Trophic relationships of the common vole in cultivated fields

Abstract

On the area of 3,100 ha of cultivated fields the density of the following species of rodents was estimated: M. arvalis in fields and C. glareolus, A. flavicollis and A. agrarius in woods. At the same time the numbers of predatory nammals and birds were estimated. During the whole period of study in area under examination 3,400,000 individuals of M. arvalis and 43,000 of forest rodents were present. Between the depression and the peak of numbers the density of M. arvalis increased over one hundred-times. At the density of 44 individuals/ha the voles consumed in a year 79 kg d.w. of alfa-alfa/ha, and at 774 indiv./ha as much as 1,153 kg d.w./ha. It was demonstrated that the ratio of plant weight destroyed to consumed amounted in alfa-alfa cultures to 1.8:1. At a low density c\f M. arvalis considerable losses of winter rye during winter are compensated by the regrowth of plants in spring. Food requirement of predators was determined and their diet in field conditions was investigated. The highest number of M. arvalis was consumed by foxes, lower by cats and weasels. The predators hunted mainly in areas showing the highest rodent density. With the increased numbers of M. arvalis its share in the diet of all predators rose up to 80%. Despite this the pressure of predators on the population of M. arvalis decreased, e.g. in the year of outbreak the predators removed barely 10.8% of all present individuals. With the increased proportion of M. arvalis in the diet of fox the proportion of consumed hares decreases. A scheme of trophic relationships of M. arvalis is presented.