Washington, Sep 5 (IANS): When food is scarce, bats change their tactics and turn more flexible in their echolocation behaviour.

They could switch foraging mode from "gleaning" to "hawking" and alter the volume of their calls accordingly, researchers at the University of Bristol found.

Although whispering bats have been known to opportunistically catch insects on the wing, this does not appear to be the case.

"All the bats' calls we recorded were loud and we did not observe any low-flying search tactics which suggests that the bats were exclusively aerial hawking," explained Talya Hackett, a professor from the University of Bristol.

The study looked into the foraging techniques of the desert long-eared bat Otonycteris hemprichii in Israel, a passive 'whispering' gleaner that collects ground-dwelling invertebrates from the desert floor.

Using an acoustic tracking system, the team recorded the bats flying at four different foraging and drinking sites and compared the bats' flight height, flight speed, call duration, pulse interval and source levels with those of other gleaning bats.

From an analysis of the bats' faces, they found that their diet included prey species capable of flight, such as flies, moths and beetles.

This suggests that the bats switched from passive gleaning to capturing airborne insects or aerial hawking.

"Changes in environmental conditions or prey availability could explain this change in the bats' behaviour," concluded co-author Marc Holderied.

The study appeared in the Journal of Experimental Biology.