Spatiotemporal variation in activity of bat species differing in hunting tactics: effects of weather, moonlight, food abundance, and structural clutter

Abstract

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.

Variability of foraging and roosting activities in adult females of Daubenton’s bat (Myotis daubentonii) in different seasons

“…Although this was proven in many species of aerial hawking bats (e.g., Racey & Swift 1985;Rydell 1989;Catto et al 1995;O'Donnell 2000;Ciechanowski et al 2007), Daubenton's bats seem to be quite tolerant to relatively very low temperatures (Dietz & Kalko 2007) and they were observed foraging at as low temperatures as -3 • C (Ciechanowski et al 2007). Accordingly with observations above, we did not observe any significant effect of minimum nightly temperature on the activity of radio-tracked Daubenton's bats.…”

Chronobiology by moonlight

“…the bats appear to be responding to the effect of light on their prey behaviour [76]. Another water surface forager whose activity is negatively correlated with moonlight is Daubenton's bat (Myotis daubentonii) [77]. A study of activity levels of the white-throated round-eared bat (Lophostoma silvicolum), a gleaning insectivorous bat which relies mainly on passive acoustic cues to find prey, and its main prey item katydids, found that both were significantly more active during the dark periods associated with new Moon [78], suggesting that the reduced activity can be attributed to reduced prey availability [78].…”

Habitat preferences of bats in anthropogenically altered, mosaic landscapes of northern Poland

“…This problem, however, affects this study only to a minor extent. Intensive summer mist netting conducted in the Gdańsk Pomerania region revealed that more than 90 % of Myotis bats captured belong to Daubenton's bat Myotis daubentonii (Ciechanowski 2002;Ciechanowski et al 2002;Ciechanowski et al 2007) and this allowed the assumption that most Myotis echolocation calls recorded there during the summer season are emitted by the same species. If possible, the presence of M. daubentonii was confirmed by either visual observation (i.e.…”