Big brown bats (Eptesicus fuscus) emit intense search calls and fly in stereotyped flight paths as they forage in the wild

Abstract

The big brown bat, Eptesicus fuscus, uses echolocation for orientation and foraging, and scans its surroundings by aiming its sonar beam at obstacles and prey. All call parameters are highly adaptable and determine the bat's acoustic field of view and hence its perception of the echo scene. The intensity (source level) and directionality of the emitted calls directly contribute to the bat's acoustic field of view; however, the source level and directionality of the big brown bat's sonar signals have not been measured in the field. In addition, for bats, navigation and prey capture require that they process several streams of acoustic information. By using stereotypic flight paths in known areas, bats may be able to reduce the sensory processing load for orientation and therefore allocate echo processing resources to prey.Here we recorded the echolocation calls from foraging E. fuscus in the field with a microphone array and estimated call intensity and directionality, based on reconstructed flight trajectories. The source levels were intense with an average maximum source level of 138 dB (root mean square re. 20 µPa at 0.1 m). Furthermore, measurements taken from a subset of calls indicate that the echolocation signals in the field may be more directional than estimated in the laboratory (halfamplitude angle 30 deg at 35 kHz). We also observed that E. fuscus appear to follow stereotypic flight paths, and propose that this could be a strategy to optimize foraging efficiency by minimizing the sensory processing load.

Do you hear what I see? Vocalization relative to visual detection rates of Hawaiian hoary bats (Lasiurus cinereus semotus)

“…As expected, matches between acoustic and visual detections occurred proportionally more for near-range than for mid-range to far-range detections, likely indicating that nearby bats were more readily detected acoustically than those flying at greater distances (Skowronski & Fenton, 2009 Detection of ultrasound depends in part on the angle between a sound source and detector (Adams et al, 2012). Echolocation calls of bats can be highly directional (Hulgard, Moss, Jakobsen, & Surlykke, 2015), and aerial hawking bats can increase directionality to extend sonar range (Jakobsen, Brinkløv, & Surlykke, 2013). In addition, some species are capable of aiming echolocation "beams" off the direction of flight (Fujioka et al, 2014) and alternating the direction of those beams between successive pulses (Seibert, Koblitz, Denzinger, & Schnitzler, 2013).…”

“…Detection of ultrasound depends in part on the angle between a sound source and detector (Adams et al., ). Echolocation calls of bats can be highly directional (Hulgard, Moss, Jakobsen, & Surlykke, ), and aerial hawking bats can increase directionality to extend sonar range (Jakobsen, Brinkløv, & Surlykke, ). In addition, some species are capable of aiming echolocation “beams” off the direction of flight (Fujioka et al., ) and alternating the direction of those beams between successive pulses (Seibert, Koblitz, Denzinger, & Schnitzler, ).…”

“…Hawaiian hoary bats often predictably visit the same foraging areas on consecutive nights (Bonaccorso, Todd, Miles, & Gorresen, ), a behavior also noted in other studies of insectivorous bats (e.g., Entwistle, Racey, & Speakman, ; Meyer, Weinbeer, & Kalko, ; Wai‐Ping & Fenton, ). Bats foraging in a familiar natural environment are thought to use “foraging beats” and stereotypic flight paths, as well as rely on an internal map of their surroundings to reduce echo‐processing load and enable greater focus on tracking prey (Hulgard et al., ). Similarly, bats negotiating obstacles in a laboratory flight room also reduce call rates as they gain familiarity with their flight space (Barchi, Knowles, & Simmons, ; Holland & Waters, ).…”

“…and stereotypic flight paths, as well as rely on an internal map of their surroundings to reduce echo-processing load and enable greater focus on tracking prey (Hulgard et al, 2015). Similarly, bats negotiating obstacles in a laboratory flight room also reduce call rates as they gain familiarity with their flight space (Barchi, Knowles, & Simmons, 2013;Holland & Waters, 2007).…”

Acoustic localization of terrestrial wildlife: Current practices and future opportunities

“…Cable synchronization involves connecting ARUs or microphones to a central multichannel recorder or computer. This process is straightforward for microphone arrays deployed across small spatial extents (e.g., Wang et al, 2005), or multimicrophone ARUs used for DOA localization or hyperbolic localization of bats (e.g., Hulgard, Moss, Jakobsen, & Surlykke, 2016; Kojima et al, 2016). Running cables over large areas can be impractical or impossible (Mennill et al, 2012).…”