Echolocation in the noctule (Nyctalus noctula) and horseshoe bat (Rhinolophus ferrumequinum)

Summary

• 1. When catching flying prey under laboratory conditionsRhinolophus ferrumequinum typically emit FM-CF-FM signals (Fig. 2). Except for the last two sounds during approach and final buzz the FM-parts are fainter than the CF-component by a factor of 0.76+-14 (Fig. 1). The final FM-part was undetectable in some signals emitted during approach (Fig. 3).

• 2. In obstacle avoidance flights both, preceding and final FM-parts are prominent and louder than the CF-part by a factor of 1.14 to 1.63 (Fig. 1 and 3). Bandwidths of the FM-components increased from ca. 3.5 to 12 kHz for the starting and from 12 to 20 kHz on the average for the final FM-sweep (Table 1).

• 3. In the open field during cruising flightsNyctalus noctula emits pure tones of 22.5 to 25.0 kHz without any frequency modulated components and a duration of 10 to 50 ms (Fig. 4). Brief frequency modulated signals sweeping from ca. 50 to 20 kHz in about 1–2 ms are emitted during pursuit of prey (Fig. 4).

• 4. Under laboratory conditionsNyctalus noctula does not emit pure tones and is not able to catch flying prey in a flight chamber 10.5×3.5×2.15 m in size. During flights towards a landing platformNyctalus noctula invariably emits brief frequency modulated pulses. During an individual flight the structure is not changed (Fig. 5).

• 5. InNyctalus noctula specific features of the echolocation pulses, e.g. frequency range swept through, presence of harmonics and double pulses (Fig. 6) are maintained during an individual flight. These specific characteristics of the signal may be used to identify echoes belonging to its own emitted echolocation pulse.