How bats optimize foraging

By the time a Japanese pipistrelle bat (shown here) has finished foraging for the night, it has eaten up to 20% of its body mass in bugs and flies. Such prodigious feeding is necessary because foraging itself is energy intensive. Some bats spend two-thirds of their daily energy budget on the activity. Efficient foraging is therefore paramount. Emyo Fujioka of Doshisha University in Kyoto, Japan, and his collaborators have set themselves a goal of determining how the Japanese pipistrelle maximizes its food intake. Their principal tool is an array of 32 microphones positioned around a stream where local bats habitually forage. By analyzing the ultrasonic chirps emitted by the bats, the researchers can track not only the bats’ flight paths but also the directions in which the bats aimed the chirps to echolocate their prey. What’s more, because the chirps become more frequent the closer a bat gets to its prey, the researchers can determine when its targeting has been successful. One efficient feeding strategy that bats could conceivably adopt is to locate two targets that could be captured in quick succession. Fujioka and his collaborators developed a numerical model that embodied the strategy and compared it with their data. They found that when a bat identified two nearby targets, it adjusted its flight path to consume them one after the other, typically within 1 second. The tactic worked most often when the bat made an aerial turn of 0.6π–0.8π to line up the prey. (E. Fujioka et al., Proc. Natl. Acad. Sci. USA 113, 4848, 2016, doi:10.1073/pnas.1515091113 .)