Frequency shifts of echolocation pulses in a cluttered environment: Comparison between Pipistrellus abramus and Miniopterus fuliginosus.

Abstract

Changes in frequency range (ΔF) of FM echolocation pulses were recorded with an onboard wireless microphone (Telemike) for Pipistrellus abramus and Miniopterus fuliginosus in a cluttered environment created by dense chain‐row obstacles. The duration of echo streams (ESD) from the chains reached ∼40 ms when the bats were flying toward the chain‐row obstacles. P. abramus emitted pulses in pairs (strobe group) with 20–40 ms interpulse intervals (IPIs), which occasionally created pulse‐echo ambiguity (IPI was shorter than ESD). When successive echo streams did not overlap, ΔF within strobe groups was less than 2–3 kHz. When overlap occurred, Δ F increased to 5–6 kHz (F‐test, P < 0.001). By shifting frequency range of successive FM pulses, P. abramus appeared to assign echoes to the corresponding pulses and avoid pulse‐echo ambiguity. Similar finding was previously reported in Eptesicus fuscus. On the other hand, M. fuliginosus never emitted pulses in a strobe group, and IPIs were always adjusted to be longer than ESDs. Thus, the amount of ΔF was less than 2 kHz, which corresponded to that in P. abramus without pulse‐echo ambiguity. These comparative results suggest that echolocation strategy in the cluttered environment is different between two FM bat species. [Work supported by JSPS and ONR.]