Victoria Todd

and 2 more

Riparian habitats have high insect abundance and consequently provide good foraging opportunities for insectivorous bats. Here we investigate how insect abundance, temperature, season, and elevation affect the foraging behaviour of Daubenton’s (Myotis daubentonii) and common pipistrelle (Pipistrellus pipistrellus) bats along the river Wharfe in north Yorkshire. Insect abundance correlated positively with ambient air temperature. Abundance reached a maximum around sunset before dropping to low levels with frequent zero captures throughout the middle of the night. There was often a second smaller peak in insect abundance around sunrise. Insects at all elevation habitats were mainly dipterans, and most (92%) of these were nematocerans. There was a mismatch between peak insect abundance and bat detections, with highest insect detection just before bats arrived in the evening or after they left in the morning. Insect abundance and bat Feeding Buzz Ratios (FBR) did not differ significantly between treeless and tree-lined habitats. Significantly more M. daubentonii detections were recorded in August than in May, but there was no significant difference in the number of mean feeding buzzes between months. More P. pipistrellus FBRs were recorded at lower elevations; however, there was no elevational difference in FBR for M. daubentonii, although more FBRs were recorded for this species. Detections of M. daubentonii were fairly constant throughout the night, while P. pipistrellus exhibited large variations in number of passes per hour. P. pipistrellus arrived c.a. half an hour earlier at tree-lined habitats than tree-less habitats, likely taking advantage of protective tree cover to gain additional foraging time when insects are more abundant. M. daubentonii, on the other hand, generally arrived later. There was no correlation between FBR and number of aerial insects for either species. Bat detections (and therefore presence) is influenced by factors other than the availability of aerial prey.