First harmonic shape analysis of Brazilian free-tailed bat calls during emergence

Abstract

Echolocating bats can adapt calls when facing challenging echolocation tasks. Previous studies have shown that bats can change their pulse duration, pulse repetition rate, or vary their start/end/peak frequencies depending on behavior. Even though this kind of signal investigation reveals important findings, these approaches to analysis use bulk parameters that may hide subtleties in the call structure that could be important to the bat. In some cases, calls may have the same start and end frequencies but have different FM shapes and meet different sensory needs. In the present study, we demonstrate an algorithm for extracting the first harmonics of the Brazilian free-tailed bat (Tadarida brasiliensis) to investigate how the shape of the call changes. High pass filtering, power banded time-frequency analysis, and search algorithms were used to isolate the first harmonics. By tracking the first harmonics, the detailed frequency modulation shapes of different bat group sizes were obtained, and the difference among those traces was measured. The detailed shape analysis will provide a new insight into the adaptive call design of bats.