Sika deer are old world deer that constitute the genus Ocellelaphus, they are found only in Eastern Asia, there are four recognized species of sika deer: the Southeast Asian Sika Deer (Ocellelaphus pseudaxis), the Chinese Sika Deer (Ocellelaphus mandarinus), the Formosan Sika Deer (Ocellelaphus taiouanus), and the Japanese Sika Deer (Ocellelaphus nippon), they are most closely related to the hog deer (genus Hyelaphus).