Selection of Nest Material and Summer Nest Location by the Hazel Dormouse (Muscardinus avellanarius) in the Bidstrup Forests, Denmark

SIMPLE SUMMARY: The hazel dormouse is a threatened species and knowledge about its ecology is vital for conservation purposes. It constructs summer nests directly in the vegetation, in tree hollows, or in nest boxes. The availability of nest materials and vegetation coverage may affect the likelihood of finding hazel dormice at a location. The aim of this study is: (1) To investigate the preferences of hazel dormice for nesting materials today compared to four decades ago. (2) To investigate hazel dormice preferences for vegetation coverage at nest sites. Beech, grass, and bark are the most important nest materials in both period A: 1980–1985 and period B: 2019–2020, although the nests from period A contained more beech and less oak compared to nests from period B. Therefore, ensuring the availability of these preferred nest materials is important in conservation efforts for the species in Denmark. Coverage of shrubs above 2 m is important for nest site selection. Beech and high understorey (2–8 m) may be crucial in the conservation management of hazel dormice in Denmark. ABSTRACT: Hazel dormice (Muscardinus avellanarius) construct summer nests for resting and breeding. The nests are built directly in the vegetation, in tree hollows, or in nest boxes. The availability of nest materials and vegetation coverage may affect the likelihood of finding hazel dormice at a location. The aim of the study is: (1) To investigate the preferences of hazel dormice for nesting materials today compared to four decades ago. (2) To investigate hazel dormice preferences for vegetation coverage at nest sites. In total, 148 hazel dormouse summer nests from the Bidstrup forests in Zealand (Denmark), were analysed. Of these, 82 were collected in the period A: 1980–1985 and 66 were collected in B: 2019–2020. In total 26 different nest materials were found. Beech was the major nest material in both periods, and Jacob’s selectivity index indicates that beech is selected for as nesting material and that hazel dormice may travel to collect beech leaves. Nests from period A contained more beech (W = 1521, p < 0.05) and less oak (W = 1304, p < 0.01) compared to nests from period B. Vegetation analysis showed that coverage of shrubs higher than 2 m above ground (W = 1.5, p = 0.07) may be of great importance for hazel dormice.