Preliminary observations on the structure of the tunnel system of the Chinese bamboo rat (Rhizomys sinensis) Xiaorui He Department of Biology, Yunnan University Acta Theriologica Sinica Volume 4, Number 3, Page 196 August, l984 Translated by Will Downs Bilby Research Center Northern Arizona University November, 1987 Rhizomys sinensis Thomas, 1921, is extensively distributed in Yunnan Province. It gnaws bamboo shoots, roots, and stalks on a large scale making it the principle damaging rodent in a bamboo forest. From l975 to June 1983, the author of this text has made preliminary observations on the burrowing network of the Chinese bamboo rat in the outskirts of the City of Kunming, in addition to the counties of Xinping, Yuanyang, Honghe, and Suijiang in the Ailao Mountains of Yunnan Province. A brief report is as follows: Environment The Ailao Mountains are the southern extension of the Hengduan mountain range that is oriented north-south with the Yuanjiang River flowing southward along the eastern flank. Maximum altitude is 3138 m, and minimum altitude is 300 m. Rhizomys sinensis is predominantly distributed in bamboo and broad leaf evergreen forests between the elevations of 1500 and 2800 m. Above 2000 m the flora is represented predominantly by primeval forest. Bamboo forests are principally composed of Sinarundinia sp. and S. nitida.. Here the habitat is tropical to subtropical with the river valley regions under sweltering conditions. The annual mean temperature is 18° C. Above 2500 m, however, the climate is temperate and precipitation is over 1100 mm. Bamboo rats construct their burrows mostly on the slopes of broadleaf and bamboo forests with a slope angle generally of 30°-50°. Adult bamboo rats maintain individual burrow networks. Earth mounds and tunnel entrances During the process of excavating its burrows, Rhizomys sinensis thrusts up an extreme amount of soil, which upon the surface is formed in the shape of mounds, beneath which are the tunnels. The authors were able to diagnose the presence of bamboo rats in the subsurface even though an open burrow entrance was absent based upon the presence of spongy mounds in bamboo groves which lacked an appreciable amount of deciduous or bamboo leaves covering them and lacked long bryophytes or lichens upon them. It is determined that the length of time the rodent inhabits a single burrow system is generally less than one year, but occasionally reaches 5-6 years. This is based upon the analysis of remnant bamboo nodes within the burrows (degree of bamboo decomposition). As the length of habitation increases the quantity of mounds increase. One system is documented with a 14-tunnel network with each tunnel maintaining 4-7 individual chambers. These are nearly conical in shape with a diameter of 50-80 cm and a height of 20-40 cm. When there is an inhabitant of the burrow system, the tunnel entrance is sealed and completely covered by an earth mound. Only during mating season under a monogamous system is the burrow entrance opened for a short duration. On June 20, 1982, the author excavated a mound in Xinping Co. exposing the tunnel entrance. The next day at a 9 o'clock observation the inhabitant had re-excavated earth to cover the tunnel entrance. Foraging Tunnels Foraging tunnels are the feeding and livelihood passages for Rhizomys sinensis. The animal gnaws a tunnel, taking the surrounding bamboo roots, the unsprouted bamboo shoots, and bamboo plants by dragging them down into the tunnels and biting off a small section to be later gnawed upon at leisure. The foraging tunnels bifurcate and run parallel to the surface of the ground 20-30 cm beneath the surface, commonly with 4-7 bifurcations. As the number of bifurcations increase, the lengths of the tunnels also increase, indicating a longer period of habitation. The breadth of these tunnels is 17-23 cm and height is 16-22 cm. In the 14-tunnel system, the lengths of the foraging tunnels generally range from 11 to 44.5 m, with an average length of 31.2 m. The interior of the tunnels is relatively arid and lacks accumulated water. 2 The depth of the foraging tunnel is intimately related to the depth of the bamboo roots. A dissection of tunnel network #4 documents that from the surface of the ground to a 14 cm depth there is a humus zone; from 14-60 cm is the principle root zone of bamboo, with the roots in interlocking coils; from 60-130 cm is the fibrous root zone of bamboo, and from 130 cm downward is rootless except for those belonging to other shrubs and trees. The foraging tunnels occupy the principle root zone of bamboo above which are only bamboo stalks. The interiors of the foraging tunnels are relatively smooth. There is a distinction between new and old foraging tunnels as the new tunnels follow the main roots of bamboo growing either in the current year or in recent months. The feeding channels either one or several years older display interiors that are less smooth than the former. Some of the tunnels lie unused for many years and thus are obstructed and have been abandoned. The Den The den is the dwelling area, birthing chamber and location for raising the litter. It is generally excavated above the foraging tunnels, situated 30-60 cm from the earth mounds, and very near the refuge tunnel, being only 50 cm away. The diameter of the den is 22-25 cm and it is 20-23 cm high, being distinctly broader than the feeding channel. The floor of the den mat is composed of a number of gnawed bamboo twigs with lengths of 10-23 cm, diameters of 1.1-1.7 cm, and generally represented by 8-10 pieces. Above this are spread numerous bamboo threads, roots, branches, leaves, and thin tree roots. The bamboo rat does not have an obvious regular toilet and defecates 3-10 cm from the edge of the den. Its excrement is green, elliptical in shape, pellet length 1.3-3 cm, 0.7-1.4 cm in breadth, relatively solid, and basically odorless. When there is difficulty obtaining food, or the food resources in the vicinity of the den have been exhausted, the occupant opens a new separate tunnel lateral to the foraging tunnel, or continues forward depending on its convenience. At this time, the previous den is abandoned and a new one constructed. One tunnel system may contain 4-10 individual dens with 1-3 recent dens and 3-7 old dens. Refuge Tunnels The refuge tunnel is the sanctuary for fleeing from the pursuit of enemies and danger. In May-June of 1982 and May of 1983, the author excavated a tunnel system to discover that the den was warm, which indicated the inhabitant does not ordinarily reside in the refuge tunnel. Upon noticing the cold from the excavation, the inhabitant rapidly fled into the refuge chamber. Consequently, the authors captured the bamboo rat intact within this chamber. The refuge tunnel is 3.5-13.5 m in length (average as 6.43 m) and 1.5-3.5 from the surface (average as 2.13 m). An aged individual maintains a longer refuge tunnel than an immature occupant. The refuge tunnel does not run parallel to the surface of the ground, but trends toward deepening. On a 45° slope, the tunnel direction may be represented in four configurations: horizontal, trending upwards, downwards, or in a sinuous configuration. 3 Figure 1. Rhizomys sinensis #2 tunnel system (left) and #4 tunnel system (right) (with the exception of the refuge tunnels, the remaining are all foraging tunnels.
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