Bats Adapt When Food is Scarce: Hunting Prey with Different Calls

Bats are adaptable, and that's no more apparent than when food is scarce. Scientists have found that bat species will change their hunting strategies when they can't find their preferred prey. 

Echolocating bats have historically been classified into two groups: "loud" aerial hawkers who catch flying insects while on the wind and "whispering" bats that pick up prey from the ground. While some species can hunt in multiple ways, some are limited by the amplitude of their echolocation calls.

In this case, the researchers examined the desert long-eared bat, Otonycteris hemprichii, which is usually seen as a passive, "whispering" gleaner that picks up ground-dwelling invertebrates, such as scorpions. In order to examine these bats, the researchers used an acoustic tracking system. They recorded the bats flying at four different foraging and drinking sites and then compared the bats' flight height, flight speed, call duration, pulse interval and source levels with those of other gleaning bats.

The most interesting difference was the source levels of the bats. They were recorded calling at an average of 119 decibels. In gleaning bats, though, 75 decibels is more common. The scientists also noted that in the bats' faeces, there were prey species capable of flight, which suggests that the bats could switch between gleaning and hawking.

"Although whispering bats have been known to opportunistically catch insects on the wing, this doesn't appear to be the case here," said Talya Hackett, one of the researchers, in a news release. "All the bats' calls we recorded were loud and we didn't observe any low flying search tactics which suggests that the bats were exclusively aerial hawking."

The findings actually show that these bats are far more adaptable than previously realized. Not only that, but it seems to be able to switch its call behavior drastically.

"Changes in environmental conditions or prey availability could explain this change in the bats' behavior," said Marc Holderied, co-author of the new study. "We studied them towards the end of an exceptionally hot and dry summer so it's likely the usual prey animals were scarcer: desert scorpions, for example, become more inactive during dry conditions. As a result, the bats might have entered different habitats with artificial irrigation or attacked different prey, adopting a different foraging mode when their typical prey was scarce."

The findings are published in the Journal of Experimental Biology.