Feeding in an unpredictable environment: yearly variations in the diet of the hazel dormouse Muscardinus avellanarius

Yearly variations in the diet composition of the hazel dormouse Muscardinus avellanarius were studied in typical dormouse habitat in Lithuania over 5 years (2010–2014) with different feeding conditions. A high proportion of birch seeds in the dormouse diet in two out of 5 years was a very much unexpected result. Dormice consumed them from mid-June until late October even when the most preferable food—hazel nuts—was abundant. In autumn when accumulating fat reserves for hibernation, hazel dormice fed on four main food sources—fruits of glossy buckthorn, oak acorns, hazel nuts and birch seeds. The consumption of these food sources was directly related to their availability. During the study period, only one, two or three of these food sources were abundant in any particular year, while others were absent or scarce. In total, the fruits of glossy buckthorn and oak acorns accounted for the major portion of dormouse diet in autumn. Dormice living in habitat with irregular fruiting of the main food plants are adapted to feed on varying food sources and can switch from one food source to another in different years.