How big is best? Various nest box sizes and their acceptance by Muscardinus avellanarius (Rodentia: Gliridae)

The hazel dormouse (Muscardinus avellanarius) can be found in nest boxes intended for birds and dormice throughout its distributional range. To minimize competition with other potential nest box inhabitants such as the edible dormouse (Glis glis) and hole-nesting passerines like the blue tit (Cyanistes caeruleus), we successfully tested nest boxes with a 21 mm entrance hole in previous studies. The only competing species still able to pass through the entrance hole were the wood mouse (Apodemus sylvaticus) and possibly the yellow-necked mouse (Apodemus flavicollis). To further optimize the nest boxes we tested whether their internal space might be important for selection by the hazel dormouse. Starting in 2015, we set up groups of four wooden nest boxes varying in base area (50×50 mm, 60×60 mm, 70×70 mm and 80×80 mm, respectively) with 21 mm entrance holes. The nest boxes were placed in an identical array at 15 stations spaced at intervals of 30 m along a hedgerow. By doing regular nest box checks and documenting all species found we investigated which nest box types were used most often by the hazel dormouse in order to detect possible preferences. So far, the data show a more intensive use of the nest boxes that provided the largest internal space, i.e. 80×80 mm.