When a single bat targets a tasty treat, it closes in quickly for the kill. But what happens when a competitor tries to muscle in on the act? What strategies do competing bats use to catch their prey in aerial dogfights? Knowing how individuals pursue stationary and moving prey, Chen Chiu and her colleagues from the University of Maryland wondered how duelling bats track each other and their prey as they compete to catch a snack (p. 3348).
Chen Chiu first became interested in this problem when she was training bats to catch tethered mealworms. ‘Sometimes I used to let two or three bats fly together and compete for the worm. I found they chased each other and one dominant bat got the worm,’ remembers Chiu. Intrigued by the behaviour, Chiu and her colleagues, Wei Xian and Cynthia Moss, decided to record the bats' manoeuvres and echolocation calls to find out how competing bats hunt.
Releasing pairs of bats into a 7 m×6 m×2.5 m flight enclosure, the trio filmed the duelling animals in infrared light while recording the bats' echolocation cries with 16 microphones as they competed for a suspended mealworm. Remembering that individual bats catch the tethered mealworms within a matter of seconds, Chiu says, ‘In the two bat situation, they were circling around the room for a while and did some chasing. It usually took about one minute for one of the bats to get the prey.’ Chiu also noticed that over the course of the dogfight, the trailing bat usually outmanoeuvred the leader in the closing moments to catch the reward.
Next, Chiu analysed the direction of each bat's echolocation calls to find out where the trailing bat was ‘looking’ as it pursued the leader. ‘This was pretty difficult,’ laughs Chiu. Having successfully allocated each echolocation call to one of the two bats, Chiu teamed up with P. S. Krishnaprasad and Puduru Reddy to compare the direction that the trailing bat was flying with the direction of the invisible line that joins the two bats' positions at all times to find out how it tracked its rival. If the trailing bat was simply following the leader, the direction that it was flying would always point towards the leader, but if the trailing bat was using the strategy that individual bats use when hunting free-flying prey, then the trailing bat would fly so that the invisible line (joining it to the leading bat) maintained a constant orientation as the bats progressed.
Surprisingly, the pursuing bat was simply following the leading bat instead of using the strategy that individual hunters use when tracking prey. The team also noticed that when the bats flew head on towards each other they averted their cries, presumably to avoid jamming each other's echolocation signals.
So why is the trailing bat more successful at catching prey than the leading bat? Chiu suspects that the trailing bat is at an advantage because it might be able to disguise its presence by going quiet during the pursuit, as well as chasing the leading bat off in the final crucial moments before trapping the prey. The team also suspects that when large groups of bats leave their roosts ‘en masse’, they may use the same pursuit strategy, following the bat in front to successfully avoid collisions with their neighbours.