Behaviour 2019
Spatial resolution along the depth axis in bat biosonar
Leonie Baier1,2, Peter A. Wagenhäuser1, Lutz Wiegrebe1. 1Ludwig Maximilians University, Department Biology II, Martinsried, Germany; 2Technical University Munich, Chair of Zoology, Freising, Germany

Many echolocating bats forage close to vegetation - a chaotic arrangement where prey and foliage are positioned behind one another. Bats measure distance by the delay between outgoing call and returning echo. Delay-sensitive neurons form a topographic map in the auditory cortex, suggesting that bats can resolve echoes of multiple targets along the depth axis - a skill crucial for the forage-amongst-foliage scenario. We tested this hypothesis with an auditory virtual reality: We simulated a prey item embedded in two foliage elements. The simulated spacing between “prey” (target) and “foliage” (maskers) was defined by the inter-masker delay (IMD). We trained Phyllostomus discolor to detect the target and systematically varied both loudness and spacing of the maskers. We show that target detection is impaired when maskers are closely spaced (IMD <  1 ms), but improves with increased spacing: release from masking is about 5 dB for intermediate IMDs (1-3 ms) and increases to over 15 dB for large IMDs (≥ 9 ms). We conclude that prey would enjoy considerable acoustic protection from closely spaced foliage, but also that the range resolution of bats would let them “peek into gaps”.