Nestbox grids in population studies of theCommon dormouse (Muscardinus avellanarius L.): methodological aspects

Two different nestbox grids have been used for studies of the common dormouse (Muscardinus avellanarius L.) populations: high-density nestbox grids in small plots (e.g. 25-30 boxes ha^-1 in 1 ha plots) and low-density nestbox grids in large plots (e.g. 4 boxes ha^-1 in areas of 60 and 85 ha). The present study aimed to compare efficiency and suitability of 25 x 25 m and 50 x 50 m nestbox grids for studies of the common dormouse population, and to show limitations of small study plots in dormouse studies. Live trapping of dormice within nestbox grids proved that all dormice captured used nestboxes placed in both 25 x 25 m and 50 x 50 m grids. Regular control of nestboxes placed in the 25 x 25 m grid gave an opportunity to register all adult dormice living in the study site during shorter periods, and average dormouse capture rate was significantly higher compared to the 50 x 50 m grid. However the 25 x 25 m nestbox grid had one substantial drawback: high nestbox density (16 boxes ha^-1) increased environment carrying capacity for dormice in the forest, where natural hollows were almost absent. In consequence, adult dormouse density increased two to four-fold, while their home range sizes decreased by about half. Dormice are distributed irregularly in large forest areas, and the results obtained in small study plots may not reflect the average characteristics of the population. Some results obtained in small study plots (e.g. density, mortality) can be overestimated because of dormouse movements and edge effects. Predators, e.g. owls, can catch some dormice and substantially influence the results obtained in small plots. Because of the influence on dormouse population density and other population parameters, high density nestbox grids (e.g. 20 x 20 m, 25 x 25 m) should not be used in dormouse population studies. Small study plots (e.g. 1 ha) are completely unsuitable for estimation of such dormouse population characteristics as survival (mortality) and dispersal.