ON THE RELATIVE FATNESS OF THE RED-BACKED VOLE, CLETHRIONOMYS RUTILUS PALLAS
HSIA WU-PINC & SUN CHUNG-LU (institute of Zoology, Academia Sinica)
Relative fatness or coefficient of condition has been widely used in fish biology as an index to illustrate the environmental suitability and to examine the effect of improvements of conditions in fish management. The authors in this paper have tried to introduce this method to mammalogy, using the red-backed vole, Clethrionomys rutilus, as an example. The relative fatness of each animal was calculated by the following formula:K=100W/L3where K stands for the relative fatness, W the weight in grams, L the length of head and body in cms. Data were analysed statistically with respect to the age characteristics, seasonal changes and yearly variations.The voles were classified according to our former standards (寿振黄,夏武平等, 1959) into 4 age groups: juveniles, subadults, adults and old adults. The materials from the year 1956 (table 1) indicated that the adults had higher K values than the other groups; but those from the data of the year 1957 (table 2) did not bear evidence to this. Sexual differences with respect to fatness was not observed.There were seasonal variations with tespect to the relative fatness. The materials from the years 1956-58 (tables 3-5) indicated that the fatness of the voles (K) was highest in spring (April to June) and lowest during the summer (June to August) but increased again with the coming of autumn (September to October) (figs. 1-2).The yearly variations of the relative fatness showed that it had a negative correlation to population density (fig. 3), and that the relative fatness in September might have some significance in ptedicting population fluctuations in the following summer (fig. 4).