Preliminary observations on the by fjhuangjun


									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:


        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

       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

       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.

         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.

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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