Southern Red Muntjac is associated with forest, but occurs widely even in heavily degraded forest and, in areas adjacent to forest, in plantations of coffee, rubber, sugarcane, cassava, coconut, and teak (Oka 1998, Laidlaw 2000, Azlan 2006, G. Semiadi pers. comm. 2008). However, its ability to survive in landscape-level stands of teak is probably dependent upon the retention of fringes of secondary growth along streams, gullies and other such features (M. Tyson pers. comm. 2008) and this may be so for the other plantation species, too. Peak densities are probably not in pristine forest: in east Java, secondary forest with gallery forest mosaic seems to hold higher densities, and this muntjac may also benefit even from agricultural conversion at forest edges (M. Tyson pers. comm. 2008). Muntjac (presumed to be largely or entirely M. muntjak) abundance was higher in areas within 1 km of the protected area boundary than in the interior of Bukit Barisan Selatan National Park, Sumatra (although this pattern was only weakly statistically significant), suggesting an association with edge, broken and secondary habitats (O’Brien et al. 2003). In contrast, an avoidance of the edge of the Taman Negara protected area in Malaysia was suspected by Kawanishi and Sunquist (2004). In Danum Valley (Sabah, Borneo), an area with negligible hunting, M. muntjak strongly increased in densities after logging (Heydon 1994, Davies et al. 2001), a weaker increase was found by Duff et al. (1984). In the Sarawak Planted Forests, Bintulu Division, Sarawak, muntjacs (partly this species) are among the commonest species camera-trapped in young acacia plantations (under four years old) and have been seen browsing on young acacia shoots. Footprints are common in the adjacent newly planted areas and forest fragments (Belden Giman pers. comm. 2008). However, this area contains a substantial proportion of natural, if somewhat degraded, forest, which in theory might be found to be necessary for populations in the highly altered habitats. Information on the species in landscape-scale plantations, remote from even secondary forest, has not been traced. Most of its range is dominated by evergreen vegetation, but it readily uses deciduous forests and mosaics of grassland, scrub, and forest (e.g. on Java, Tyson 2007), on Bali and Java, M. muntjak routinely uses woodland savanna as a feeding ground (Oka 1998, S. Hedges pers. comm. 2008).

This muntjac has a wide altitudinal range. In Java, S. Hedges (pers. comm. 2008) has seen them over 0–800 m. In Sumatra, it occurs widely in the lowlands and the second species there, M. montanus, seems to be montane, whether M. muntjak ascends to the highest forests is yet unclear (R.J. Timmins pers. comm. 2008, based on examination of specimens). On Borneo, Red Muntjac lives up to at least 1,000 m asl on the Usun Apau plateau (Payne et al. 1985), who stated that “available data suggests that [M. atherodes] predominates over the Red Muntjac in low hill ranges and coastal regions”, but Meijaard and Sheil (2008) pointed out that still “no robust quantitative data exist to support this [pattern]”. Red Muntjac is scarcer than M. atherodes in Sungai Wain forest, Kalimantan, which spans 30–150 m asl (G.M. Fredriksson pers. comm. 2008), in the Sarawak Planted Forests, Bintulu Division, a mix of acacia plantation and natural forest (Belden et al. 2007, Belden Giman pers. comm. 2008), and (slightly so) in the Ulu Segama area of Danum Valley Conservation Area, Sabah, which lies mostly at about 300 m asl (Siew Te Wong pers. comm. 2008). In Borneo, muntjacs were frequently seen, suspected to comprise roughly equal numbers of Red and Yellow, in the Batang Ai National Park, Sarawak, which lies mostly at 100–760 m asl (Meredith 1995).

The diet is mostly fruits, buds, tender leaves, flowers, herbs and young grass (Kitchener et al. 1990, Oka 1998). In Taman Negara, Malaysia, camera-trapping showed Red Muntjac to be mostly diurnal (Kawanishi and Sunquist 2004) whereas in Gunung Leuser, Sumatra, it was classed as cathemeral (i.e., sporadic and random intervals of activity during the day or night) (van Schaik and Griffiths 1996) and this is true for East Java (S. Hedges pers. comm. 2008), there may be some variation between localities in balance of day and night activity. It is a mostly solitary species that is capable of breeding through the year, and has been stated to be territorial (Kitchener et al. 1990, Oka 1998). However, Tyson (2007) found no evidence of territoriality in radio-collared female muntjacs of Baluran National Park, Java, although range overlap declined in the rainy season compared with the dry season. Nor was there evidence of males using exclusive ranges in any season, or any clear evidence of territorial defence. As in the case of M. vaginalis, occasional sightings of small groups probably refer to mating pairs, or to females with offspring (Oka 1998), or to loose aggregations at abundant food resources (M. Tyson pers. comm. 2008).

Southern Red Muntjac, as defined here, occupies part of the Thai–Malay peninsula and occurs on the main islands of the Greater Sundas (Borneo, Java, Bali and Sumatra) and on various small islands (Chasen 1940, Groves 2003, Meijaard 2003). On Sumatra, it is not geographically limited to southern and eastern parts of the island despite various statements that it is (R.J. Timmins pers. comm. 2008). Taking the northern limit on the peninsula as the Isthmus of Kra (see Taxonomy), M. muntjak (as here defined) is assumed to inhabit southern Thailand and might be found to occur in southernmost Myanmar. It is now extinct in Singapore (Baker and Lim 2008).

Southern Red Muntjac is found in many protected areas throughout its range (GMA Indonesia Workshop). It is a protected game species in West Malaysia under the Wildlife Protection Act of 1972, meaning that it can be hunted only with a license and only outside protected areas (Kawanishi and Sunquist 2004). Indonesian forestry law protects all species of muntjac. Species protection laws relating to ungulates in many areas of Sumatra have not been widely publicized. A significant percentage of Sumatra’s forests are protected, but protected areas and the authorities responsible for conservation of catchment forests are often under-funded and almost all are grossly understaffed so that there is little ranger presence in the field. Where there are field ranger teams, these focus generally on flagship species such as Asian Elephant Elephas maximus, Sumatran Rhinoceros Dicerorhinus sumatrensis or Tiger Panthera tigris, although Tiger protection rangers do also conduct ungulate protection activities and in 2007 three hunters arrested in the national park with two muntjacs carcasses received custodial sentences at Kerinci district court (D. Martyr pers. comm. 2008). Much of Java’s remaining forest is officially protected. Heavy hunting with shotguns was found to be a severe problem for larger mammals and birds across Sarawak and the need for its control (of guns and of sale of ammunition, with firm legal underpinnings) was recognised in the Master Plan for Wildlife in Sarawak (Wildlife Conservation Society and Sarawak Forest Department 1996). As everywhere, people devise ways for circumventing the controls (illegal trade in bullets and locally made shot-guns, called bekakok, which have no administrative or legal paper-trail) and strong enforcement is required for the foreseeable future.

There seem to be no species-specific conservation measures in need of implementation, above turning existing laws on protected areas and protected wildlife into reality, with a particular focus on eradicating wildlife trade.