Bats Aggregate to Improve Prey Search but Might Be Impaired when Their Density Becomes Too High

Abstract

Social foraging is a very common yet extremely complex behavior. Numerous studies attempted to model it with little supporting evidence. Studying it in the wild is difficult because it requires monitoring the animal's movement, its foraging success, and its interactions with conspecifics. We present a novel system that enables full night ultrasonic recording of freely foraging bats, in addition to GPS tracking. As they rely on echolocation, audio recordings of bats allow tapping into their sensory acquisition of the world. Rapid changes in echolocation allowed us to reveal the bats' dynamic reactions in response to prey or conspecifics—two key behaviors that are extremely difficult to assess in most animals. We found that bats actively aggregate and forage as a group. However, we also found that when the group became too dense, bats were forced to devote sensory attention to conspecifics that frequently entered their biosonar "field of view," impairing the bats' prey detection performance. Why then did bats fly in such high densities? By emitting echolocation calls, bats constantly provide public information about their detection of prey. Bats could therefore benefit from intentionally flying at a distance that enables eavesdropping on conspecifics. Group foraging, therefore, probably allowed bats to effectively operate as an array of sensors, increasing their searching efficiency. We suggest that two opposing forces are at play in determining the efficient foraging density: on the one hand, higher densities improve prey detection, but on the other hand, they increase conspecific interference.

The origins and diversity of bat songs

“…Territorial behaviors at the roost have been observed for many species, and not coincidentally most examples of singing have been collected at the roost. However, as new tools emerge for recording and tracking the nightly activity patterns of individuals (Cvikel et al 2014) evidence is accumulating that bats do compete for food and defend preferred foraging territories, even if only temporarily or seasonally (Corcoran and Conner 2014). To look more closely at this, we next compare representative examples of the interplay between singing and territorial behaviors from four different bat families.…”

Natural search algorithms as a bridge between organisms, evolution, and ecology

“…Combining technologies for measuring the structure and dynamics of sensory cues, such as geographical information system (GIS)-based and computational modeling of water currents or winds (28,38), acoustic methods for quantifying the locations of prey aggregations (39), and onboard sensors that measure realtime conditions at the animal's location (40), will dramatically increase what we can learn about search strategies using animal tracking data from the field.…”

Bats enhance their call identities to solve the cocktail party problem

“…Bats use the echoes of self-generated acoustic signals to hunt, navigate, and orient themselves in total darkness. Bats also hunt or navigate with a number of conspecifics 11–13 . Because echolocating bats actively emit signals to scan their environments, groups of bats flying together experience acoustical interference caused by echoes from irrelevant directions and signals belonging to conspecifics 14, 15 .…”