Muntjac seasonal rut, and mating can take place at any time of year; this behaviour is retained by populations introduced to temperate countries. Males have short antlers, which can regrow, but they tend to fight for territory with their "tusks" (downward-pointing canine teeth). The presence of these "tusks" is otherwise unknown in native British wild deer and can be discriminatory when trying to differentiate a muntjac from an immature native deer, although water deer also have visible tusks; however, they are much less widespread. Muntjac are of great interest in evolutionary studies because of their dramatic chromosome variations and the recent
Reeves's muntjac species except where already established. Colonies exist throughout England south of Derbyshire, and the population continues to grow. In Ireland, sightings in 2008 caused the government, concerned at the risk of the species becoming established, to quickly introduce a year-round hunting season. In the 1960s, several specimens escaped from an exhibition zoo in the Bōsō Peninsula in eastern Japan. By 2017, their numbers had reached at least 60,000. It is considered a harmful invasive species and has inflicted severe damage to ashitaba plantations. Also, Reeves's muntjac escaped a zoo on Izu Ōshima in 1970 when a fence fell due to