A spectral jamming avoidance response does not help bats deal with jamming

Abstract

6For decades, researchers have speculated how echolocating bats deal with acoustic 7 interference created by conspecifics when flying in aggregations. It is thus surprising that 8 there has been no attempt to quantify what are the chances of being jammed, or how such 9 jamming would affect a bat's hunting. To test this, we developed a computer model, 10 simulating numerous bats foraging in proximity. We used a comprehensive sensorimotor 11 model of a hunting bat, taking into consideration the physics of sound propagation and bats' 12 hearing physiology. We analyzed the instantaneous acoustic signals received by each bat, and 13 were able to tease apart the effects of acoustic interference and of direct resource 14 competition. Specifically, we examined the effectiveness of the spectral Jamming Avoidance 15 Response -a shift in signal frequencies -which has been suggested as a solution for the 16 jamming problem. As expected, we found that hunting performance deteriorates when bats 17 forage near conspecific. However, applying a Jamming Avoidance Response did not improve 18 hunting, and our simulations clearly demonstrate the reason: bats have adequate natural 19 signal variability due to their constant adjustment of echolocation signals to the task. The 20 probability to be jammed is thus small and further shifting the frequencies does not mitigate 21 spectral jamming. Our simulations reveal both negative and positive insight: they show how 22 bats can hunt successfully in a group despite potential sensory interference and they suggest 23 that a Jamming Avoidance Response is not useful. 24 A: One Bat Scenario B: Five Bats Scenario Figure 1: Examples of individual and group hunting of the simulated bats (also see 85 supplementary movie). (A)A single simulated bat flying in the arena with 5 prey items. The 86 bat detects two prey items and decides to pursue the closest one (moth a). Panel 1 shows the 87 trajectories of the bat (black) and the moths (blue), the positions of each emitted signal (green 88 dots), and the location of the capture (black cross). Panel 2 shows the bat's velocity (gray), 89 the distance (black) and relative angle (blue) to target. Panel 3 shows the bat's received 90 acoustic scene for the section marked by a gray dashed line, including the envelopes of the 91 following signals: the transmitted signals (black), the received prey echoes (green), and the 92 received masking signals (red). Panel 4 shows a spectrogram of the same segment as in panel 93 3. Note how the signals' frequency drops at the final terminal buzz. (B) Three bats (out of five 94 in the arena) hunting in an environment with 10 moths. Bat 1 detects and pursues a moth, 95 while conspecifics (bats 2 and 3) fly nearby, emitting echolocation signals some of which mask 96 (or jam) the echoes received by bat 1. Instances of jamming are marked with red diamonds in 97 (3) (2)

Bats dynamically change echolocation parameters in response to acoustic playback

“…Since frequency adjustments occur frequently and under various conditions, an adaptation that purely depends on a JAR may not be sufficient to orient collision-free in the presence of signal interferers. This hypothesis gains support by recent simulations that have tested for the effectiveness frequency adjustments when navigating in noisy environments (Mazar and Yovel, 2019). Note that some studies reported that bats do not shift their frequency in response to acoustic interference (Götze et al, 2016) or that the frequency shifts are correlated with the object's distance rather with the presence of an acoustic interferer (Cvikel et al, 2015).…”