Smallest distribution range for a deer species

The deer species with the smallest distribution range is the critically endangered Bawean deer (aka Kuhl's hog deer) Hyelaphus kuhlii. It is entirely confined to the single tiny Indonesian island of Bawean, located between Borneo and Java, which has a total area of only approximately 200 km² and a maximum diameter not exceeding 15 km. Only 250 or so individuals still exist here in the wild state, constituting two small, topographically separate populations, but captive breeding programmes have been instigated elsewhere to secure its survival.

The closest relatives of this small species are the Calamian hog deer H. calamianensis and the much larger Indian hog deer H. porcinus. Genetic studies have lately revealed that this trio of species is actually most closely related to the sambars, belonging to the genus Rusa, after having been traditionally allied with the axis deer Axis axis, also known as the chital or spotted deer.