in gregarious deer; consequently, this deer's coat is little differentiated. Young are born dark brown with white stripes and spots along their upper torso. Teeth The water deer have developed long canine teeth which protrude from the upper jaw like the canines of musk deer. The canines are fairly large in the bucks, ranging in length from on average to as long as . Does, in comparison, have tiny canines that are an average of in length. The teeth usually erupt in the autumn of the deer's first year at approximately 6–7 months of age. By early spring, the recently erupted tusks reach approximately 50% of their final length. As the tusks develop, the root remains open until the deer is about eighteen months to two years old. When fully grown, only about 60% of the tusk is visible below the gum. These canines are held loosely in their sockets, with their movements controlled by facial muscles. The buck can draw them backwards out of the way when eating. In aggressive encounters, he thrusts his canines out and draws in his lower lip to pull his teeth closer together. He then presents an impressive two-pronged weapon to rival males. It is due to these teeth that this animal is often referred to as a "vampire deer". Genetic diversity The mitochondrial DNA of samples from the native Chinese population and the introduced UK population was analysed to infer each population's genetic structure and genetic diversity. It was found that the UK population displays lower levels of genetic diversity, and that there is genetic differentiation between the native and introduced population. It was also found that the source population of the British deer is likely to be extinct. This has implications for the conservation of the different populations, especially as Hydropotes inermis is classified as Vulnerable in its native range according to the IUCN Red List. Behaviour Apart from mating during the rutting season, water deer are solitary animals, and males are highly territorial. Each buck marks out his territory with urine and feces. Sometimes a small pit is dug and it is possible that in digging, the male releases scent from the interdigital glands on its feet. The male also scent-marks by holding a thin tree in his mouth behind the upper canines and rubbing his preorbital glands against it. Males may also bite off vegetation to delineate territorial boundaries. Water