The genus Semnopithecus in south India is represented by the Nilgiri langur (S. johnii) and the common Hanuman langur (S. priam thersites). The Nilgiri langur is an endemic to the Western Ghats and is a threatened species while the status of the common langur, an endemic to the Indian-subcontinent, is not known due to deficient data. The lack of knowledge of their distribution, ecology and status makes it difficult for informed conservation initiatives.

These closely related langur species have been reported to hybridise in regions where their ranges adjoin i.e. regions where they are parapatric. The mechanism by which such parapatry is maintained is of considerable importance in understanding the evolution and speciation of the genus. A comparative study of their distribution and ecology is imperative for elucidating these mechanisms.