Form

The pelage of Rusa unicolor is generally shaggy and coarse, and individual hairs are “not distinctly banded with different coloured rings” (Lydekker 1898:145). Hairs on R. unicolor are thickest on the neck, back, and abdomen; thinner on dorsal side of the tail and legs; and thinnest around the preorbital glands, temples, and gaskins (lower thighs—Sokolov et al. 1987). Guard hairs of R. unicolor have a mean medullary width of 186 µm and mean cortical width of 29.0 µm (Sheng et al. 1993). Measurements (µm) of axial hairs vary depending on the location on the body; ventral neck hair: cortical thickness  =  15.0, medullary diameter  =  75.0, root diameter  =  147.0, hair diameter above the root  =  93.3; ventral tail hairs: 10.6, 75.0, 166.6, 107.0; lateral gaskin hairs: 10.0, 40.0, 86.7, 66.5; lateral thigh hairs: 10.0, 37.5, 80.0, 60.0; abdomen hairs: 10.0, 75.0, 100.0, 66.6; preorbital region hairs: 10.0, 22.2, 63.3, 50.0; and forehead hairs: 12.5, 55.0, 70.0, 43.3 (Sokolov et al. 1987).

Related to the tropical origin of R. unicolor, development of the undercoat in young R. unicolor is modest or lacking; 2 of 4 captive 165-day-old (± 9.8 SE) R. unicolor did not have an undercoat, and the proportion of the undercoat relative to the total pelage weight on the other 2 young was only 0.7% (Semiadi et al. 1996). Pelage characteristics of those young R. unicolor, when present, were: depth of fiber undercoat, 26.8 mm; weight of fiber undercoat, 114 g/m²; length of fiber undercoat, 20.3 mm; length of guard hairs, 44.0 mm; diameter of undercoat fibers, 18.0 µm; and diameter of guard hairs, 277.0 µm (Semiadi et al. 1996). Shedding is said to occur in “large tufts … the old hair coming away in sections” (Brander 1923:169).

Although numerous antler measurements have been published for R. unicolor (e.g., Downes 1983b; Lydekker 1898; Pocock 1943b; Whitehead 1993), skull measurements are less common. Nasal bones on the skull of R. unicolor “develop a plate at the posterior expansion, which tends to grow over the lachrymal vacuity” (Lydekker 1898:146, 1915); the vacuity is longer than in other cervids; and the skull has a robust appearance (Pocock 1943b; Fig. 4). The small auditory bullae rarely project below the basioccipital, and the preorbital “gland-pit” is large, usually exceeding the diameter of the orbit (54–64 mm in India—Pocock 1943b:27). Representative condylobasal lengths of skulls (mm, sexes combined) are 350–408 from India, 332–395 from Sumatra, 330–345 from Borneo, and 312–328 from Taiwan (Lyon 1906; Pocock 1942b, 1943b), illustrating the general decrease in size from west to east (Geist 1998). More recent representative mean skull measurements (mm ± SD) of R. unicolor include: greatest length of skull, 357.5 ± 35.0; condylobasal length, 340.5 ± 35.3; basal length, 318.6 ± 33.0; palate length, 212.0 ± 22.5; condylar breadth, 65.4 ± 7.1; rostrum length, 199.1 ± 26.7; nasal length, 104.7 ± 14.7; biorbital breadth, 139.4 ± 14.8; maximum breadth of nasals, 39.4 ± 7.4; interorbital breadth, 88.9 ± 13.5; and braincase breadth, 86.7 ± 7.5 (n  =  27–30, males and females combined—Meijaard and Groves 2004).

Fig. 4

Ventral, dorsal, and lateral views of skull and lateral view of mandible of male Rusa unicolor brookei (British Museum [Natural History], specimen 1.3.13.1) with pedicels after antler shedding, collected in Sarawak, northwestern Borneo. Greatest length of skull is 354 mm.

Unlike New World deer, new antlers of Old World deer such as R. unicolor begin to grow immediately after the previous antlers are shed (Geist 1998). During growth, antlers are covered in modified skin, or velvet, that nourishes the growing bone (Bubenik 1993); developing antlers and velvet of various cervids are prized in Asian medicine (Peacock 1933; Thom 1937) and grown commercially for that market (Luick 1983). Early anecdotal accounts suggested that R. unicolor did not replace its antlers annually (Baker 1898; Fletcher 1911; Gilbert 1888; Phythian-Adams 1951), but this is not the case and is probably related to the lack of a pronounced breeding season and observations of males in various stages of antler growth and ossification throughout much of the year (Brander 1923; Putman 1988; Schaller 1967; Thom 1937)—a pattern that persists even if males are transplanted to more temperate areas (Lao 1968).

Unlike other cervids, particularly northern boreal species, antler bone of R. unicolor, as well as that of primitive species of Axis and Rucervus, has a very thick cortex suggesting rapid building processes of the osteon; a tubular cavity of 8 mm in diameter, apparently a blood sinus suggesting that the some bone remains alive after shedding of velvet; and concave seals in young males changing to flat seals in prime males (Acharjyo and Bubenik 1983). Males can be grouped into general age classes ≤ 6 years of age based on their antler characteristics (Downes 1983b). Length and mass of antlers increase with age but most notably in a male's 7th year; thereafter, length and mass change little (Downes 1983b), although Baker (1898) contended that maximum antler size (and mass) may not be achieved until a male is about 10 years old. Yearling males have a single spike antler, and 2- to 3-year-old males have a brow tine and main beam; both tend to have smooth antlers. By 4 years of age, males have “roughly corrugated” antlers with the typical 3 tines (Brander 1923:171; Downes 1983b). Yearling and adult females can be differentiated based on body mass, but no external characteristics are useful for aging adult females.

The dental formula of adult R. unicolor is typical of cervids: i 0/3, c 1/1, p 3/3, m 3/3, total 34 (c1 incisiform). Upper canines may be absent; only 2 of 83 R. unicolor skulls had them in Sariska Tiger Reserve, India (K. Sankar, pers. comm.). Eruption of the 1st permanent teeth (m1–M1) begins at about 1 month, followed by m2–M2 at about 8 months and then i1–I1 at about 11 months; all permanent teeth are present by about 2.5 years (Slee 1984)—a pattern useful for aging (Humphries and Rowler 1976). Molars are notably hypsodont with “small accessory columns” (Blanford 1888:543); 2 or 3 cusps occur on the occlusal surfaces of the premolars and molars forming sharp lingual crests; and incisors are “hockey stick like” in shape (Shalini et al. 2004a:1102). Representative tooth measurements (mean ± SE, cm) of an adult R. unicolor are crown length: p1  =  0.60 ± 0.01, p2  =  1.36 ± 0.01, p3  =  1.30 ± 0.04, m1  =  1.66 ± 0.11, m2  =  1.83 ± 0.02, and m3  =  1.95 ± 0.04; and crown width: p1  =  0.56 ± 0.03, p2  =  0.77 ± 0.5, p3  =  0.73 ± 0.05, m1  =  1.06 ± 0.03, m2  =  1.32 ± 0.01, and m3  =  1.42 ± 0.02 (Shalini et al. 2004a).

Tooth eruption-wear and cementum annuli of R. unicolor in Gir National Forest, India, were highly correlated (r²  =  0.974—Berwick 1974), but irregular layering of cementum was reported in R. unicolor from Ruhuna National Park, southern Sri Lanka, making interpretation of age more difficult (Ashby and Santiapillai 1986). Patterns of growth layers in dental cementum of the 1st mandibular molar of R. unicolor relative to age have been investigated in New Zealand and are comparable to those of red deer (Douglas 1970; Slee 1984). Flynn et al. (1990) noted that it was difficult to age R. unicolor from tooth eruption and wear alone; estimates could be off by 12 months.

Anatomy of the 4-chambered stomach, particularly the rumenoreticulum, and poorly developed papillae on the roof of the rumen suggest that R. unicolor should be a grass-roughage feeder (Stafford 1995). Various attributes of each chamber are rumen: volume  =  9–20 l; reticulum: volume  =  0.2–1.0 l, wall thickness  =  1.5–4.0 mm; omasum: volume  =  0.2–1.1 l, mass  =  360–568 g, wall thickness  =  2.0–2.75 mm; and abomasum: volume  =  0.4–1.2 l, length  =  25–35 cm (9 male and 4 female R. unicolor, aged 1–5 years—Stafford 1995). Lengths (cm) of lower digestive organs of R. unicolor are: small intestine, male 480 and female 360; large intestine, male 450 and female 360; and cecum, male 45 and female 35 (Stafford 1995). Compared with other ruminants, those lengths are very short, and the near 50∶50 ratio of small to large intestinal length of R. unicolor is in contrast to that of the red deer, a true grass-roughage feeder, which has a ratio of about 75:25 (Dryden 2008; Stafford 1995). Combined, intestinal characteristics of R. unicolor suggest a species capable of efficiently digesting diets of grasses and browse, or an intermediate feeder. Morphology of the scapula (Sarma et al. 2003), atlas (C1 vertebra), and axis (C2—Shalini et al. 2004b) of R. unicolor also has been described.

The reproductive tract of female R. unicolor generally is comparable to that of other cervids (Plotka 1999). R. unicolor has a bicornuate uterine horn with 3 mesometrially located caruncles, and the 3 associated cotyledons, in each horn; the 6 placental cotyledons are large (late gestation: 300–320 g and 5 by 9 cm); and the placenta implants on the 3 mesometrial caruncles of both horns (Benirschke 2002). A single corpus luteum was noted per pregnancy in 5 females from Perak, Malaysia (Khan and Khan 1968). The uterus of a near-term female R. unicolor from the San Diego Zoo was 130 cm long, and the placenta was epithelio-chorial without invasion into the maternal tissue (Benirschke 2002). The 7-cm umbilical cord in that gravid female was not spiraled, contained 4 blood vessels, and had a large, highly vascularized allantoic duct (Benirschke 2002).

Mean (± SD) testicular and semen characteristics of 15 male R. unicolor from Taiwan include: single testicular volume, 126.9 ± 72.7 cm³; scrotal circumference, 23.5 ± 5.5 cm; semen volume, 1.4 ± 0.7 ml; spermatozoa concentration, 557 ± 344.8 × 10⁶/ml; spermatozoa motility, 75.5% ± 9.3%; and normal spermatozoa morphology, ≥80% (Wu et al. 2002). Mean (µm ± SD) lengths of individual spermatozoa include: total length, 65.4 ± 1.7; head length, 9.3 ± 0.5; midpiece length, 12.9 ± 0.7; and tail length, 43.2 ± 1.8 (Wu et al. 2002). Fetal testes of R. unicolor have binucleated trophoblastic cells on the villi and histological characteristics that suggest a lack of active fetal gonadotropins (Benirschke 2002).

Function

Mean (± SD) hematological values of Rusa unicolor are: hematocrit, 37.7% ± 3.2%; red blood cells, 5.70 ± 0.22 × 10⁶ cells/ml; hemoglobin, 13.0 ± 0.9 g/dl; mean corpuscular volume, 66.0 ± 3.2 µm³; white blood cells, 4.79 ± 1.18 × 10³ cells/ml; eosinophils, 2.58% ± 2.75%; basophils, 1.43% ± 1.68%; and monocytes, 1.82% ± 0.76% (n  =  3 adults—Peinado et al. 1999a). Representative mean (± SD) blood chemistry and serum values of R. unicolor are: aspartate aminotransferase, 24.4 ± 4.1 IU/l; alanine aminotransferase, 28.7 ± 4.7 IU/l; creatinine phosphokinase, 205.0 ± 122.0 IU/l; lactic dehydrogenase, 452 ± 49 IU/l; gamma glutamyl transpeptidase, 38.1 ± 19.6 IU/l; alkaline phosphatase, 197 ± 74 IU/l; glucose, 8.50 ± 1.32 mmol/l; urea, 6.94 ± 2.77 mmol/l; uric acid, 29.1 ± 10.7 mmol/l; creatinine, 238 ± 23 mmol/l; cholesterol, 1.49 ± 0.42 mmol/l; triglycerides, 0.13 ± 0.05 mmol/l; protein, 7.45 ± 0.34 g/dl; albumin, 71.9% ± 5.7%; albumin–globulin ratio, 2.6 ± 0.7; and osmolality, 289 ± 6 mOsm/kg (n  =  3 adults—Peinado et al. 1999b).

Unique among cervids, reproductively active male R. unicolor, females during late pregnancy and lactation, and even young-of-the-year can have a “sore spot” of 10–15 cm (Davar 1938; Geist 1998; Kurt 1978; Peacock 1933; Schaller 1967; U Tun Yin 1967) on their throats, ventrally halfway down the neck (Evans 1912). This spot is apparently glandular, centered in a whorl of hair, and often, but not always, exuding “whitish-looking oily or watery substance” from a blood-red spot (Davar 1938; Evans 1912; Morris 1938; Phythian-Adams 1951; Thom 1937:315). Thom (1937:313–317) summarized the colorful early speculation on the cause or function of the sore spot, which included disease (e.g., leprosy in Thailand), consumption of “wild olives,” ticks or some other parasite (Davar 1938; Evans 1912; Peacock 1933; Whitehead 1972), irritation from rubbing or moving through thick coarse grass, or a wound from an attack by a marten, likely Martes flavigula. The sore spot apparently does not occur (or has not been observed) on R. unicolor in Sri Lanka (Kurt 1978), among introduced populations on St. Vincent Island, Florida (Shea et al. 1990), and Australia (Downes 1983b), or under some captive conditions (Evans 1912; Mary and Balakrishnan 1984; Thom 1937; U Tun Yin 1967). Richardson (1972:58) noted that all sexes and ages of introduced R. unicolor in Texas had a “whirl of hair” on the throat that was “relatively bare,” but he did not notice any secretions or blood. Perhaps this “gland” does not manifest itself when densities are relatively high or group size is large, as in Sri Lanka or under confinement, suggesting a role in communication (scent dispersal—Mary and Balakrishnan 1984; Schaller 1967), particularly during breeding and at low densities (Geist 1998). The sore spot is associated with the breeding season in some places in India (Johnsingh 1980), but it does not bleed or secret any substance, even during breeding, in western or northern India (K. Sankar, pers. comm.).

Muscle tissues of R. unicolor vary (mean ± SD) in their composition: longissimus dorsi, 74.40% ± 0.29% moisture, 2.93 ± 0.41 g fat/100 g dry weight, 21.99 ± 0.34 g fat/100 g wet weight, 101.30 ± 0.39 g cholesterol/100 g dry weight, and 4.73% ash, and biceps femoris, 74.52% ± 0.42% moisture, 4.06 ± 0.41 g fat/100 g dry weight, 21.83 ± 0.11 g fat/100 g wet weight, 79.52 ± 0.21 g cholesterol/100 g dry weight, and 2.35% ash (Dahlan and Norfarizan-Hanoon 2008). Detailed information on fatty acid profiles in muscles of R. unicolor was provided by Sinclair et al. (1982) and Dahlan and Norfarizan-Hanoon (2007).

During captive feeding trials with <14-month-old R. unicolor on an ad libitum diet of chaffed alfalfa (Medicago sativa) hay and with a voluntary intake of 58.7 and 55.9 g/kg body weight^−0.75/day in summer and winter, respectively, numbers of eating and ruminating bouts, and their duration, were about equally distributed during the day (0600–1800 h) and night (1800–0600 h) in both seasons (Semiadi et al. 1994a). Captive R. unicolor fed for 6.4 h in summer and 4.2 h in winter and ruminated for 9.2 h in summer and 9.1 h in winter (Semiadi et al. 1994a). Metabolizable energy for maintenance was 474 kJ/kg body weight^−0.75/day; nitrogen retentions (h) as a percentage of intake on 26.6–47.3 and 33.7–44.4 g N/day were 15.1–31.7 and 15.3–29.4, respectively (Semiadi et al. 1998). Similar captive experiments showed that young R. unicolor responded to low-quality diets by lowering voluntary food intake, increasing chewing activity, and conserving nitrogen compared with young red deer (Howse et al. 1995; Semiadi et al. 1994a). The modulus of fineness (Poppi et al. 1980) of fecal particle size from digesta residue suggests that R. unicolor is an intermediate feeder (modulus of fineness  =  2.21); percentage of fecal particles passing through various sieve sizes are: 4-mm sieve, 0.33%; 2-mm sieve, 1.15%; 1-mm sieve, 5.36%; 0.25-mm sieve, 16.74%; and <0.125-mm sieve, 44.32% (Clauss et al. 2002). Additional insight on fecal particle size during captive feeding trials was provided by Semiadi et al. (1994a).

During experiments with four 165-day-old (± 9.8 SE) R. unicolor in metabolic chambers at 5°C and 20°C without and with wind (6 km/h), respectively, mean heat production (kJ/kg body weight^−0.75/day) was 615, 659, 460, and 490 (Semiadi et al. 1996). When ambient temperature was dropped from 20°C to 5°C, heat production increased 34% without wind and 44% with wind; lower critical temperature was 11.6°C without wind and 14.0°C with wind (Semiadi et al. 1996). Compared with young red deer (Semiadi et al. 1996), metabolic responses of young R. unicolor suggested that, given their tropical affinities, they need more shelter and food during cold weather, not unlike Crandall's (1964) observations that adults of R. unicolor seek shelter during cold weather at the New York Zoological Park.

Population characteristics

Despite the widespread distribution of Rusa unicolor in southern Asia and use of many different habitat types, it is no longer abundant throughout most of its native range, except in some protected areas (Sankar and Acharya 2004; Timmins et al. 2008). Because of its predominantly crepuscular to nocturnal behavior, small group size, and general shyness, it is difficult to census accurately (Eisenburg and Lockhart 1972; Schaller 1967). Observed densities of R. unicolor are generally low but vary depending on season and related grouping behavior, habitat conditions in native and introduced areas, competition, predation, and degree of protection. Representative densities are: 0.24–10.70 individuals/km² in moist and dry deciduous tropical forests in India (Bagchi et al. 2003b; Balakrishnan and Easa 1986; Berwick and Jordan 1971; Biswas and Sankar 2002; Jathanna et al. 2003; Karanth and Sunquist 1992, 1995; Khan et al. 1996; Kurt 1978; Varman and Sukumar 1993); 0.70–1.17 individuals/km² in lowland dry-zone scrub jungle in Sri Lanka (Eisenberg and Lockhart 1972); 2.0–11.5 individuals/km² in riverine and Shorea forests and tall-grass habitats in Nepal (Seidensticker 1976b); 1.9–4.2 individuals/km² in dry tropical forests in Thailand (Srikosamatara 1993); 0.62–1.42 individuals/km² in lowland rain forest in Sumatra, Indonesia (O'Brien et al. 2003); and 1.76–6.01 individuals/km² in feral populations in Florida (Flynn et al. 1990). Relative abundance indices of R. unicolor in Bukit Barisan Selatan National Park, Sumatra, Indonesia, are 5.6 times higher in areas of low human density (0–9 villages/area) than areas of high human density (16–30 villages/area—O'Brien et al. 2003).

Longevity records in captive subspecies include 6 years, 7 months for a male R. u. brookei, 7 years, 11 months for a male R. u. swinhoii, 26 years, 5 months for a female R. u. equina, and 28 years, 5 months for a female R. u. unicolor (Manville 1957; Weigl 2005). Based on life-table analyses, a typical wild R. unicolor dies before about 12 years of age in Gir National Forest, India (Berwick 1974). Mean life expectancy of wild R. unicolor in Ruhuna National Park, southern Sri Lanka, was about 10 years, with no difference between sexes; maximum life expectancy was 24 years; and somewhat surprisingly, mortality of individuals < 2 years old was only about 6%/year (Ashby and Santiapillai 1986). Maximum life span of exotic R. unicolor in New Zealand is estimated at 12 years for males and 17 years for females (Forsyth and Duncan 2001).

Age structures from populations in India suggest relatively low productivity and male-biased mortality: 43–45% adult females, 5–11% yearling females, 16–19% adult males, 11% yearling males, 19–20% young-of-the-year (n  =  242 [Karanth and Sunquist 1992], n  =  674 [Karanth and Sunquist 1995]); 51.4%, 9.8%, 15%, 3.5%, 20.4% (n  =  363—Schaller 1967); and 58%, 7%, 21%, 2%, 12% (n  =  1,242—Varman and Sukumar 1993). In Gir Lion Sanctuary, India, average age structure in 1987–1989 was 57.6% adult females, 31.4% adult males, 3.7% yearlings, and 7.1% young-of-the-year, suggesting very low recruitment (Khan et al. 1995). Schaller (1967) contended that about 50% of young R. unicolor in central India die before reaching 1 year of age; similarly, Berwick (1974) observed high mortality of young in Gir National Forest in western India.

Adult sex ratios of R. unicolor favor females, sometimes remarkably: 6 males ∶ 100 females (Ngampongsai 1977); 16–50:100 (Johnsingh 1983); 26–53:100 (Berwick 1974; Berwick and Jordan 1971); 27:100 (Varman and Sukumar 1993); 28:100 (Mohammad Ali 1982); 29:100 (Schaller 1967); 54:100 (Khan et al. 1995); and 83:100 (Bagchi et al. 2008). Comparison of sex ratios from kills by Indian tigers (Panthera tigris tigris—120 males ∶ 100 females) and from direct observations (30∶100) in Kanha National Park, central India, suggests differential predation on young and adult males (Schaller 1967). Where major predators are rare or lacking, male numbers seem to be higher; for example, Eisenburg and Lockhart (1972) noted an usually high male-dominated sex ratio of 123 males ∶ 100 females in Sri Lanka, and Flynn et al. (1990) noted 73 males ∶ 100 females in Florida where R. unicolor was introduced.

A typical adult male R. unicolor is solitary throughout much of the year, and its low observability may bias estimates of sex ratios. Nevertheless, high rates of mortality are common for male ungulates in general, and disparate sex ratios of R. unicolor could be the result of rutting mortality among mature males. Combat between mature males in rut has been described as antler-to-antler “pushing matches,” but “often severe wounds are inflicted by the [pronounced and lethally angled] brow antler;” Fletcher (1911:346) observed a likely lethal blow by the victorious male to the abdomen of the fleeing vanquished, which he shot. Phythian-Adams (1951:7) noted that mature males “fight desperately” and found 2 dead males with their antlers interlocked. Although mature males give the “impression of harmony” in captivity, deaths have been reported from rutting injuries (Semiadi et al. 1994b:82). Such mortality is difficult to quantify in the wild, but for related North American elk, rutting mortality may be more common than once thought (Leslie and Jenkins 1985).

Space use

Although Rusa unicolor is remarkably flexible in its habitat affinities, it prefers areas relatively free from human disturbance (Kushwaha et al. 2004; O'Brien et al. 2003). It mainly prefers forested landscapes (Sankar and Acharya 2004). In India, it occurs “wherever there are hilly ranges covered with jungle” and has an affinity for the tall-grass ecotone between dense forest and open grasslands (Fletcher 1911:333; Lydekker 1916; Ngampongsai 1977) where it finds food and protective cover. In Nepal, R. unicolor uses dense climax sal forests, where it may have a competitive advantage (Dinerstein 1979, 1980). In Thailand, R. unicolor tends to preferentially bed where forest canopy cover is >90% with north and east aspects (Brodie and Brockelman 2010). R. unicolor is nonmigratory over much of it range, but in mountainous areas, it may leave higher elevations during winter (Green 1987). R. unicolor is rather sedentary, although movements become more extensive during rut (Schaller 1967).

Size of home range of deer varies depending on habitat quality and conditions (Putman 1988), and given the vast geographical distribution of R. unicolor, its home-range size is probably quite variable, although few studies have been conducted in its native habitat. In Sariska Tiger Reserve, India, mean annual home ranges (ha) were 1,500 for males and only 300 for females (Sankar 1994 [not seen, cited in Sankar and Acharya 2004]). Where R. unicolor has been introduced in coastal Texas, annual home ranges (ha) from direct observations of known individuals were larger for males (69–124, n  =  4) than females (38–51, n  =  2); smallest seasonal home ranges occurred in winter (4 for females and 10–86 for males—Richardson 1972). On St. Vincent Island, Florida, mean annual home ranges (ha) of radiocollared individuals were 201.2 for females and 406.6 for males; seasonally, home ranges of females (summer, 36.8; autumn, 45.4; winter, 83.0; spring, 59.8; n  =  4) were smaller than those of males (summer, 81.2; autumn, 23.7; winter, 106.2; spring, 189.3; n  =  3), except in autumn (Shea et al. 1990). Home-range size in New Zealand is comparable to that in Florida (Lo 1985 [not seen, cited in Shea et al. 1990]). Reflecting a generally sedentary nature of R. unicolor, introduced populations in New Zealand dispersed only 0.64 km/year from the time of release, the lowest level of 9 exotic translocated ungulates (maximum 8.64 km/year for chamois [Rupicapra rupicapra]—Caughley 1963).

Diet

Rusa unicolor is a herbivorous ruminant with great variation in dietary selection depending on forage availability (Geist 1998; Schaller 1967). Lewis et al. (1990) provided a cogent review of the food habits of R. unicolor and noted that its ability to consume a wide variety of grass and browse (Fig. 5), while meeting nutritional needs, is correlated with its wide geographical range (Timmins et al. 2008) and success when translocated to alien continents (Fraser et al. 2000; Harris 1971; Kelton and Shipworth 1987; Lewis et al. 1990). Although the size of R. unicolor suggests that it could favor grasses and herbs, it is an intermediate feeder and consumes a great variety of shrubs and trees (Khan et al. 1994; Schaller 1967; Srivastava et al. 1996)—not unlike the larger North American elk in temperate coastal forest in the Pacific Northwest (Leslie et al. 1984).

Fig. 5

Mature female Rusa unicolor browsing from her hind legs, a common position of the species but relatively uncommon in other cervids, Kheoladeo National Park, Bharatpur, Rajasthan, northern India, February 2006; note the relatively long tail. Males also assume this position to mark branches as high 3 m at “stomping grounds,” used repeatedly during rut. Photograph courtesy of Lee Dalton ( http://www.leedaltonphotography.com) used with permission.

Dietary selection of R. unicolor varies considerably depending on season, location, habitat variety and its effect on forage availability and quality, competitive interactions, and human activities (Kushwaha et al. 2004), whether in native habitat (Bagchi et al. 2003a; Johnsingh and Sankar 1991; Khan 1994; Padmalal et al. 2003; Schaller 1967; Shukla and Khare 1998) or introduced locations (Kelton and Skipworth 1987; Shea et al. 1990; Stafford 1997). In India, R. unicolor consumes a greater variety of plants than any other ungulate (Schaller 1967), often uses cultivated areas, and is not deterred by fences as high as 2 m (Baker 1898; Brander 1923).

Rusa unicolor is 1 of 3 primary consumers of the fleshy fruits of Choerospondias axillaris, a large tropical canopy tree in Thailand, but it deposits most of its seeds under the female canopy trees where regeneration is low (Brodie et al. 2009). Low crude protein and low plant cell-wall contents of R. unicolor feces in November–December suggest that fruits were important dietary constituents in the Indian Himalayas (Green 1987). Although R. unicolor ate fleshy and dry seeds in Nepal, it was not considered an important seed disperser (Dinerstein 1989).

Limited information exists on the nutritional ecology of R. unicolor, but as with most dietary generalists, it is presumed that nutritional needs are met by varying dietary selection throughout the year. Using fecal nitrogen and other fecal constituents (e.g., Leslie et al. 2008; Leslie and Starkey 1985), Green (1987) demonstrated that R. unicolor in the Indian Himalayas obtained the highest dietary quality, relative to crude protein, in spring and summer and that high ash content in spring, summer, and autumn suggested ingestion of soil, perhaps as a buffer to presumed high levels of ingested volatile oils common in woody species. In Horton Plains National Park, Sri Lanka, nitrogen in feces of R. unicolor suggested highest nutrient availability in May–June (Padmalal et al. 2003). Similar to North American elk in temperate rain forests (Leslie et al. 1984), R. unicolor in the Indian Himalayas consumed significant qualities of ferns (about 40% of the diet) in winter, as well as bamboo and woody browse (Green 1987:figure 10). Despite deficiencies of copper and selenium in soils in New Zealand, introduced populations of R. unicolor obtain sufficient amounts of dietary selenium (>850 nmol/kg in 22 liver samples) and vitamin B12 (>220 nmol/kg), but often insufficient amounts of copper (<100 µmol/kg—Stafford 1997).

Rusa unicolor regularly drinks water (Hose 1893a; Peacock 1933; Thom 1937; Whitehead 1972) and usually is not far from free water (Brander 1923; Sankar and Acharya 2004; Fig. 6). In Sri Lanka, temporary aggregations of R. unicolor occur at dusk around regularly used water sources (Eisenburg and Lockhart 1972). During feeding trials, forage intake by captive R. unicolor in India decreased from about 400 bites/day, with ad libitum water, to <200 bites/day after 3 days of water deprivation (Berwick 1974). Related Javan rusa (R. timorensis russa) in captivity in Australia tolerated saline water of 1,000–6,000 mg/kg of total dissolved salts with little effect on food intake, food digestibility, and nitrogen balance, but when salinity reached 8,500 mg/kg, they showed signs of stress such as rapid breathing, head shaking, and swelling of the preorbital gland (Yape Kii and Dryden 2005). R. unicolor occurs near estuaries and ocean coasts (Geist 1998; Whitehead 1972), and it may have a similar tolerance of salty water. In Florida, however, R. unicolor prefers freshwater habitats and avoids saltwater habitats (Flynn et al. 1990), which may reflect preferences for forage growing in such areas rather than intolerance of salt water.

Fig. 6

Mature male Rusa unicolor wallowing in the muddy wetland in Ranthambhore National Park, Rajasthan, northern India; note the acutely angled brow tine, approaching 50% of the main beam. Photograph by Chris Brunskill ( www.ardea.com) used with permission.

Mineral licks are used regularly by R. unicolor (Brander 1923; Matsubayashi et al. 2007a; Schaller 1967), particularly at night (Matsubayashi et al. 2007b; Peacock 1933). In tropical rain forests of Borneo, lactating female R. unicolor use natural mineral licks more frequently during the wet season than the dry season, and both sexes visit such licks more often at night (85% of visits) than during daylight (15% of visits—Matsubayashi et al. 2007b). Water associated with mineral licks in Borneo provides substantially more macronutrients (mean ± SD, µg/ml ) than control water from local ponds and streams: calcium, 83.4 ± 50.0 versus 13.8 ± 8.5; magnesium, 21.4 ± 9.8 versus 2.7 ± 1.0; potassium, 14.4 ± 12.6 versus 1.6 ± 0.6; and sodium, 801.8 ± 1,173.5 versus 6.9 ± 2.4 (Matsubayashi et al. 2007a).

Diseases and parasites

No infectious diseases or disease agents have been reported to cause substantial population declines of Rusa unicolor (Presidente 1978, 1984a, 1984b; Slee 1984), but foot-and-mouth disease in Sri Lanka (Brooksby 1973) and India (37 of 104 individuals affected—Barman et al. 1999), sarcocystotic cysts with associated pathology of a bluetonguelike disease in India (Acharjyo and Rao 1988; Gangadharan et al. 1992), erythrocyte sickling in Borneo (Dunn 1964; Undritz et al. 1960), and mucosal disease virus, malignant catarrhal fever, and, rarely, infectious bovine rhinotracheitis in Australia (Presidente 1984a; Slee 1984; Slee and Presidente 1981) have been reported. Diseases, or disease-related deaths, have been reported in captive individuals: chronic (erosive) arthritis, tuberculosis, and arteriosclerosis (Fox 1939); foot-and-mouth disease (Kar et al. 1983; Presidente 1984a; Sarma et al. 1983); malignant catarrhal fever (Semiadi et al. 1994b); and bovine tubercule bacilli (Datta 1954). Intestinal rupture and resulting acute peritonitis, perhaps from a parasitic infection, was reported in a wild pregnant female R. unicolor in India (Bhattacharjee 1986).

By the mid-1980s, 18 endoparasites (9 nematode species, 6 flukes, 2 protozoans, and 1 tapeworm) and 40 ectoparasites (35 tick species, 2 sucking lice, 2 keds, and 1 flea) had been reported in native, feral, and captive populations of R. unicolor (Presidente 1984a). Parasites of free-ranging R. unicolor in native habitat include the nematodes Bunostomum, Haemonchus, Oesophagostonmum, Strongyloides, and Trichuris in India (Bhat and Manickam 1998; Hiregoudar 1976) and Ashwortius sidemi, Rinadia andreevae, and Spiculopteragia houdemeri in Vietnam (Drozdz 1965, 1973), and trematodes Calicophoron microbothrioides in Malaysia (Lee et al. 1987), and Fischoederius elongates, Homologaster poloniae, Paramphistomum explanatum (Patnaik and Acharjyo 1970; Rao and Acharjyo 1969), and Gastrothylax crumenifer in India (Agrawal and Ahluwalia 1980). Feral and captive populations of R. unicolor also harbor a variety of internal parasites including nematodes Gongylonema pulchrum (Chakrborty 1994) and cestode cysts Coenurus gaigeri (Varma et al. 1994) in India; Spiculopteragia asymmetrica in New Zealand (Andrews 1973) and Australia (Presidente 1984a); trematodes Ceylonocotyle streptocoelium in Australia (Keith and Keith 1969) and Paramphistomum explanatum in India (Rao and Acharjyo 1984); and protozoans Theileria aristotelis (Levine 1971) and Toxoplasma gondii in India (Ippen et al. 1981).

External parasites of native and feral R. unicolor include ticks Haemaphysalis ramachandrai and H. davisi in India and Nepal (Dhanda et al. 1970; Hoogstraal et al. 1970); H. anomala and H. papuana in southeastern Asia (Hoogstraal et al. 1965, 1967); H. davisi in Malaysia (Hoogstraal and El Kammah 1971); H. mjoebergi in Borneo and Sumatra (Hoogstraal and Wassef 1982); and Dermacentor variabilis in Florida (Davidson et al. 1987). Captive R. unicolor in eastern India, and no doubt wild populations elsewhere, are affected by the hematophagous flies (Tabanus rubidus, T. striatus, Stomoxys calcitrans, Haematobia irritans exigua, and Musca crassriostris) that can transmit trypanosomiasis and other diseases (Veer et al. 2002). When flying parasites are most active (e.g., humid, rainy seasons), larger than normal groups of R. unicolor are seen often in open areas and near or submerged in water (Prater 1980).

Interspecific interactions

Because of the extensive native range of Rusa unicolor in southern Asia (Fig. 3), it can be sympatric with many other large herbivores (e.g., Schaller 1967), with which competitive interactions for food may exist (Sankar et al. 2007). In India, for example, R. unicolor can be sympatric with axis deer or chital (Axis axis), hog deer (A. porcinus), barasingha (Rucervus duvaucelii), red muntjac (Muntiacus muntjak—Kushwaha et al. 2004), blackbuck (Antilope cervicapra), chinkara (Gazella bennettii), chowsingha (Tetracerus quadricornis—Leslie and Sharma 2009), nilgai (Boselaphus tragocamelus—Leslie 2008), gaur (Bos gaurus), water buffalo (Bubalus bubalis—Berwick 1974; Jathanna et al. 2003; Karanth and Sunquist 1992), Asian elephants (Elephas maximus—Shoshani and Eisenberg 1982), and Indian rhinoceroses (Rhinoceros unicornis—Laurie et al. 1983). Significant dietary overlap of R. unicolor and livestock can occur locally (e.g., Shukla and Khare 1998; Srivastava et al. 1996). In extreme eastern Asia and Taiwan, R. unicolor can be sympatric with the smaller sika deer (Cervus nippon—Feldhammer 1980; MacKinnon 2008). In southern China, the distributional range of R. unicolor could overlap with red deer, forest musk deer (Moschus berezovskii), tufted deer (Elaphodus cephalophus), red muntjac, Reeves' muntjac (M. reevesi), Chinese water deer (Hydropotes inermis—MacKinnon 2008), and white-lipped deer (P. albirostre—Leslie 2009), but habitat affinities and decimated populations likely limit direct interactions in most areas (Timmins et al. 2008).

Typically, some degree of habitat (Bagchi et al. 2003a, 2003b; Berwick 1974; Dinerstein 1979; Kushwaha et al. 2004) and dietary (Berwick 1974; Khan 1994; Shukla and Khare 1998) differentiation occurs among R. unicolor and other ungulates. In Ranthambhore National Park, India, R. unicolor and chital form a “cervid guild” that prefer Anogeissus–Grewia forests, and nilgai and chinkara form a “bovid guild” and select Acacia–Butea habitats during summer and winter; unlike the cervids, nilgai were tolerant of livestock grazing and associated degradation of grass cover (Bagchi et al. 2003a, 2003b). In contrast, high dietary overlap of 90–93% was noted among R. unicolor, chital, and nilgai in the semiarid Sariska Tiger Reserve, northwestern India (Sankar et al. 2007). In the Himalayas of northern India, R. unicolor is sympatric with Himalayan musk deer (Moschus chrysogaster), serow (Capricornis sumatraensis), and goral (Nemorhaedus goral—Mead 1989); competitive interactions are avoided by inverse relationships of habitat use and diet, but diets of R. unicolor and serow were most similar in autumn (Green 1985, 1987). In Nepal, R. unicolor uses riverine forests (80% of its time) with muntjac (78%) and chital (75%) but not hog deer (<5%—Mishra 1982 [not seen, cited in Putman 1988]). On St. Vincent Island, Florida, R. unicolor and white-tailed deer (Odocoileus virginianus—Smith 1991) partition habitat and food resources; in particular, R. unicolor uses freshwater habitats and associated aquatic vegetation (11.1–56.2% aquatic vegetation in seasonal diets; Figs. 2 and 6) to a much greater extent than white-tailed deer (1.5–4.4%—Shea et al. 1990).

Cattle egrets (Bubulcus ibis; Fig. 7) and Indian, or rufous, tree-pies (Dendrocitta vagabunda) associate with and forage on R. unicolor, respectively. Bharucha (1987) observed a female R. unicolor standing awkwardly with a rear leg raised up and away from her body to accommodate an Indian tree-pie that was apparently removing parasites from her groin area.

Fig. 7

Male Rusa unicolor and cattle egret (Bubulcus ibis) foraging together in wetland in Ranthambhore National Park, Rajasthan, northern India. Photograph by Chris Brunskill ( www.ardea.com) used with permission.

The endangered Indian tiger preys extensively on R. unicolor (Mazák 1981; Ramesh et al. 2009; Schaller 1967; Wang and Macdonald 2009) and, anecdotally, is said to mimic the call of R. unicolor to deceive it while hunting (Whitehead 1972). In Nagarahole, southern India, tigers prey preferentially on male R. unicolor (43 kills: adult males, 40.0%; adult females, 30.6%; yearling males, 5.7%; yearling females, 5.7%; 122 scats: young-of-the-year, 18.0%) and take more young individuals (58.6%) than prime (34.5%) or old (6.9%) individuals (Karanth and Sunquist 1995). R. unicolor constitutes 30.5% of prey items in tiger scats and 36.8% of tiger kills in Bandipur Tiger Reserve, southern India (Johnsingh 1983), and 24.9% and 28.6% in Nagarahole National Park, southern India (Karanth and Sunquist 1995, 2000). Frequency of occurrence of R. unicolor in tiger scats is 59.8% in Mudumalai Tiger Reserve, southern India (Ramesh et al. 2009); 51.4% in Sariska Tiger Reserve, northwestern India (Sankar and Johnsingh 2002); 36.9% in Ranthambhore National Park, northern India (Bagchi et al. 2003b); 14.6% in Pench National Park, central India (Biswas and Sankar 2002); and 27.6% in Nagarjunasagar Srisailam Tiger Reserve, south-central India (Reedy et al. 2004). Seidensticker (1976a) considered R. unicolor a primary prey species of tigers in Royal Chitwan National Park, Nepal, as did Wang and Macdonald (2009) for tigers in Jigme Singye Wangchuck National Park, central Bhutan. The Sumatran tiger (P. t. sumatrae) in Bukit Barisan Selatan National Park, Sumatra, Indonesia, also preys on R. unicolor (O'Brien et al. 2003).

Rusa unicolor, primarily fawns, constitutes 14% of prey items in scats and 5% of the kills of the leopard (Panthera pardus) in Bandipur Tiger Reserve (Johnsingh 1983) and 13.5% and 9.6% in Nagarahole National Park, southern India (Karanth and Sunquist 1995, 2000). In southern India, frequency of occurrence of R. unicolor in leopard scats is 29.0% in Mudumalai Tiger Reserve (Ramesh et al. 2009), 9% and 11.7% on the Mundanthurai Plateau and in the Mudumalai Wildlife Sanctuary, respectively (Ramakrishnan et al. 1999), and 5.9–7.8% in Sigur and Thalamalai reserve forests (Arivazhagan et al. 2007). Scats of leopards in Wolong Reserve, Sichuan, China, have only 0.5–1.6% frequency of occurrence of R. unicolor (Johnson et al. 1993). In Sri Lanka, only 1 of 29 identified prey items of leopards was R. unicolor (Eisenberg and Lockhart 1972). R. unicolor comprised 14.8% of 142 kills by highly endangered Asiatic lions (Panthera leo persica—Haas et al. 2005) in Gir Forest, India (Berwick 1974; Chellam and Johnsingh 1993).

Frequency of R. unicolor in scats of the group-hunting dhole (Cuon alpinus—Cohen 1978; Earle 1987) was 14.7% in Mudumalai Wildlife Sanctuary in southern India (Cohen et al. 1978), and elsewhere in India, comprised 9–15% of the dhole diet (Arivazhagan et al. 2007). In Bandipur Tiger Reserve, fawns of R. unicolor (31.4%) were about 3 times as frequent in dhole scats as adults (10.6%—Johnsingh 1983). In Nagarahole National Park, southern India, 10.2% of prey items in dhole scats and 3.0% of prey kills were R. unicolor (Karanth and Sunquist 1995, 2000). Composite samples of scats from large carnivores, primarily dhole and leopards, in Huai Kha Khaeng Wildlife Sanctuary, Thailand, contained only 1.2–6.4% R. unicolor (Rabinowitz and Walker 1991). In Khao Yai National Park, Thailand, R. unicolor was the most common prey found in dhole scats (Austin 2002). The highest reported frequency of occurrence of R. unicolor in dhole scats was 60.9% in in Jigme Singye Wangchuck National Park, central Bhutan (Wang and Macdonald 2009).

In India, R. unicolor has not been reported as prey of the endangered Indian wolf (Canis lupus pallipes) or the striped hyenas (Hyaena hyaena—Arivazhagan et al. 2007), as have other species (Leslie 2008). Green (1985) found small amounts of hair of R. unicolor in scats of red fox (Vulpes vulpes) in Kedernath Sanctuary in the Indian Himalayas, believed to be from fawns or scavenged animals.

Grouping behavior

Kurt (1978:233) described the social and reproductive systems of Rusa unicolor as varying, depending on habitat, from “non-seasonal, alternatingly territorial” in stable rain forest to “seasonal, synchronized territorial” in varied deciduous forest and “solitary, aggregational” in stable grass jungles. Unlike most comparably sized cervids characterized by large groups (Geist 1998), R. unicolor typically occurs in small groups, most often a single female that dominates the group, her young-of-the-year, and perhaps her female yearling; mature males > 6 years old are typically solitary, with young males grouping together, close to females, or as satellites to solitary mature males (Eisenberg and Lockhart 1972; Khan et al. 1995; Schaller 1967). In some areas (e.g., Sri Lanka—Kurt 1978), R. unicolor occurs with regularity in groups of 30–40, usually related to more abundant patches of forage and water availability (Geist 1998).

Maximum group size of R. unicolor in Gir National Forest, western India, was 5 individuals (Berwick 1974), and in Gir Lion Sanctuary, there were no seasonal differences in group size (Khan et al. 1995). Group sizes were 1–10 individuals in Nagarahole, southern India: 52% of the groups, 1 individual; 44%, 2 or 3 individuals; and 4%, 4–10 individuals (Karanth and Sunquist 1992). Group sizes were 1–16 individuals in Bandipur Tiger Reserve, southeastern India: 39% of the groups, 1 individual; 27%, 2 individuals; 21%, 3 or 4 individuals; 7%, 5 or 6 individuals; 3%, 7–9 individuals; 3%, 10–16 individuals (Johnsingh 1983:figure 6). In Mudumalai Wildlife Sanctuary, southern India, group size averaged 3.1 individuals but varied seasonally: maximum dry-season group size was 19 individuals and maximum wet-season group size during 2 years was 44 and 50 individuals (Varman and Sukumar 1993). Mean summer and winter group sizes in Ranthambhore Tiger Reserve, India, were 4.2 and 3.4 individuals, respectively (Bagchi et al. 2008). In Sri Lanka, group size was 2–8 individuals, and 60% of 230 individuals were solitary (Eisenberg and Lockhart 1972). Group size is often largest near water holes (Johnsingh 1980, 1983).

Reproductive behavior

Downes (1983b:36) described the mating system of Rusa unicolor as “polygamous male dominance … in dispersed facultative meeting-territories.” Reproductive behavior of R. unicolor is “primitive with unique elements” (Geist 1998:76); males do not establish harems (Brander 1923; Schaller 1967). At the beginning of the breeding season, male and female R. unicolor “suddenly [begin] to wander widely, even at mid-day, becoming highly conspicuous in sharp contrast to their usual elusiveness,” and appear “nervous, as if looking for something” (Schaller 1967:144).

The following description of reproductive behavior was synthesized from Brander (1923), Downes (1983b), Fletcher (1911), Geist (1998), Prater (1980), Schaller (1967), and Thom (1937). During rut, mature males establish nonexclusive breeding territories to attract females and from which they challenge competitors of comparable rank; younger males often occupy peripheries of such territories. Mature males in rut have swollen necks, strong odor, and everted preorbital glands and appear aggressive, often thrashing vegetation. They are usually coated with mud from regular wallowing in wet spots (Fig. 6), accentuating their generally dark pelage, and frequently rub their muddy necks on tree trunks and vegetation while patrolling their territories for receptive females and competing males. Females are said to wallow but less frequently than males (Peacock 1933). Males paw and stomp the ground, and thereby create areas as large as 3–13 m in diameter, devoid of vegetation; “stomping grounds” may occur in dense forest or in the open atop hills. Often such areas are below an overhanging branch 2.3–3.3 m off the ground; male “preach” at these sites by standing erect on their hind legs and rubbing their scent-soaked preorbital glands and antlers on the branch (a behavior not observed among introduced R. unicolor in Florida). Males copiously spray themselves, even their faces, with urine from their mobile penis, the structure of which is unique among cervids.

Aggressive behavior between competing males includes head-up and head-down displays, pawing and thrashing, and head-to-head pushing matches, with tail cocked up and mane and back hairs erected, until the weaker gives up. Geist (1998:76) noted that, unlike any other deer species but goat-like, male R. unicolor will “rise on their hind legs and clash downward into one another.” Females also rise on their hind legs and hit each other on the head with their forelegs, resulting in a “noise [that] resounds through the jungle;” the same behavior is used against predators (Brander 1923:177).

Sexual behavior of R. unicolor has not been described in detail, but accounts by Brander (1923), Geist (1998), and Schaller (1967) provide some insight. Females actively seek or court adult males, moving widely among breeding territories; courtship is based on pair-bonding without serious vocal advertisement; males do not clasp females during mounting, front legs hang loosely (Fig. 8); and intromission is a “copulatory jump” (Geist 1998:76). Schaller (1967) observed mature males sniffing and licking females' vulvae. Another male trotted after a female in a low-stretch display with his neck parallel to the ground and preorbital glands everted. Satellite males assist dominant males by “warding off lesser rivals” and may breed if >1 receptive female enters the dominant male's territory (Geist 1998:77).

Fig. 8

Mature male Rusa unicolor mounting a female in Ranthambhore National Park, Rajasthan, northern India, January–February 2000. Photograph courtesy of James Warwick ( www.jameswarwick.co.uk) used with permission.

No published observations of parturition of wild R. unicolor were found. Presumably, females separate themselves from other individuals, seek secluded places to give birth, and hide their neonates. Neonates may rest alone, hidden, for much of their first 3 months of life, with their mother returning at regular intervals (Eisenberg and Lockhart 1972; Shea et al. 1990).

Communication

Brander (1923) noted that eyesight of Rusa unicolor was only moderately developed, but Peacock (1933) contended that all senses were highly developed. Along with highly developed scent-marking routines and persistent acrid odor, particularly among males in rut (see “Reproductive behavior”), foot stomping by female R. unicolor is used to alert (and summon) neonates and conspecifics of threats (Brander 1923; Mason 1994). Despite their size, R. unicolor can move quietly (Stebbing 1911) and with stealth through dense forest; mature males, when moving rapidly “enclose their necks and shoulders” with their antlers by “carrying their heads thrust out before them” (Brander 1923:182). Ever alert and a “high-stepper” stomping its forelegs when alarmed (Stebbing 1911:59), R. unicolor makes “sharp, short ‘pooks,’” “tits,” or “honks” ( =  “sharp, high notes”) when disturbed (Brander 1923:180; Lydekker 1916; Mason 1994:23; Peacock 1933:126; Thom 1937). Brander (1923:180–181) described 2 other call types: a “loud metallic bellow” of rutting males and a “death cry” consisting of “a prolonged hoarse scream.”

Miscellaneous behavior

Rusa unicolor is largely crepuscular to nocturnal depending on location (Brander 1923; Fletcher 1911; Peacock 1933), but it can be active throughout the day in areas with minimal human disturbance (Johnsingh 1983; O'Brien et al. 2003) and in introduced locations such as Texas (Richardson 1972). Anecdotally, the Malayan form may be more nocturnal than Indian forms (Evans 1912), but Peacock (1933:125) described R. unicolor in Burma as “very nocturnal … ordinarily seek[ing] heavy cover with the first light at dawn and not leave[ing] the same till dusk.” U Tun Yin (1967) contended that nocturnal habits of R. unicolor in Burma were related to continual human harassment.

Much like the moose (Alces alces—Franzmann 1981), R. unicolor is 1 of the few deer that will readily face wild predators (e.g., leopards and dholes) and hunting dogs defensively (Brander 1923; Geist 1998; Johnsingh 1980; U Tun Yin 1967). Females defend their young in a low-head posture, “barking loudly” and stomping front legs, with tail and ears erect and mane hairs flared; if several females are present, they stand rump-to-rump, facing outward toward the threat (Geist 1998:75)—reminiscent of muskoxen (Ovibos moschatus—Lent 1988) and the wild yak (Bos mutus—Leslie and Schaller 2009). If the threat is minimal (e.g., a single dhole), they may not react at all (Divyabhanusinh 1988). Brander (1923) recounted an incident when a female R. unicolor aggressively defended its young from a leopard who successfully carried the offspring 3 m up into a tree; when a hunter arrived on the scene, the leopard dropped the young, which ran off with its mother. Females can be “savage” while protecting their neonates in captivity (Crandall 1964:569). When perceiving or facing a threat, R. unicolor will not typically run off but often stands motionless, its dark pelage blending into the surrounding vegetation; alternately, it may creep off in a “semicrouch trot” with its neck held horizontally (Schaller 1967).

Rusa unicolor readily swims with its body fully submerged and only its head above the water (Prater 1980; Fig. 9), often to avoid insects and to forage (Richardson 1972; Shea et al. 1990; Shukla and Khare 1998). When ambient temperatures approach freezing, R. unicolor may lie in water that is warmer than the air (Brander 1923; Prater 1980).

Fig. 9

Mature male Rusa unicolor swimming through wetland in Ranthambhore National Park, Rajasthan, northern India, January–February 2000. Photograph courtesy of James Warwick ( www.jameswarwick.co.uk) used with permission.