Photograph by William Rainey
This article was inspired by McMorris and Burns' 1975 paper on the impressed tortoise. They focused on the problem of "impressa disease", setting forth the frustrations and difficulties which continue to plague attempts to maintain the impressed tortoise in captivity. The goal of this paper is to share what is known of this species' natural history and to help assure the survival of impressed tortoises in captivity. Recent limited achievements in captive husbandry are summarized, as are observations made by Peter Paul van Dijk and local colleagues on M. impressa habitat in Thailand. As many works as possible dealing with M. impressa published since 1975 have been consulted in this synopsis.
The impressed tortoise, Manouria impressa, was first described as "Geoemyda impressa" by Günther in 1882. The type locality was given simply as "Siam" (Thailand). Research by Obst (1983) traces the origin of the type specimen (CL 225 mm) no further than the Bangkok pet trade. Gray, recognizing the uniqueness of the earlier described Asian brown tortoise M. emys (the closest relative of the impressed tortoise), erected the genus Manouria in 1852. For more detailed accounts of the nomenclatural history of modern tortoise species, see Bour (1980) and Crumly (1988).
Although similar in appearance to a half-grown specimen of Manouria emys, M. impressa is clearly distinct from either subspecies of Asian brown tortoise. Wirot (1979) states that this species does not exceed a carapace length of 28 cm, though Moll (1989) records 31 cm as a maximum. The impressed tortoise is more flattened than the Asian brown tortoise, with characteristically concave carapace scutes from which the common and scientific names are derived. Manouria e. emys has less pronounced carapacial scute concavity. The strongly serrated marginal scutes, and contiguous pectoral plates which always meet at midline are further important characteristics. A single, large conical spur is present on each thigh, in contrast to the cluster of such spurs in M. emys. One colloquial Vietnamese name for the impressed tortoise, rúa sen, translates literally as "three [tailed] tortoise." Males have a distinctive caudal spur clearly visible in Boulenger's 1903 illustration. The caudal spur is absent in M. emys.
The carapace of M. impressa is horn colored to dull orange, with dark, often confluent flecks near the edges of the carapacial scutes. The limbs, clad in large overlapping scales, and other extremities are very dark although the snout is pale, particularly in females. The pale yellow plastron also bears peripheral radiating dark markings in each plate. These contrasting markings fade with age, and large adults may be of a nearly uniform horn color. There are reports that impressed tortoises of any size from Malaysia, on the other hand, are rather drab and of a uniform brownish-yellow. Taylor (1970) considered this species the most handsome of all chelonians indigenous to Thailand, though his figure of a data-less Chulalongkorn Museum specimen showed a young tortoise with an unmarked carapace. Males are distinguished from females not only by the caudal spur and by their darker as opposed to yellowish head and neck, but also by a longer tail.
The geographical distribution of the impressed tortoise was known about as well sixty years ago as it is today. Smith (1931), using now dated geographical terminology, gives the range of this species as 'Burma (Myanmar) (Karenni Hills); Siam (Thailand); Annam (Langbian Plateau); Tonkin; the Malay Peninsula." M. impressa was first recorded from China in 1974 based on a specimen purchased from an animal dealer on Hainan Island. A specimen, almost certainly introduced, was found on the outskirts of Shaoyang in Hunan Province in 1986, and Ermi Zhao reported this species from extreme southern Yunnan Province (Buskirk, 1989). Moll (1989) shows 12 localities in Myanmar, Thailand, Vietnam, and Malaysia, whereas Iverson (1992) includes the Hainan specimen by showing a dot for Haikou--the largest city on the island--but omits other mainland Chinese localities. He does show question marks for western Yunnan and eastern Thailand, and provides an additional locality in extreme southeastern Myanmar.
The natural history of this tortoise is poorly known, but there is some consensus that it is an upland form. Smith (1931) says only that the species occurs "in the hills at considerable altitudes." Boulenger (1903) cites two specimens collected at "1000 feet to 2000 feet" from what is now Perak Province, Malaysia, and two others collected in Myanmar at 3200' and 4000' elevations. He quotes a field observation by Annandale and Robinson as follows: "The two specimens of Testudo pseudemys were taken on a jungle path at dusk, within a few yards of one another. When alarmed they drew in their heads, but when lifted from the ground became very vicious, hissing, stretching out their necks and attempting vigorously to bite, their whole demeanor differing from that of specimens of T. emys I have seen in captivity in the Malay Peninsula."
McMorris and Burns (1975) surmise from exporters' accounts that the "natural habitat for impressa seems to be fairly dry." Wirot (1979) claimed that this species inhabits "forests and mountainous areas," and feeds on "plants and bamboo shoots, and forages in dense undergrowths at an altitude of 700 to 2,000 feet. During the rainy season, it wanders around eating grass shoots and looking for a mate." As "grass" and "bamboo" are the same word in Thai, the exact foodstuff in question is uncertain; perhaps impressed tortoises consume both. Bourret (1939) reports the species as fairly common in a mountainous region of northern Vietnam. Weissinger (1987) reported the impressed tortoise in "inaccessible mountain forests and bamboo thickets" where it is active "only during the rainy season," a period generally not exceeding four months (Pearce and Smith, 1990).
More detailed habitat information is supplied by Nabhitabhata (1991). He concurs with McMorris and Burns (1975) in declaring the habitat to be "fairly dry and generally away from the water bodies, so this tortoise relies instead on dew or rain-drenched vegetation." The same author cites the altitude parameters as 700-2,000 meters, both considerably higher than those figures as reported in feet by Wirot (1979). In an area of broad-leaf evergreen forest in northern-northeastern Thailand visited by van Dijk (personal communication), the leaf litter substrate consisted of a complex mosaic of both wet but mostly dry areas on a flat-topped limestone mountain complex, with no running water available during the dry season (February). This area is reported as typical M. impressa habitat, and is far from "inaccessible" despite Weissinger's (1987) assertion. Montane broad-leaved evergreen forest, sometimes called hill evergreen, occurs between 1,500 and 2,000 m elevation in Thailand. It includes temperate zone trees such as laurels, oaks, and chestnuts, as well as moss, ferns, rhododendrons, and numerous epiphytes (Gray et al., 1991). The exact preferred microhabitat of M. impressa is not yet documented.
Detailed gross climatic information for Chiang Mai (sometimes written Chiengmai or Chingmai) is provided in table 1. This rapidly growing city at an elevation of approximately 2000 feet lies within the historical range of M. impressa and is the site for one locality record. Chiang Mai receives an average of 42" (105 cm) of annual rainfall. Other areas at higher elevation probably inhabited by M. impressa may receive nearly twice as much annual rainfall (Gray et al, 1991). Monthly precipitation in Chiang Mai reaches a maximum of nearly 25 cm (9.8") in September, a month preceded by three of limited sunshine owing to cloud cover and rain. Twelve to 20 days of rain (less than .04"/day) per month are recorded between May and September. Early morning average humidity, higher in other months, is not known to fall below 88% in the late dry season (March and April). Average daily high temperatures of 97°F (36°C) coincide with this same season. Midday relative humidity is highly variable. Overnight drops in temperature by as much as 15°C result in heavy pre-dawn condensation. The mildest weather, with greatest number of hours of sunshine, occurs as the rainy season tapers off in October and November. The lowest daily temperatures (56-59°F, 14-15°C) occur between December and February, following a sharp drop during November. Other species of land tortoise in the region (M. emys, Indotestudo elongata) occur at lower altitudes than those reported for M. impressa.
Weissinger (1987) echoes McMorris and Burns (1975) in documenting the delicate nature of the single specimen that he kept as a captive, and refers to a fellow German, M. Reimann, who also kept M. impressa. Their tortoises paced restlessly, indoors or out, and initially refused to eat. Weissinger's male tortoise developed severe stomatitis successfully treated with debridement and a topical antibiotic. Eventually, after a period of being force-fed, the tortoise consumed "three bananas per week." The ultimate captive longevity of this specimen is not known. McMorris and Burns (1975) list bananas, purple grapes, dates, pineapple-guavas, cucumber, romaine lettuce, wandering Jew, ivy, grass, and "fleshy green plants" as having been consumed by an unspecified number of captive impressed tortoises, all but a few of which died within a few months of having been purchased in Bangkok. Most of the impressed tortoises refused food entirely during their captivity.
Other reports of captive feeding experiences are varied. Reportedly, a specimen imported to the Midwest in the 1970s fed selectively, and only at daybreak, beneath a drizzle of simulated rain from an outdoor faucet. A 20-cm male which survived for ten months (1987-88) in the second author's care was observed feeding on only three occasions: once, exactly a month after acquisition, it took several bites from a growing Dracena plant, and the following day consumed about three leaves from a young spinach plant also growing in the outdoor enclosure. Months later it also consumed part of a growing Dracena leaf. This Thai specimen, an unexpected legal gift from a traveler to that country, appeared vigorous upon arrival in the United States and weighed 1402 g. It frequently drank, especially during real or simulated rain, and even attempted to copulate with a slightly smaller juvenile Manouria emys phayrei, the only other tortoise in the enclosure. The tortoise was treated empirically with both Flagyl and Tramizol, and its occasional stool was found to be free of parasites six months after this treatment. Despite prolonged fasting, the tortoise lost only about 100 g of mass before expiring in late April 1988.