Abstract
The flight activity pattern of an aerial-hawking vespertilionid Pipistrellus nathusii has been investigated over different water bodies in northern Poland. Broadband ultrasound detection revealed that the species hunted over wooded sites mainly at dusk and dawn, following a clear bimodal pattern of activity. On the contrary, open sites were used by P. nathusii mainly in the midnocturnal period, thus their activity at post-midnight was significantly higher than at dusk. We discuss the observed differences on a background of existing knowledge on activity rhythms of flying insect abundance that are always reported as bimodal (with dusk and down peaks), irrespective of site and habitat type. Anti-predatory behaviour appeared to be the most likely reason to explain contrasting patterns of bat activity in both groups of sites. However, we also discuss other hypotheses with regard to data about insect abundance, wind speed, and temperature obtained from the same sites.
©2009 by Walter de Gruyter Berlin New York
