BURROWS, LODGES AND HOME RANGES OF THE MUSKRAT, ONDATRA ZIBETHICA LINNE

The present study deals with the construction, types and some of the biological characteristics of muskrat's houses. At the same time, the relation between their homes and home ranges has also been discussed. However, stress has been laid on the phenomena concerning the limiting factor of space rather than on the absolute values for the latter item. The data herein enclosed were obtained as part of the study of the ecology of the muskrat in five provinces of China during 1960-1961. The results of the study are as follows:(1) The home of a muskrat consists of burrows, lodges, channels, shelter passageways and feeding ground. According to their constructions, burrows and lodges can be classified into two types, simple and complex. Besides, the complex form of burrows is again divisible in to two forms, namely, individual and familiar, due to their use. (2) The situations of the burrows and lodges seem to be closely related to the micro-relief of habitat of the muskrat. The burrows tend to be situated in the high form of bank along shores. The lodges are usually built at the shallow water zone. (3) The height of burrow systems averaged 43.4 ± 19.23 cm. The lengths from ground surface to the upper levels of the simple, individual and familiar burrows averaged 21.17 - 10.71, 15. ± 4.65, 11.38± 6.23 cm. respectively; the greatest no more than 45 cm. The length between nest sites and ground surface was found to be 21.1 -12.01 cm. The position of entrances to lodges and bank burrows is changed in accordance with the fluctuations of the water level. But when the water level seems to have risen greater than the height of burrow systems and lodges, a house in that situation cannot hold its inhabitants. If the water level no more reaches the height of houses, the occupancy of the houses may also be affected when the water level rises too quickly, and therefore many animals should simply depart. (4) There seems to be very little correlation between the arrangement and structure of burrow systems and the physical property of the soil. (5) The temperatures in the burrows and lodges were recorded as 14-15℃ from April to November in the various regions of China. Temperature far above 34-36℃ about two hours under sunshine would cause the muskrat a sudden death. So the relative stability of temperature in houses would play an important role in their life. (6) The muskrat houses usually consist of two or more burrows and lodges, which may be considered as a house-group. The proportion between the numbers of the main and the accessory burrows or lodges and their arrangements did not appear to be definitely set. The house-group is characterized in their arrangement by two very distinctive forms, namely, aggregated and dispersed. The length of house-group (the distance of farthest burrows or lodges within a house-group) of these two forms measured from 0.40-86 m, the range of which seemed to vary widely; but the length of the central region of the houses appeared to be limited within 6.8 ± 5.19 meters. The house-groups did not hold a definite location in the home ranges. There was no relationship between the length of house-group and the length of the central region of house sites and the home range sizes. Under the conditions of high population densities, the central region of house sites tend to be a limiting factor of space. (7) The home range sizes of muskrat fimilies in seven areas studied averaged 3900, 53.9, 1050.4, 682.7, 153.7, 355.74, 1607.2 sq. m. , which was obtained by field observation and was calculated by minimum area method. From the results of the present study, it is obvious that there was no direct correlation between environmental conditions and home range sizes. Of the 60 families observed in the areas studied, the percentage of the overlapping areas of the home ranges was 75%. The total number of the overlapping areas of the home ranges was recorded as 125. There was one home range which shared with seven families. In general, the overlapping area was found to be 41.36% of their home range. It seemed, therefore, evident