This study in Lithuania showed that the abundance dynamics of the common dormouse (Muscardinus avellanarius) populations were comparatively “smooth”, without outbreaks and crashes. Decreases and increases of abundance continued for some years, and abundance differed no more than three-fold in two successive years. A close negative correlation was revealed between spring population density and percentage of juveniles in the autumnal population. The last parameter is a consequence of reproduction success, which determined the scale of population increase in autumn and was due to several factors. Among them, proportion of breeding adult females had the greatest significance and was inversely proportional to population density in spring. Some young-of-the-year females usually joined the breeding process, when population density was low. The proportion of late breeding cases, when juveniles were born in September, was also negatively correlated with spring population density. The number of litters produced by one female during the season, and the average litter size also influenced reproduction success. The negative correlation between population density and reproduction success shows the presence of a reproduction success based pattern of density dependent self-regulation in M. avellanarius in the populations investigated.
Geographically peripheral populations are likely to experience suboptimal conditions, and several population characteristics may be influenced. The aim of the present study was to assess characteristics of the populations of hazel, forest and fat dormice on the northern periphery of their ranges in continental Europe in comparison to populations situated in the rest of their ranges. The dormouse populations analysed were found to be distinct from other populations in many aspects of their ecology. On this northern periphery of the ranges, the dormouse activity season is shorter and ends earlier. The population density is also lower, but inter-annual abundance dynamics are comparatively stable. Except the shorter breeding season however, there is no clear general pattern regarding other aspects of reproduction. The composition of the vegetable food used by dormice is rather specific. Contrary to expectations, the proportion of food of animal origin is not increased in the dormouse diets. The main habitat requirements of dormice are similar to those in other parts of their ranges, though the composition of woody plant species in the dormouse habitats is different. Dormice living on the northern periphery of their ranges show a high degree of adaptability to local conditions, but factors limiting their distribution are not clear yet.
In Lithuania, common dormice Muscardinus avellanarius destroyed 6.6% of 3807 bird nests with eggs in nestboxes at two study sites. M. avellanarius occupied nests of pied flycatcher Ficedula hypoleuca without eggs or nests with incomplete clutches most often, ate unhatched eggs, but did not kill or bite nestlings and adult birds. M. avellanarius were very seldom found in nestboxes with nests of tits Parus spp. Edible dormice Glis glis destroyed 14.3% of 498 bird nests with eggs or nestlings at two study sites, mostly nests of F. hypoleuca and great tit Parus major. G. glis ate birds’ eggs, killed and ate nestlings and adult birds. Forest dormice Dryomys nitedula made the biggest impact on birds nesting in nestboxes. They destroyed 20.5% of 171 nests with eggs or nestlings, ate eggs, killed and ate nestlings and adult birds. The most common impact of D. nitedula on birds in nestboxes was the killing of adults, either breeding or just looking for nest sites, and F. hypoleuca made a majority among birds killed. F. hypoleuca was most affected by all three dormice species in Lithuania, while P. major was impacted less and only by G. glis and D. nitedula.
Since the publication of “The Atlas of European Mammals” in 1999 plenty of new data have been collected on the distribution of Apodemus spp. in Lithuania. These data have changed our knowledge of the comparative distribution of ?A. sylvaticus and A. uralensis in the country. Essentially, A. uralensis is widespread in the north-western part of the country, whereas A. sylvaticus is found only in southern and eastern Lithuania. Both species reach the limits of their geographical ranges in Lithuania.
On the basis of previous studies of the common dormouse Muscardinus avellanarius concentrated on deciduous woodlands in the southern counties of Great Britain, it was stated that optimal habitat for M. avellanarius should contain a high diversity of suitable shrub and tree species to provide continuous food supply through activity season and appropriate physical structure. However, both the present review of M. avellanarius habitats within its distributional range and recent dormouse studies in other parts of Great Britain indicate that M. avellanarius actually inhabits a much wider variety of habitats, and do not require specialised habitats as previously supposed. M. avellanarius habitats in Lithuania differ considerably from the optimal habitats described for this species, about 40 % of localities being situated in coniferous- dominated forests. Habitat quality may result in a very low average population density of only about one adult per hectare. However, despite of absence of optimal habitats and low population density, M. avellanarius is widespread in Lithuania, and no decline is observed in their abundance and distribution. Forest management (increasing forest cover, planting of native tree species, not too large fragmentation of forest tracts) has been favourable for M. avellanarius in Lithuania.
The diet of the forest dormouse, Dryomys nitedula, was studied in Lithuania, which is situated on the north-western edge of its range. The diet composition of D. nitedula changes constantly over the activity period. From late April until mid-July, food of animal origin dominates the diet, while vegetable food prevails from mid-July until early September. Over the entire activity season, food of animal origin comprises on average 63 % of dormouse diet by volume estimates. Four main food groups – birds, adult insects, insect larvae and millipedes – dominate, but their proportions vary over the course of the season, as does the composition of vegetable food
used by D. nitedula. Among vegetable food, dormice feed on blossoms of
Norway spruce, oak and aspen in May, cones of Norway spruce during June-August, raspberries, birch seeds and fruits of glossy buckthorn in July and August and oak acorns in late August and early September. The composition of vegetable food used by D. nitedula in Lithuania is rather specific in comparison to other parts of the range and shows high
dormouse adaptability to local conditions. In different years, the proportions
of vegetable and animal food, as well as their compositions, vary in the dormouse diet. Dormice can accumulate sufficient fat reserves for hibernation feeding on both vegetable and animal food.
Throughout most of the distributional range, the fat dormouse, Glis glis, relies heavily upon European beech as a key species in its habitat. In Lithuania however, situated beyond the continuous range of the beech, pedunculate oak becomes the essential tree in habitats of G. glis. In Lithuania, the dormouse activity season lasts from mid-May to mid-October, young are born during the short period from late July to mid-August, and the mean litter size is 5.9 young. Population density is low (0.8-2.0 ind./ha after hibernation and 1.2-4.8 ind./ha in autumn), but relatively stable. The mean body weights of adults (98 g after hibernation and 128 g before hibernation) are among the lowest across the range. Lithuanian dormice differ from those living in beech-dominated habitats by their lower population density and lower body weight. Such differences may be due to acorns being less suitable food for G. glis in comparison to beech nuts. In terms of inter-annual abundance dynamics, the G. glis population is comparatively stable as years in which dormice fail to reproduce are infrequent in Lithuania.