Different foraging tactics in related animal taxa may be expected to cause species-specific differences in sensitivity to temporal and spatial variations of resources. To test this, we studied spatiotemporal dynamics of flight and foraging activity in seven insectivorous bat species in northern Poland using broadband ultrasound detection, recording of weather conditions, insect abundance, moon phase, and cover of floating vegetation. The seven species studied comprised six (genera Eptesicus Rafinesque, 1820, Pipistrellus Kaup, 1829, and Nyctalus Bowdich, 1825) that were classified as aerial hawkers and one ( Myotis daubentonii (Kuhl, 1817)) that was classified as a water-surface forager. Stepwise forward multiple regression models indicated that the prominent limiting factors for aerial hawkers were biomass of potential prey and air temperature. Analysis of the activity of the water-surface forager revealed no effect of food abundance or air temperature, but activity was negatively affected by floating vegetation (which masks echoes of prey items), fog (which absorbs echolocation calls), and moonlight (possible increased predation risk). Hence, trophic resources appear to have no significance as a limiting factor for species using microhabitats with unusually high prey abundance (e.g., water surface). Activities of such species, however, may be more affected by temporally changing detectibility of food items and vulnerability to predation pressure.

Temperate zone bats are small hetero therms with clearly patterned annual life cycles (Speakman and Thomas 2004). Their flight activity reveals significant seasonal variation (Rachwald 1992, Hayes 1997, Russ et al. 2003 and some descriptive studies have tried to interpret its re-current patterns as effects of annual life cycle. Different energy demands during pregnancy and lactation (Racey and Speakman 1987) result in different time spent outside the roost by female bats (Rydell 1993) and might be expected to result in different levels of bat activity recorded in foraging areas. Harsh winters force bats to migrate different distances or to hibernate (Fleming and Eby 2004, Speakman and [301] Acta Theriologica 55 (4): 301-314, 2010. R. 2010. Seasonal activity patterns of seven vespertilionid bat species in Polish lowlands. Acta Theriologica 55: 301-314.Data on seasonal dynamics of bat activity in central Europe are scarce, mostly restricted to either summer period or autumn swarming. Few studies provide extensive interspecific comparisons of temporal activity patterns. Through broadband ultrasound detection, temporal variation of flight activity was studied in seven insectivorous bat species in N Poland for the first time. Seasonal activity pattern of Myotis daubentonii (Kuhl, 1817) was clearly bimodal with the higher peak of activity in April and the second, smaller peak in August-September. The first peak is possibly associated with post-hibernal restoration of fat reserves, while the second one might result either from pre-hibernal fat accumulation, increase in energy demands of males during spermatogenesis or from dispersal of newly weaned juveniles. The highest flight activity of Nyctalus, Eptesicus and Pipistrellus bats was noted in summer months, reflecting mainly an increase in energy demands between pregnancy and lactation. However, a distinct, second peak in activity of N. noctula appeared at the end of September, probably matching the late migration wave of individuals from E Europe. The cluster analysis of species' activity patterns reflected division on different hunting tactics, but not migratory behaviour.

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