Versatility of biosonar in the big brown bat,Eptesicus fuscus

Abstract

Infrared cameras and ultrasonic microphones were used to record big brown bats (Eptesicus fuscus) flying in natural conditions at night while they hunted for insects. As expected, bats avoided obstacles while flying through vegetation and intercepted flying prey in the open. But bats also appeared to capture insects near and possibly on the ground and near or in vegetation, flew low over water to drink, and pursued each other in aerial "dogfights." In less than a minute, the same bat often used echolocation for several different tasks, showing a wider repertoire of sonar-guided behavior than revealed by previous observations limited to seeing bats flying against the evening sky or being photographed in fixed fields-of-view.

FM echolocating bats shift frequencies to avoid broadcast–echo ambiguity in clutter

“…1A Inset) (3,4). These bats change the interpulse intervals (IPIs), the initial high frequencies and terminating low frequencies of FM sweeps, the duration, and the amplitude of broadcasts according to surrounding conditions such as the distance to nearby objects (3)(4)(5)(6)(7). Each sonar broadcast impinges on objects at different distances to form a stream of echoes returning at different delays.…”

“…Clutter interference is exacerbated by broadcast-echo ambiguity, creating a worst-case situation-self-generated clutter resulting from the use of too-short IPIs. The obvious effectiveness of echolocation in clutter (5,6,12,13) makes it desirable to learn how bats achieve this performance. When flying in dense clutter, big brown bats emit nearly all their sonar sounds in pairs, called "strobe groups," with shorter IPIs between members of the pairs set off by longer IPIs between one strobe group and the next (3,8,12,13).…”

Big brown bats and June beetles: Multiple pursuit strategies in a seasonal acoustic predator–prey system

“…8) from a previous report show not only the bat entering the vegetation but also several beetles leaving. 18 These flights into vegetation were different from aerial pursuits in that the bat's echolocation sounds often were not detected when the bat was in proximity to the vegetation (audio tracks of Mm. 7 and 8), whereas bats intercepting beetles in the open produced the full complement of search, approach, and terminal signals characteristic of pursuit (audio tracks of Mm.…”

“…4,17 Most recently, thermal-imaging video cameras make it possible to watch and record bats without the illumination constraints of other video methods. 18 This paper illustrates different capture behaviors from recordings made with infrared cameras that ''see'' bats and large flying insects from their own body heat. Observations are directly documented as video/audio files rather than as verbal descriptions augmented by multiple-exposure strobe photographs and measurements of selected parameters of the maneuvers, as has been the practice in most prior research.…”

Detection of targets colocalized in clutter by big brown bats (Eptesicus fuscus)

“…Video recordings made with thermal-imaging cameras document that these bats are able to successfully catch insects in flight ͑Simmons, 2005͒. However, the same infrared video recordings reveal that big brown bats can also capture beetles from vegetation and sometimes even land on the ground to seize prey ͑Simmons, 2005; Simmons et al, 2001͒. Some kinds of insects taken as prey by big brown bats, such as crickets or katydids, are not commonly observed to fly at night and presumably must be taken from substrates such as the ground or vegetation ͑Fullard et al, 2005;Kurta and Baker, 1990͒. Beetles swarming in vegetation make buzzing sounds that are audible to bats ͑Hamr and Bailey, 1985͒, and crickets and katydids communicate with each other acoustically, in both cases providing bats with potential cues for passive hearing to detect and localize prey.…”