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

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 aggregates more often than those of prey
calling alone, indicating that prey calling in aggregation were 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 aggregates as compared to calling
alone-, indicating that prey face lower predation risk when calling in
aggregation. We also tested the effectiveness of another common
anti-predatory strategy: calling from within vegetation clutter.
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 as compared to solitary calling prey offers an escape
opportunity for the prey, thus providing prey signalling acoustically in
aggregation with anti-predatory benefits.