, the female begins to roam looking for suitable nesting sites. For five to 15 days, four or five nests may be excavated before she selects the perfect location in which the eggs will be laid. Females tend to lay around two to three clutches of eggs with each clutch containing 14 to 40 eggs.

Loose soil is kicked out of the depression, and the female may frequently urinate into the depression. Once it reaches about 2 feet (60 cm) in diameter and 3–6 in (7–14 cm) deep, a further depression, measuring some 8 in (20 cm) across and in depth, will be dug out towards the back of the original depression. The work of digging the nest may take up to five hours; the speed with which it is dug seems to be dependent upon the relative hardness of the ground. It usually takes place when the ambient air temperature is at least 78 °F (27 °C). Once the nest is dug, the female begins to lay an egg every three minutes. Clutches may contain 15–30 or more eggs. After the eggs are laid, the female fills in the nest, taking an hour or more to fully cover them all. Incubation should be 86 to 88 °F, and will take from 90 to 120 days.