Nest box occupancy dynamics by hazel dormice (Muscardinus avellanarius) in central-western Romania

Abstract

The hazel dormouse, Muscardinus avellanarius is a vulnerable and protected species that is challenging to study due to its specific way of life. Limited data on its distribution and population parameters are available for Romania. We collected data regarding species’ biology and ecology in the hilly areas of central-western Romania, within deciduous forests dominated by oak or beech species. We regularly monitored 80 wooden nestboxes, which served as shelter and breeding sites for the species, to assess the seasonal and sex-related variations in nest box usage. The highest occupancy levels were observed during the autumn, with a smaller peak in the spring. Males occupied more nest boxes than females, although the difference was not statistically significant. They also travelled greater distances. Most nest boxes were occupied by a single individual at a time. Recapture rates did not differ significantly between males and females, and most individuals were recaptured only once. Hazel dormice showed a high level of site fidelity, often returning to the same nestbox or one nearby. Interestingly, 14% of the females bred twice a year, which is a lower percentage compared to findings from other studies. Nest box occupancy rates in this region were also lower than those reported in other areas. However, it is important to note that these variations may be attributed to differences in methodology. The occupancy rate declined with the increased presence of the larger species, the fat dormouse Glis glis, which outcompeted the hazel dormouse.