This species prefers woodlands and forest with dense understorey, but forages in open grassy areas (Smith and Xie 2008). The main diet includes grass, some browse, and even fruit. The species is crepuscular, but sometimes active by day and night, and forages singly or in small herds, with dominant males with harems. Herds migrate to lower valleys in winter. Adults can live up to 25 years. Typically, mating occurs in autumn and gestation is about 210-223 days with young being born in April and May.

In Tiebu Nature Reserve, Sichuan, Sika were reported to forage preferentially in small patches of subalpine shrub and subalpine brush mixed with forest (Guo 2002). Sika fed on a wide variety of plant species in Teibu. In Viet Nam, diet of C. n. pseudaxis was reported to included browse and fruits (Dang Huy Huynh, Tran Van Duc, and Hoang Minh Khien pers. comm.). In Taiwan, C. n. taiouanus inhabited open forests and grasslands of valley bottoms and foothills below 300 m (McCullough 1974, Horng-jye Su undated). C. n. mandarinus and C. n. grassianus probably occurred in upland forests (IUCN 1972). C. n. keramae favours lowland forests and plains (WWF 1984). In Viet Nam, C. n. pseudaxis group size was 5-30 animals (Dang Huy Huynh, Tran Van Duc, and Hoang Minh Khien pers. comm.). In China, C. e. sichuanicus forms large aggregations during May-August (Sheng Helin and Zhang Endi pers. comm.). In Viet Nam, C. n. pseudaxis was thought to be primarily sedentary, although some seasonal movement took place depending on water availability (Dang Huy Huynh, Tran Van Duc and Hoang Minh Khien pers. comm.). In China, rut occurs during September-November. Fawning occurs in May-July following a 210-213 day gestation. Single fawns are the rule, but twins are sometimes observed among prime-aged females (Guo and Zheng 2005). Sexual maturity is reached at 1.5 years (Sheng and Ohtaishi 1993).

The Sika was distributed across east Asia, from central China in the west to Japan and Korea in the east, and from the extreme eastern tip of Russia in the north to southern China and Viet Nam. Specifically, it was originally found in China (formerly from Manchuria south to Guangxi, and Sichuan to Anhui), North and South Korea (including Cheju Island) (but now probably extinct in both countries), Japan, Russia (a few places in Primorsky in the Far East), Taiwan (extinct in 1969, but subsequently re-introduced), and Viet Nam (probably now extinct). Wild populations are now very localized in China. In Japan, the species ranges widely from Hokkaido, Honshu, Shikoku and Kyushu, islands in the Seto Inland Sea (Awaji, Shodo, and others), Goto Islands, Ika, Yakushima, Mageshima, Kuchinoerabu-shima, Tsushima, and the Kerama Islands (introduced) (Okinawa Prefecture) (Abe 2005).

In China, C. n. mandarinus probably ranged across much of northeastern China, but by the mid-1930s its range had contracted to northeastern Jilin (IUCN 1972, Guo 1992), and is now believed to be extinct (Hu 1998, Smith and Xie 2008). C. n. grassianus ranged throughout western Shanxi Province, China (Ohtaishi and Gao 1990, Guo 1992), and is now believed to be extinct (Hu 1998, Smith and Xie 2008). C. n. kopschi ranged from the Yangtze River Basin eastward to the coast, and south as far as northern Guangdong Province (IUCN 1972); it remains in small numbers in southern China. C. e. taiouanus was widely distributed throughout Taiwan (Green 1989). Free ranging populations were extirpated in 1969, but captive individuals were re-introduced in 1989 (Smith and Xie 2008). C. n. pseudaxis was recorded from Cao Bang, Quang Ninh, Thanh Hoa, Hanoi, and Nghe Tinh provinces in Viet Nam (Dang Huy Huynh et al. 1990), but is probably now extinct in the wild (captive animals remain).

The species has been widely introduced. In the Philippines it was anciently introduced to Solo Island, with questions remaining as to its continued existence there. It was introduced in 17^th century to Kerama Islands (Ryukyu Islands, Japan); and introduced in 19^th-20^th centuries to British Isles, mainland Europe (Armenia, Austria, Azerbaijan, Czech Republic, Denmark, Finland, France, Germany, Lithuania, Poland, western Russia, and Ukraine), New Zealand, USA, and small islands off Japan (Whitehead 1993, Wemmer 1998, Grubb, 2005). It is also widely farmed in Asia, particularly in China (Green et al. 2007, Smith and Xie 2008). Only the native, extant range is included in the distribution map.

The species is heavily depleted in the wild in China, and two of the Chinese subspecies may be extinct (mandarinus and grassianus), and others are threatened. However, large herds exist in captivity in China to meet the demand for velvet antlers used in traditional Asian medicine.

The species occurs in a number of protected areas, including: C. n. sichuanicus in China's Tiebu Nature Reserve (Guo 2000, Guo and Zheng 2005), and Baihe Nature Reserve (Hu 1998); C. n. kopschi in China's Taohonglin Nature Reserve (Hu 1998); C. n. hortulorum in Russia's Dalnevostochny Morskoy, Kedrovaya Pad, Khankaisky, Lazovsky, and Sikhote-Alinsky Nature Reserves; and C. n. taiouanus in Taiwan's Kenting National Park, as a result of The Formosan Deer Restoration Project was initiated in 1984 to re-establish subspecies (Green 1989). Management activities for C. n. keramae have included filling of mine shafts, which posed threats to the deer, as well as the construction of drinking water facilities (IUCN 1972).

C. n. pseudaxis
The Vietnamese Sika Breeding and Conservation Programme was initiated in 1991 with a shipment of ten animals to Europe on breeding loan (Ratajszczak and Smielowski, undated). Recommended conservation actions include improving protection of Cuc Phuong National Park, with particular emphasis on control of poaching and development of a conservation education programme.

C. n. taiouanus
Recommended conservation actions include:

1. Establish a peripheral hunting zone around Kenting National Park to benefit local people, and to minimize impact of deer encroaching into adjacent agricultural land.
2. Expand the area available to the existing free ranging population.
3. Plan, implement, and develop a fully integrated research program focused on the ecology of the free ranging population. Studies should include impact on vegetation and carrying capacity.
4. Develop a long-term strategy for management of Kenting National Park.
5. Plan the establishment of additional free-ranging populations elsewhere in Taiwan.

C. n. keramae
Recommended conservation actions include:

1. Survey status of present populations and undertake studies of existing habitat to determine extent of habitat degradation. Remove feral goats as an urgent priority.
2. Develop a management plan for habitat restoration.
3. Develop a captive breeding programme using animals from surviving populations. Assess possible genetic differences between island populations.
4. Assess attitudes of local people toward conservation, initiate regional conservation education program, and increase law enforcement if necessary.

C. n. mandarinus and C. n. grassianus
Recommended conservation actions include surveys to determine whether or not these two subspecies survive. If populations can be found, activities should include field reconnaissance, population censuses, demographic surveys, ecological studies, and investigations into human use of the deer.

C. n. kopschi
Recommended conservation actions include securing protected habitat, and encourage community development options to mitigate threats, especially poaching.

C. n. sichuanicus
Recommended conservation actions include the implementation management plans in Tiebu and Baihe Nature Reserves, with a particular focus on combating poaching. In 1990, the management plan for Tiebu was being implemented and protection was adequate (Sheng Helin and Zhang Endi pers. comm.).