Ten subspecies of mule deer have been identified including two black-tailed deer subspecies and a hybrid subspecies of the mule deer and the white-tailed deer (Odocoileus virginianus).
Ten subspecies of the mule deer have been identified, two of which, (O. h. columbianus and O. h. sitkensis,) are classified as black-tailed deer. The black-tailed deer was at one time treated as a separate species, but is now mostly recognized as conspecific with the mule deer.
Subspecies of the mule deer include the California mule deer (O. h. californicus), Cedros Island deer (O. h. cerrosensis), Columbian black-tailed deer (O. h. columbianus), desert mule deer (O. h. eremicus), southern mule deer (O. h. fuliginatus), Rocky Mountain mule deer (O. h. hemionus), Inyo mule deer (O. h. inyoensis), peninusla mule deer (O. h. peninsulae), Tiburon Island mule deer (O. h. sheldoni), and Sitka black-tailed deer (O. h. sitkensis).
The validity of the Inyo mule deer (O. h. inyoensis) is questionable.
The desert mule deer, also known as the burro mule deer, is sometimes referred to as O. h. crooki, but O. h. eremicus is considered the correct name. The specimen type of this subspecies is a hybrid of the mule deer and the white-tailed deer (Odocoileus virginianus).
Although most of the mule deer’s subspecies are not threatened, the Cedros Island subspecies (O. h. cerrocensis) is considered to be Vulnerable on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, as of 1988. This subspecies is in danger of becoming extinct because its densities are very low on the island where it occurs and poaching and predation by feral dogs are high.