Echolocation by Insect-Eating Bats

[ "Hans-Ulrich Schnitzler () is professor and head of the Lehrstuhl Tierphysiologie of the University of Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany."]; [ "Elisabeth Kalko is professor and head of the Abteilung Experimentelle Ökologie of the University of Ulm, Albert Einstein Allee 11, D89069 Ulm. E. Kalko is a staff member and H.-U. Schnitzler is a research associate of the Smithsonian Tropical Research Institute, Panama. E. Kalko is also a research associate at the National Museum of Natural History in Washington, DC."]
BioScience (Impact Factor: 5.44). 09/2009; DOI: 10.1641/0006-3568(2001)051[0557:EBIEB]2.0.CO;2
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    ABSTRACT: Smooth spherical beads were used as S+. Differently textured beads were used as S-, each presented one at a time as an alternate to S+. Can bats integrate echoes over time to discriminate sonar targets? We used the same behavioral paradigm with newly designed stimuli. Smooth spherical Delrin balls were machined with a groove cut 1 mm in depth around their circumferences. Holes were drilled to hang them from the ceiling. Each bead was machined identically, but presented horizontally (S+) or vertically (S-). A random sampling of individual echoes with no regard to sequence or position makes the targets indistinguishable. Can the bats still discriminate the groove orientation when the beads are at different heights? S+ and S-were hung at different heights, randomized from trial to trial, to determine whether the bat could continue to discriminate the orientations. METHODS Experimental Paradigm We trained bats to discriminate between two tethered beads under low IR illumination, one designated the positive stimulus (S+) and the other the distracter (S-). The bats were trained to seek out and hit S+ suspended from the ceiling and avoid hitting S-, also suspended from the ceiling. The positions of the targets in the room changed with every trial, and the target positions were randomized. S+ and S-were suspended for the full duration of each trial. Training Using operant conditioning, the bats were trained in the following order, with some modifications per bat: 1. Train bat to catch mealworms from tether 2. Associate bridge stimulus with food reward while bat on platform 3. Allow bat to learn to land on platform 4. Train bat to connect physical contact with S+ (either on platform or hanging in the room) to the bridge stimulus and food reward on platform 5. Introduce S-to teach bat to prefer S+ and avoid S-Experiments were run in a large carpeted flight room (6.4 x 7.3 x 2.5m) lined with acoustic foam in low light, long wavelength conditions. Sonar vocalizations were recorded using ultrasonic microphones and analyzed off-line. The bat's 3-D flight path was reconstructed using stereo images taken from high-speed video recordings. An array of 16 microphones was used to record the directional aim of the sonar beam of the bat as it flew. Echo Recordings The stimuli were ensonified by playing computer generated FM sweeps and recording the returning echoes.
    International Congress of Neuroethology, Vancouver; 01/2007
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    ABSTRACT: Behavioural flexibility: the little brown bat, Myotis lucifugus, and the northern long-eared bat, M. septentrionalis, both glean and hawk prey We present behavioural data demonstrating that the little brown bat, Myotis lucifugus, and the northern long-eared bat, M. septentrionalis, can glean prey from surfaces and take prey on the wing. Our data were collected in a large outdoor flight room mimicking a cluttered environment. We compared and analysed flight behaviours and echolocation calls used by each species of bat when aerial hawking and gleaning. Our results challenge the traditional labelling of M. lucifugus as an obligate aerial-hawking species and show that M. septentrionalis, which is often cited as a gleaning species, can capture airborne prey. As has been shown in previous studies, prey-generated acoustic cues were necessary and sufficient for the detection and localization of perched prey. We argue that the broadband, high-frequency, downward-sweeping, frequency-modulated calls used by some bats when gleaning prey from complex surfaces resolve targets from background. First, because calls of lower frequency and narrower bandwidth are sufficient for assessing a surface before landing, and second, because there are few, if any, simple surfaces in nature from which substrate-gleaning behaviours in wild bats would be expected.  2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. The foraging strategies used to obtain prey, like preferred prey type, are used to classify predatory animals. For example, the northern pike, Esox lucius, is an ambush predator capable of bursts of speed when attacking prey that pass close by its hidden position. Behavioural observations of individuals capturing prey corroborate physiological observations of neuromuscular, biome-chanical and cardiovascular systems indicating that ambush is how pike catch their prey (Ahlborn et al. 1997). Furthermore, through foraging strategy specializ-ation, sensory systems have evolved in a complementary fashion: it is no coincidence that raptors have remarkable visual acuity (Reymond 1985). The little brown bat, Myotis lucifugus, has traditionally been labelled an aerial-hawking species (e.g. Barclay 1991), and the northern long-eared bat, Myotis septentrionalis, a gleaning species (e.g. Foster & Kurta 1999). However, anecdotal evidence suggests that M. lucifugus can take prey from surfaces (Simmons & Stein 1980) and that M. septentrionalis captures airborne prey (Miller & Treat 1993). These 5–8-g Nearctic insectivorous species are sympatric over much of their range, share a similar diet, and are often found together at night roosts and hibernacula (Barclay & Fenton 1980; Caceres & Barclay 2000). Both species are commonly observed flying within cluttered habitats (van Zyll de Jong 1985). On inspection of live individuals, these species can be difficult to distinguish (van Zyll de Jong 1985), although the ears and tragi of M. septentrionalis are longer than those of M. lucifugus (Caceres & Barclay 2000). Norberg & Rayner's (1987) ecological morphology model categorizes them together as species that will fly slowly and be highly manoeuvrable and thus well suited to foraging in cluttered environments. The echolocation calls used by M. septentrionalis while gleaning prey are reported to be of shorter duration (which prevents pulse-echo overlap at short distances), higher peak frequency (which should provide higher resolution of small objects as a result of shorter wave-length) and broader bandwidth (greater frequency range, greater resolution) than the echolocation calls used by M. lucifugus (Faure et al. 1993). However, in Faure et al.'s study, the calls used by M. septentrionalis during gleaning were compared to the search calls of M. lucifugus. The echolocation call sequences produced by M. lucifugus dur-ing aerial attacks on airborne, insect prey are among the first recorded for any bat species and are used to describe
    Animal Behaviour 11/2003; 66:847-856. · 3.07 Impact Factor
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    ABSTRACT: Patterns of interspecific and intraspecific variation in the three endemic species of Malagasy Triaenops bats were investigated using morphology and bioacoustics. Adult bats were captured at different localities across the island, measured, and their echolocation calls recorded. On average, male T. auritus and T. furculus have shorter forearms (47.0 and 44.0 mm, respectively) and emit higher frequency calls (107.8 and 113.1 kHz, respectively) than females (47.5 and 45.7 mm and 95.6 and 98.2 kHz, respectively), representing a form of reversed sexual dimorphism (females larger than males). However, T. menamena shows typical patterns of sexual size dimorphism with males having a longer forearm (51.7 mm) and lower frequency echolocation calls (82.3 kHz) than females (49.0 mm and 93.5 kHz, respectively). When segregated by sex, there was a strong allometric relationship between forearm length, used as a measure of body size, and the resting frequency in these three species, as well as two African hipposiderids (T. afer and Cloeotis percivali). Triaenops auritus males and both sexes of T. furculus deviated from the relationship between these two variables. Hypotheses are explored to explain the drivers of these sexual dimorphism patterns. On the basis of the allometric relationship, the strong correlation is in parallel to other groups of bats and is probably associated with ecological constraints. Recent phylogenetic analyses showed a separation of Afro-Malagasy Triaenops into two sister clades: T. auritus/T. furculus (suggested to be placed in a new genus, Paratriaenops) and T. menamena/T. afer. The patterns of sexual dimorphism in these taxa are congruent with clade membership. Further studies are needed to understand strategies used by these taxa when in sympatry to share habitat and ecological niches.
    Acta Chiropterologica 12/2013; 15(2):431–439. · 0.89 Impact Factor

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