Social trills of the pipistrelle bat (Pipistrellus pipistrellus) are quieter than their echolocation calls, but have a greater range.

Under natural conditions, the sound pressure level of social trills and echolocation calls of pipistrelle bats was measured as peak equivalent sound pressure level (peSPL) with the aim of estimating the range of the signals. Thirty-eight echolocation calls and 55 social trills, whose distance from the microphone was known, were evaluated. The social trills were approximately 8 dB quieter than the echolocation calls but had a significantly greater range because of their lower call frequency. Based on the American National Standards Institute/Acoustical Society of America [ANSI/ASA (2024) S1.26-2014, Methods for Calculation of the Absorption of Sound by the Atmosphere (Acoustical Society of America, New York)] standard, we examined the propagation of the signals under different conditions of humidity, temperature, and air pressure. The results show that in calm weather the potential ranges can vary by a factor of two to three. Assuming a detection threshold of 20 dB, we determined ranges for an echolocation call of between approximately 30 and 80 m under realistic conditions and for a social trill of between 60 and more than 120 m.