Bats have evolved a sophisticated way to avoid interference jamming their echo signals, research has shown.

Scientists in the US believe lessons learned from the discovery could lead to more efficient sonar and radar systems.

When bats fly in packs there is a danger that the high-pitched sounds they use to locate objects and prey might overlap and interfere with one another.

A similar problem arises when a bat chases a moth through thick foliage. Signals bouncing off the leaves can overlap and set up interference.

In both cases, the result could be confusion and the creation of "phantom" objects which are not there. But bats get around the problem by tweaking the frequencies of the sounds they emit to hunt and navigate, researchers found.

The creatures also take a mental snapshot of each broadcast and the echo it produces to differentiate one signal from another.

To investigate how they cope with crowded environments, scientists mounted tiny microphones on the heads of big brown bats (Eptesicus fuscus).

They recorded sounds the bats emitted while navigating through an obstacle course of plastic ceiling-to-floor chains.

Other microphones placed in the room recorded the echoes produced from the bats' broadcasts. At the same time, the bats were filmed with high-resolution video cameras.

The recordings showed the bats were faced with a potentially confusing cascade of overlapping echoes.

They appeared to get around the problem by logging a "mental fingerprint" of each broadcast and corresponding echo in their memories. That allowed them to separate signals by very slightly altering their frequencies so that one did not match the other.

The bats were found to change the frequency of their broadcasts by no more than six kilohertz.

Study leader James Simmons, from Brown University in Providence, Rhode Island, said: "They've evolved this so they can fly in clutter. Otherwise, they'd bump into trees and branches."

The research appeared in the journal Proceedings of the National Academy of Sciences.