title: 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 (half-amplitude 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.
authors.affiliation: Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark khulgard@biology.sdu.dk.
authors.forename: Katrine
authors.initials: K
authors.lastname: Hulgard
authors.affiliation: Department of Psychological & Brain Sciences, The Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218-2686, USA.
authors.forename: Cynthia F
authors.initials: CF
authors.lastname: Moss
authors.affiliation: Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark.
authors.forename: Lasse
authors.initials: L
authors.lastname: Jakobsen
authors.affiliation: Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark.
authors.forename: Annemarie
authors.initials: A
authors.lastname: Surlykke
mesh_terms: D000818:Animals; D002685:Chiroptera / Q000502:physiology*; D004455:Echolocation; D005247:Feeding Behavior / Q000502:physiology*; D005426:Flight, Animal; D008396:Maryland; D009949:Orientation; D011235:Predatory Behavior
keywords: Attention; Bat echolocation; Directionality; Flight path; Sensory load; Source level