We examined the reliability of laboratory-derived calibration curves for age determination of field individuals of the common vole, Microtus arvalis. The sex-specific calibration curves for age determination based on the relationship between eye lens mass and age derived in the laboratory were applied to a live-trapped field population of common vole. When comparing the individual’s age to the length of its trapping history, we found a slight tendency for underestimation of real age. These errors were observed slightly more in females than in males and in individuals captured over a longer time. This could mean that growth rates in captive animals, especially older ones, and in females are greater than those from the field. The month of first trapping has no effect on the presence of the error. We suggest that, in population studies with a special concern for ageing individuals over the whole life span, other methods should be examined, such as those measuring insoluble eye lens proteins or calibration curves based on more than one predictor.
Succession of weeds and small mammal species was studied and compared on alfalfa field in two periods (cultivated 1996–1998 and set-aside 2001–2003). Composition of the plant community changed between the two periods of study. In the first period high biomass of green alfalfa biomass was available to the common vole which dominated small mammal community (88.7 %) and pronounced variation in maximal autumnal densities, typical of cyclic vole populations. Massive invasion of seed bearing weeds was stated after the field was set-aside and alfalfa biomass lowered. With the succession of weeds other rodent species such as Apodemus sp. increase their relative abundance (RA) and that of the pygmy field mouse was higher in the abandoned field compared with the common vole. The trend toward increasing RA was quite distinct (Z = 1.883; P = 0.060). Diversity of herb species and the small mammal species increased with abandonment. The monthly RA of the common vole was, on average, lower in the abandoned field than in the former period (Z = 2.353, P = 0.019). Also the cyclicity disappeared and RA of the population exhibited only seasonal oscillations. Biomass of the small mammal community decreased after the field was set-aside (Z = 3.021, P = 0.002).