PREDICTING DAMAGES OF VOLES IN FOREST CULTIVATIONS

Voles like the Field Vole Microtus agrestis, the Common Vole M. arvali s, the Bank Vole Clethrionomys glareolus and the Water Vole Arvicola t errestris can cause severe damages in forest cultivations by gnawing t he trunks and the roots of the young trees. Damages occur:during winte r time when the population density of these species is high and food r esources are limited. The forecast of the development of vole populati ons is needed to prepare countermeasures against vole damages'. The in crease or decrease of a vole population can be predicted, if the ferti lity of the caught specimens is observed. The gonadal size of the male s was a suitable predictor for the trend of the development of a vole population. The change of population density of the Bank Vole in a tim e interval of 3 month (September-December) was highly correlated (r = 0.86) with the gonadal index of males. The percentage of pregnant or l actating femals was also a good indicator, but less suitable for pract ical use. It is assumed, that the hormones of the hypophysis like FSH, LH and Prolactin rule the growth of the gonads, the fertility and the reproduction in a vole population. Testis size is an indicator for th e activity of these fertility hormones and for the reproductive proces s. It can be used to predict the development of vole populations for a limited time interval.