Bats Change Foraging Strategy When Food Is Scarce

Echolocating bats have historically been classified into two groups: 'loud' aerial hawkers who catch flying insects on the wing and 'whispering' gleaners that pick up prey from the ground. While some bat species can forage in multiple ways, others have limited flexibility in the amplitude of their echolocation calls. Dr. Talya Hackett from the University of Bristol (UK) and colleagues studied the desert long-eared bat (Otonycteris hemprichii) (image), said to be a passive 'whispering' gleaner that picks up ground-dwelling invertebrates, such as scorpions, from the desert floor. Using an acoustic tracking system, the researchers recorded the bats flying at four different foraging and drinking sites in the Arava and Judean Deserts in Israel. They then compared the bats' flight height, flight speed, call duration, pulse interval, and source levels with those of other gleaning bats. The results were reported in the September 1, 2014 issue of the Journal of Experimental Biology. Differences were found in all these variables, with the most striking being the source levels: bats were recorded calling at an average of 119 decibels, akin to a 747 jet on take-off, when around 75, akin to a car engine, is more usual when gleaning (though these sounds occur at a high frequency, beyond the range of human hearing). Analysis of the bats' feces also indicated 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 (aerial hawking). Dr. Hackett said: "Although whispering bats have been known to opportunistically catch insects on the wing, this doesn't appear to be the case here.
Login Or Register To Read Full Story