IVth International Conference on Dormice (Rodentia, Gliridae)

WEIGHT CHANGES OF THE COMMON DORMOUSE (MUSCARDINUS AVELLANARIUS L.) DURING THE YEAR IN LITHUANIA

Juskaitis, R.

Institute of Ecology, Akademijos 2, LT-2600 Vilnius, Lithuania, e-mail: juskaitis@takas.lt

More than 5000 individuals of M. avellanarius were weighed during investigations carried out in Lithuania in 1981-1999. The aims of this paper are: 1) to present weight dynamics of separate M. avellanarius demographic groups during the active season; 2) to investigate weight as a possible determinant of age in M. avellanarius; 3) to compare the weight of M. avellanarius in Lithuania with weights from populations in other parts of its distribution.

The majority of males awoke from hibernation with non-exhausted fat reserves: their average weight was 20.4 g in the first half of April. The weight decreased gradually till June, and was stable from June to July (between 17.0 g to 17.9 g). The increase in weight began in August and reached a maximum before hibernation in early October (29.8 g). The maximum registered weight in males before hibernation was 42.8 g. Females usually awoke from hibernation later than males, early in May, with an average weight of 16.0 g. Two slight peaks observed in the weight dynamics curve of females - in early June and early August - were connected with pregnancy. Weight gain began in September and reached 27.0 g in early October. The heaviest female caught in Lithuania weighed 35.0 g.

The weight of juveniles depended on the time of birth, although the weight dynamics curves in separate juvenile age groups were similar. Their average weight increased gradually by around 5 g each month. Only in September - October was the increase faster: about 10 g per month. Before hibernation the average weight of juveniles born in May-June (26.4 g) was similar to adult weights. Some of these juveniles weighed more than 30 g in early October, and the maximum registered weight was 33.5 g. The average weight of juveniles born in August was only 15.0 g in early October. Only solitary individuals weighed more than 20 g, maximum weight was 24.8 g. The weights of juveniles born in July lay between these values.

Use of weight to determine the age of M. avellanarius is very limited because the weights of separate age groups (mean ± 2SD) overlap in many cases. It is possible to identify juveniles from early litters according to their weight from late July to mid-August. Later on in the year age class weight distributions overlap and cannot be differentiated before hibernation. The weights of juveniles born in August do not overlap with the weights of adults in September. In September-October, the difference between the mean weight of juveniles born in May-June and juveniles born in August is about 10 g, although the mean ± 2SD still displays slight overlap. In the cases where weights (mean ± 2SD) overlap additional indicators are necessary to determine age. Fur coloration, which changes with the age, can be used to identify independent juveniles and adults.

Comparisons of M. avellanarius weights from Lithuania with limited data from other parts of its distribution (Likhachev, 1967; Schulze, 1973; Catzeflis, 1983; Bangura, 1988) suggests that dormouse weights may be higher in populations in north of its range than in populations in the south, especially in autumn before hibernation.

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