Measurement of Abundance and Activity of the Northern bat Eptesicus nilssonii, in Forests and Edge habitats in Sweden - Tools for Conservation Planning

Abstract: Good estimations of habitat preference and activity of bats in different habitats are of great importance when planning for conservation or assessing consequences of exploitation. The objective of this study was to compare two different methods for abundance estimation: line- transects (active taxation) and point taxation by autobox recordings (passive taxation), and correlation analyses were made between data from these methods. The species used was Eptesicus nilssonii, which is easy to identify and one of the most common bat species in Sweden. Differences in abundance between edge zones and non-edge zones were tested. The equations from the correlations would allow the use of passive taxation data for abundance estimates. Using the equations produced in the correlation analysis, and data collected in other projects at different sites in southern and central Sweden, an estimation of the total number of E. nilssonii in southern and central Sweden was made. This data was also used in order to test differences in abundance between habitats close to and further away from water. However, no differences in abundance between different habitats could be seen. Significant correlations were found between active and passive taxation data. The total number of E. nilssonii individuals in southern and central Sweden was estimated in two different ways: 1. by using the total number of passive taxation observations, to about 5 million individuals and, 2. by using the number of five minute period containing at least one observation, to 4 million individuals. How to increase the precision of these figures are discussed.