Robust Doppler Shift Compensation in Freely Flying Bats Under Acoustic Interference.

Noise is ubiquitous to all biological and ecological systems and is of pivotal importance to acoustically signaling species. To counter the detrimental effects of noise, animals have adopted a range of strategies. Different strategies generally help to mitigate, but rarely restore the performance to noise-free scenarios. Here, we document that the performance of Doppler shift compensation (DSC), a highly precise echolocation behavior, is immune to various types of acoustic interference at moderately high noise levels in flying Pratt's roundleaf bats (Hipposideros pratti). The DSC performance of individual bats was quantified under 10 types of bandpass-filtered noise and echolocation calls from seven bat species, apart from a silence control condition. We found that H. pratti maintained high DSC performance across all playback conditions. Surprisingly, we found evidence that H. pratti exhibited higher DSC precision in experimental conditions of narrowband noise and echolocation calls of one heterospecific bat species. The main energy of these acoustic stimuli coincided with the minimum (terminal) frequency of the frequency-modulated component of the dominant second harmonic in the echolocation calls of H. pratti. Thus, contrary to the widespread view, acoustic interference does not universally impair motor performance, and instead, some species may exhibit improved performance under certain noise conditions.