ECHOLOCATION ACTIVITY OF DAUBENTON’S BAT (MYOTIS DAUBENTONII) AND COMMON
PIPISTRELLE (PIPISTRELLUS PIPISTRELLUS) IN RELATION TO INSECT ABUNDANCE,
HABITAT AND ELEVATION IN AN UPLAND RIVER CATCHMENT
Abstract
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.