There are three tahrs, the Arabian Tahr, the Himilayan Tahr, and the Nilgiri Tahr; of which the Nilgiri is the largest. With an average life span of 3 years the species was almost extinct in the late 19th century and has been brought back from the brink to an estimated count of over 2000 individuals. The horns curve towards the animals back. The inside of the horn surface is almost flat, while the back and outside are rounded. They contain growth rings that develop annually, which reveals a tahr's age. Fortunately, Nilgiri tahrs breed very well in captivity, which helps increase their numbers. In the wild, they can breed up to twice in one year, and usually have one offspring at a time. Although twins do occur, it is scarce. Because the Nilgiri Tahr live on steep rocky cliffs, they have gotten the nickname Varai Aadu, which translates to cliff goat. Despite it being considered a tahr, it is more closely related to the sheep than either the Himilayan or Arabian Tahr and domestic livestock remain their competitors for food.