Bioacoustics of Rhinopoma hardwickii

Activity patterns. Lesser Mouse-tailed Bats usually leave roosts 10-15 minutes after sunset, hunting in open spaces at heights of 10-15 m. They emerge from colony roosts in large groups. Prior to emergence, activity of colony increases with intensive audible vocalization and regrouping to spaces close to roost exit. Except for the southern Indian population, individuals are inactive in winter and often in large mixed colonies with the Greater Mouse-tailed Bat (up to 7000 individuals reported from Rajasthan ). Multiharmonic QCF calls with maximum energies at second harmonic of 30-40 kHz. During search flight in open spaces, repetition rates are c.10 Hz, and durations are 20-40 millisecond. When landing, repetition rate increases up to 40 Hz, and calls change to short (3-5 milliseconds) frequency-modulated (FM) notes with 5-10 kHz sweeps of particular harmonics. Audiogram shows peak sensitivity at 35 kHz. J. Habersetzer in 1981, studying echolocation behavior of Lesser Mouse-tailed Bats under natural conditions in Madurai, southern India , found significant increase of between-individual differences in frequencies of CF-calls when they flew in a group (frequencies were in three different bands: 30 kHz, 32-5 kHz, and 35 kHz), compared to common mean frequency 32-5 kHz when they flew alone. He proposed frequencyshift as a behavioral mechanism ofjamming avoidance.