Acoustically eavesdropping bat predators take longer to capture katydid prey signalling in aggregation

Abstract

Prey signalling in aggregation become more conspicuous with increasing numbers and tend to attract more predators. Such grouping may, however, benefit prey by lowering the risk of being captured due to the predator's difficulty in targeting individuals. Previous studies have investigated anti-predatory benefits of prey aggregation using visual predators, but it is unclear whether such benefits are gained in an auditory context. We investigated whether katydids of the genus Mecopoda gain protection from their acoustically eavesdropping bat predator, Megaderma spasma, when calling in aggregation. In a choice experiment, bats approached calls of prey aggregations more often than those of prey calling alone, indicating that prey calling in aggregation are at higher risk. In prey capture tasks, however, the average time taken, and the number of flight passes made by bats before capturing a katydid, were significantly higher for prey calling in aggregation as compared to calling alone, indicating that prey face lower predation risk when calling in aggregation. Another common anti-predatory strategy, calling from within vegetation, increased the time taken by bats to capture katydids calling alone but did not increase the time taken to capture prey calling from aggregations. The increased time taken to capture a prey calling in aggregation compared to solitary calling prey offers an escape opportunity, thus providing prey signalling acoustically in aggregations with anti-predatory benefits. For bats, greater detectability of calling prey aggregations is offset by lower foraging efficiency, and this trade-off may shape predator foraging strategies in natural environments.

Satellite remote sensing of environmental variables can predict acoustic activity of an orthopteran assemblage

“…Maintaining a continuous sing-along but extending their signaling for several hours also comes with its downsides, which require further adaptations in response to visual predators, as we will discuss later. Previous works have described how katydid aggregation in space can lower the effectiveness of bat captures ( Prakash et al, 2021 ). Although we did not test the relationship between acoustic frequency and duration of the diel calling activity, our preliminary analysis suggests that species with lower dominant frequencies tend to call for shorter periods ( e.g ., Cricket1 vs Katydid5; Fig.…”

Multimodal duetting in katydids under bat predation risk: a winning strategy for both sexes

“…Similar to other substrate-gleaning bats, M. spasma may opportunistically use different prey cues in different scenarios [38][39][40], with flight providing a powerful cue, possibly detected by echolocation, since they do not approach flight sounds [23]. Unlike Micronycteris microtis, M. spasma rarely approach silent, motionless, walking or tremulating prey even in the absence of vegetation cover [40,41]. It is likely that future studies might reveal similar hierarchies of risk across predatory bat and katydid prey species, with flight being the most risky behaviour, given that acoustic call cessation and synchrony are successful anti-predator strategies against eavesdropping bats [41,42].…”

“…Unlike Micronycteris microtis, M. spasma rarely approach silent, motionless, walking or tremulating prey even in the absence of vegetation cover [40,41]. It is likely that future studies might reveal similar hierarchies of risk across predatory bat and katydid prey species, with flight being the most risky behaviour, given that acoustic call cessation and synchrony are successful anti-predator strategies against eavesdropping bats [41,42]. Thus, selection against flight in prey species is likely to be widespread and perhaps stronger than selection against signalling.…”

Acoustic signalling in Orthoptera

“…One hypothesis is that singers that synchronize are less vulnerable to phonotactic predators and parasitoid flies, which find it more difficult to locate a single singer within the chorus. Some support for this idea has been found in Mecopoda (Prakash et al, 2021), where acoustically orienting bats take longer to capture an individual singing in a chorus than one singing alone.…”