Renewal of burrows by the common vole as the indicator of its numbers

Abstract

It was attempted to find out whethe r a correlation exists between the numbe r of renewed burrows and numbe r of the common vole Microtus arvalis (Pallas , 1779) since this criterion is used as a relative method of estimaing vole numbers. During two years 6 sampling trials, each lasting one month, wer e carried out on one hectar e lucerne plots. The renewa l of burrows wa s determined in one and two days afte r covering them up, and the numbe r of voles wa s estimated by the CMR method. It was found tha t when all burrows ar e covered u p on a definite plot a correlation exists between the numbe r of renewed openings and numbe r of voles. The accuracy of this relative method of estimating numbers based on the process of burrows renewa l depends on th e are a of the sample and time left for th e renewal: with the increase of sampling are a the value of correlation coefficients increases, and afte r two days higher coefficients wer e found tha t afte r one day. Th e values of correlation coefficients undergo seasonal changes reaching the maximum in August and September. The numbe r of burrows falling for one vole shows considerable seasonal variations and henc e the numbe r of covered burrows cannot corresponds to the numbe r of voles. On the other hand, the numbe r of renewed burrows per one individual has a rathe r constant value (mean 1.8). The error in the estimation of numbers arising from the assumption tha t one renewed burrow corresponds to 1.8 voles amounts to ±50%, and in some cases even to 100%, depending on seasonal changes of vole activity.