How bats catch their prey
|
Guided missile strategy used
|
THE PURSUIT strategy of bats is different from that reported in earlier studies of target pursuit in humans and other animals.
The big brown bat solves a rather complex geometrical problem to minimise the time it takes to intercept flying insects. This has been discovered by a University of Maryland research team using infrared video cameras and an array of microphones in its bat lab.
The strategy that echolocating bats use to track and catch erratically moving insects is much like the system used by some guided missiles to intercept evasive targets, according to a University of Maryland press release.
Adaptive behaviours
A paper on the study appears in the May issue of PLoS Biology.
"Says psychology professor Cynthia Moss, a co-author of the study:
"These adaptive behaviours include agile flight and head-aim control, as well as adjustments in the timing patterns of sonar vocalisations, all finely coordinated to allow the bat to capture a free-flying insect in complete darkness and in the snap of a finger."
A technique used by humans and other animals such as fish and dogs and one way to intercept a target moving at fixed speed in a straight line is constant bearing.
"Constant bearing is a simple, intuitive way of doing complicated mathematical calculations," says lead author Kaushik Ghose. "It's the quickest way to get to a predictably moving target." Enter the bat, which uses sound rather than sight, to track its prey.
Ultrasonic pulses
The bat emits a series of ultrasonic pulses through its mouth to search its environment. When the pulses hit upon an insect that could be dinner, they bounce back to the bat to alert it to the insect's presence. But insects fly about erratically and may be in the open for only seconds at a time.
The team took infrared video and sound recordings of eight big brown bats intercepting both free flying and tethered insects in Moss's specially designed bat lab to see just what methods a bat uses to make the lightning fast interception.
Flight manoeuvres
By slowing the video, the team reconstructed the bats' flight and tracking manoeuvres to reveal that bats do not use the constant bearing method.
The bat locks its head on its target, much like a baseball player who keeps his eyes on the ball, and maintains the lock-on throughout the interception manoeuvre, even as its flight direction changes.
The bat constantly changed its bearing angle and speed in response to the insect's rapid movements.
"The bat keeps the compass direction to the target a constant, but it changes its flight direction at the same time," says Ghose.
"So, when the bat chases an insect, if the insect is initially located to the northwest, the bat manoeuvres to always keep the target to the northwest while closing distance.
"This strategy is called parallel navigation after the parallel nature of the bearing lines. Interestingly, in the late 1940s engineers working on the problem of how to program guided missiles to hit their targets implemented a similar strategy.
"The next easier thing is to maintain a fixed angle between yourself and the target. But the bat has done one better.
It's worked out ahead of time where it thinks the insect will end up and leads its flight to do that. It turns out the bat's strategy is time-optimal for catching erratically moving targets." — Our Bureau
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
