The Greater Oriental Chevrotain is almost completely sympatric with T. kanchil, but the degree of syntopy is less clear. In the lowlands of Borneo both occur but T. napu apparently ranges to higher altitudes (up to at least 1,000 m asl) than does the latter (Payne et al. 1985). Relevant comparisons have not been traced for the other main occupied landmasses. Duckworth (1995) considered that the chevrotains demonstrably common at Similajau National Park were largely or entirely Greater, but on altitude use as given in Payne et al. (1985) it would seem surprising if Lesser did not occur. However, Matsubayashi and Sukor (2005) found at Tabin Wildlife Reserve, Sabah, that T. kanchil was almost absent from mature forest, all animals in such habitats being T. napu. Almost all observations from Similajau were from climax forest. Much more information of chevrotain habitat use in areas of sympatry is desirable before firm species-level conclusions can be drawn. T. napu was found typically to range 19 ha in old logged forest and 7 ha in primary forest, this difference again suggesting an association with primary forest (Heydon 1994). Heydon and Bulloh (1997) suggested the obligate frugivory of chevrotains limited their ability to compensate for logging-led loss of fruit trees by browsing the abundant regrowth of logging areas. The abundance of Tragulus spp. (T. napu and T. kanchil combined, with no information on the proportions or even confirmation that both species were present) was higher (strongly statistically significantly so) in areas within 1 km inside the boundary of Bukit Barisan Selatan National Park, Sumatra than in the interior of the park, suggesting higher numbers in somewhat encroached habitat. Also at this site, Tragulus was more then nine times as abundant in areas of the park with low than with high human population density within 10 km of the park boundary, suggesting limited resilience to human presence, presumably the effects of hunting (O'Brien et al. 2003); note that it is not confirmed that this information refers, even in part, to T. napu. The genus (presumably including this species) was ubiquitous in a study of virgin jungle reserves (VJRs) of West Malaysia which paired each of seven VJRs with a nearby unprotected area with seriously encroached habitat (Laidlaw 2000). The ability of T. napu to use plantations is probably low, because all (the admittedly relatively few) sources agree that it does not persist well in secondary or logged forest. Moreover, Belden Giman (pers. comm. 2008), in extensive observations at Sarawak Planted Forests, Bintulu, Sarawak, has never recorded T. napu in any of the blocks of monoculture plantations there, despite many records of T. kanchil. Given the pace of conversion of forests to plantations across the rane of T. napu, clarification of its degree of plantation use is urgent.

Competition with T. kanchil is not pronounced. In Tabin Wildlife Reserve, Sabah, T. napu was largely confined to mature forest with T. kanchil only in immature forest (Matsubayashi and Sukor 2005). In unlogged forest at Danum Valley, Sabah, T. napu was significantly more common than T. kanchil, but following logging, the numerical dominance of T. napu declined, and in 2–5-year-old regrowth T. kanchil was the commoner species. By 12 years post-logging, T. napu had reasserted its numerical predominance (Heydon 1994).

Tragulus spp. are generally thought to be nocturnal, and at two sites in Borneo, they comprised over half the contacts of spot-lighting surveys (Duckworth 1997), but Matsubayashi and Sukor (2005) found substantial amount of both day- and night-time activity in this species. Duckworth (1997: 186–187) pointed out that most chevrotains spotlit in Similajau National Park, Sarawak, (identified as T. napu) were sitting around resting. The related T. kanchil was considered highly solitary by Matsubayashi et al. 2006) and this may also be somewhat true for T. napu; Duckworth (1995: 177) observed chevrotains identified as T. napu 14 times, of which 12 records involved singles and two involved duos in apparent association.

Collation of information from general sources suggests the following, but the contribution of information from T. nigricans to these conclusions is unknown, so their reliability for T. napu s.s. should be considered preliminary. Females gestate for 152–155 days and give birth to one or, rarely, two young. Young wean at 2–3 months, and reach sexual maturity at 4.5 months. Animals live up to 14 years. The female can be pregnant throughout her adult life, often having just an 85–155 minute 'breather' between giving birth and becoming pregnant again. The young are born fully developed, and can stand within 30 minutes of birth. Mothers nurse their young standing on three legs. They are generally solitary.

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Greater Oriental Chevrotain populations are not well studied, in part reflecting a general lack of research interest in the genus and in part its almost complete sympatry with the Lesser Oriental Chevrotain, from which separation requires care under field conditions (Duckworth 1997; Matsubayashi and Sukor 2005). It seems to be relatively common on at least Borneo (Payne et al. 1985; Belden Giman pers. comm. 2008). In Thailand, at the northern margin of its range, it is generally rare (Anak Pattanavibool pers. comm. 2008); for example, during the flooding of the Chiew Larn Reservoir (Surat Thani province; about 9°00′N, 98°45′E; 20–130 m asl), only six Greater Chevrotains were ‘rescued’ compared with 172 Lesser Chevrotains (Nakasathien 1989). The genus is commonly camera-trapped and recorded by signs on Sumatra and in West Malaysia (Laidlaw 2000; O'Brien et al. 2003; Kawanishi and Sunquist 2004; Azlan 2006) and in far southern Myanmar (Lynam 2003; the identifications to species should be disregarded). At the Danum Valley, Sabah (East Malaysia), densities were recorded as 32–72 animals per km² in primary habitat; they were more scarce in selectively logged areas, with densities of 6–16 animals per km², indicating a marked decrease in T. napu in selectively logged forest vs unlogged (Heydon and Bulloh 1997, Davies et al. 2001). Because population densities of Southern Red Muntjac Muntiacus muntjak and Sambar Rusa unicolor rose in the logged areas in this same study, the decline in chevrotains presumably reflects habitat factors rather than the secondary complication of logging-induced hunting. Population densities for Tragulus spp. (presumably including this species) in Taman Negara, Malaysia, were taken to be 0.37–0.83 per km² (Kawanishi and Sunquist 2004). Duckworth (1995) considered that the chevrotains demonstrably common at Similajau National Park in 1986 and 1995 were largely or entirely Greater (see Habitat and Ecology).

Decreasing

Hunting and habitat loss occur at high levels almost throughout Greater Chevrotain’s range, but the species is said to be relatively resilient. However, few data to support this assessment have been traced, particularly because most key studies have not within the Sundaic region identified chevrotains to species. Thus, while clear that the genus remains widespread and common in the face of these threats, there seems to be little publicly available evidence that T. napu specifically does so, and reasonable evidence that it is not very adaptable to forest degradation (see Habitat and ecology). However, on the assumption that most chevrotains above 100 m asl on Borneo are this species rather than T. kanchil, Borneo at least retains large populations. Greater Oriental Chevrotain is extinct on Singapore (K. Lim pers. comm. 2008), although the relative contributions of hunting versus habitat perturbation are not known.

Poaching pressure in Kerinci-Seblat National Park, Sumatra, among snared ungulates was greatest for muntjacs and lowest for chevrotains, as assessed by diameter of the cable (Linkie et al. 2003). Chevrotains were scarcer in areas of higher human use (and thus hunting) of Bukit Barisan Selatan National Park, Sumatra (O'Brien et al. 2003; see Habitat and ecology). Bennett et al. (2000) profiled the effects of hunting in both Bornean states of Malaysia (Sarawak and Sabah), each with eight study areas, upon chevrotains (not distinguished to species) through a lengthy hunting study in February 1993 to June 1995. They constituted 8–9% of animals killed. No direct or index measure of chevrotain densities was possible at these sites to determine what effects, if any, such heavy hunting was having on chevrotains. Chevrotains are among the most favoured wild meat by inhabitants of the Sarawak Planted Forests area, Bintulu, Sarawak, after Sambar Rusa unicolor and wild pigs Sus (Belden Giman pers. comm. 2008).

Hunting and habitat loss occur at high levels almost throughout this species’s range. Adequate legal basis exists in all range states to control both threats (through protected areas and regulations governing wildlife trade and hunting). The chief need is for effective translation of these laws into action. There are no obvious species-specific needs additional to general consolidation of protected areas and enforcement of hunting and wildlife trading laws.

The paucity of Sundaic studies determining chevrotains to species shows admirable caution but hinders assessments of this species’s status. Better data would be useful to confirm the opinion-based conclusion here that this is a resilient species, and to investigate further habitat use, in areas where it overlaps with T. kanchil and in those (probably, primarily at higher altitude) where it does not.