Perch-hunting in insectivorous Rhinolophus bats is related to the high energy costs of manoeuvring in flight |
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Authors: | Christian C Voigt B-Markus Schuller Stefan Greif Björn M Siemers |
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Institution: | 1. Evolutionary Ecology Research Group, Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315, Berlin, Germany 2. Sensory Ecology Group, Max Planck Institute for Ornithology, Eberhard-Gwinner-Stra?e, 82319, Seewiesen, Germany
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Abstract: | Foraging behaviour of bats is supposedly largely influenced by the high costs of flapping flight. Yet our understanding of
flight energetics focuses mostly on continuous horizontal forward flight at intermediate speeds. Many bats, however, perform
manoeuvring flights at suboptimal speeds when foraging. For example, members of the genus Rhinolophus hunt insects during short sallying flights from a perch. Such flights include many descents and ascents below minimum power
speed and are therefore considered energetically more expensive than flying at intermediate speed. To test this idea, we quantified
the energy costs of short manoeuvring flights (<2 min) using the Na-bicarbonate technique in two Rhinolophus species that differ in body mass but have similar wing shapes. First, we hypothesized that, similar to birds, energy costs
of short flights should be higher than predicted by an equation derived for bats at intermediate speeds. Second, we predicted
that R. mehelyi encounters higher flight costs than R. euryale, because of its higher wing loading. Although wing loading of R. mehelyi was only 20% larger than that of R. euryale, its flight costs (2.61 ± 0.75 W; mean ± 1 SD) exceeded that of R. euryale (1.71 ± 0.37 W) by 50%. Measured flight costs were higher than predicted for R. mehelyi, but not for R. euryale. We conclude that R. mehelyi face elevated energy costs during short manoeuvring flights due to high wing loading and thus may optimize foraging efficiency
by energy-conserving perch-hunting. |
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