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Two populations of the pipistrelle bat Pipistrellus pipistrellus in southernmost Sweden were studied for eight consecutive breeding seasons using bat boxes. The population living in the vicinity of an industrial area had a declining population trend when compared to that form a rural area. Mass indices in September, when fat accumulation prior to hibernation has started, were also lower compared to those obtained in the rural area. The levels of organochlorine residues and of cadmium were also higher in the population living close to the industrial area. The proximate cause of the decline, however, is assumed to be deteriorating feeding conditions due to drainage and water pollution.

A pipistrelle bat (Pipistrellus pipistrellus) population in southernmost Sweden was studied for eight consecutive breeding seasons by means of bat boxes. Survival rates were calculated using Cormack's stochastic technique. The mean survival rate of adult females exceeded that of territorial males. Annual variations in survival rates were most evident in males, low rates being observed in years following wet autumns. Energy constraints imposed on territorial males by the mating system, a resource defence polygyny, were assumed to account for the differences obtained in survival rates between the sexes.

The relationships of faunal diversity and vegetation structure were studied in twenty deciduous forest plots in South Sweden, all of them managed. Following animal groups were censused: shrews (Soricidae), bats (Chiroptera), voles (Cricetidae), fieldmice (Muridae), birds (Aves), groundliving beetles (Coleoptera), spiders (Araneida), and harvestmen (Opilionidae). The analysis of the 22 vegetation variables was made by means of repeated and rotated PCA. Rarefaction was used to ordinate the bird species richness of the different forest plots. The multivariate vegetational analysis resulted in three distinct and readily interpretable components: horizontal and vertical spatial heterogeneity, and mean basal area. The number of small mammal species (except bats) was greatest in forests with great amount of understory while the number of bat species increased with increasing mean basal area. The number of bird species in a fixed number of territories was also highly correlated with the mean basal area. Hence, maximum bird species richness was obtained in mature forests but not in those with greatest vertical heterogeneity. The invertebrate communities showed very few distinct relationships to the vegetation structure. Dominance decreased as vegetation complexity increased. Dominance also decreased with increasing species richness in all faunal communities studied.

The social organization of the pipistrelle bat (Pipistrellus pipistrellus) was studied by means of bat boxes in southern Sweden. The males set up territories around a roosting site in the beginning of the summer at the same time as the females formed nursing colonies. After breeding, the females joined the single males in their day roosts establishing transient mating harems. Subsequently, immatures arrived at the mating grounds. The immature females, which probably attained sexual maturity during their first autumn, were admitted to the day roosts of the harem males, in contrast to the immature males. The size of the harem was dependent on the total number of females present on the mating grounds. The size, however, was also restricted by some factor, presumably the quantity of food resources in the surroundings of the specific roost site, or the capability of the harem male for mating. The mating system in the pipistrelle bat is best characterized as a resource defence polygyny. Available data on other related temperate species indicate a similar social organization in Pipistrellus nathusii and Nyctalus noctula.

The food habits of the mink in Sweden were studied in three different habitats by means of scat analyses. The entire material contained 4,738 scats. There were very marked seasonal variations due to changes in the relative availability of the prey. The principal food groups were mammals, mainly rodents, birds, fish, and crayfish. Crayfish occurred most frequently in the summer food, due to its higher activity in the warm months which increased its vulnerability. Fish was consumed preferentially in winter and spring. The great availability in these seasons was a result of increased vulnerability due to low water temperature. Frogs were secondary food and occurred most frequently in the diet at seasons when the mink changed its food habits. Birds occurred most frequently in the diet during migration and breeding seasons. Rodents constituted a very variable source of food due to the great fluctuations of their number. Their availability influenced the food habits in a conspicuous manner, particularly in the northern area investigated. The greatest changes in the food habits occurred in late spring and in the autumn. Differences between habitats with regard to food habits were most marked in summer. At other seasons the food habits were dominated by the great fish consumption. Pe3ioMe

Activities of six minks (Mustela vison) in southern Sweden were monitored during nine different periods in 1968-69 by radio-tracking techniques. Diel activity patterns were determined and related to availability of prey, reproduction cycle, and certain environmental factors. 1. All the wild male minks studied were mainly nocturnal at all seasons. The level of activity tended to increase with increasing length of night and with decreasing temperature. In general, the activity peaks of male mink corresponded to peaks in prey activity. 2. The female studied showed a very low activity during pregnancy. During the litter period when she was mainly diurnal her level of activity was considerably higher.