There is handedness everywhere you look. Fish tend to turn to the right when evading a predator, parrots often prefer to grasp with one foot over the other and we all know the human experience from first hand. But handedness doesn't end there. Many animals show a dominance of one ear over the other when it comes to interpreting the sounds made by members of their own species: primates, mice, sea lions and horses all seem to use their right ears in preference to the left to listen to other animals of the same species. And Guangzhan Fang and Yezhong Tang from the Chengdu Institute of Biology, the Chinese Academy of Sciences, explain that electroencephalogram data suggest that music frogs (Babina daunchina) preferentially listen to the calls of other music frogs with their right ears. However, they needed behavioural evidence to confirm that the frogs really do listen out for each other with their right ears (p. 740).
Having headed off on the 6 h drive to the Emei Mountains, Fei Xue collected 48 of the vocal animals from ponds in the area, ready to test their auditory responses back in the lab. Xue then played sounds – ranging from males calling from burrows (which are known to be sexually attractive to females) and males calling out in the open (which are less alluring to females) to claps of thunder and the shrieks of music frogs under snake attack – to individual frogs while filming the amphibians’ reactions.
Analysing the frogs’ movements – they are unable to turn their heads to locate a sound, so they turn their bodies instead – Xue, Fang, Tang, Ping Yang, Ermi Zhao and Steven Brauth found that the frogs tended to present their right ears to the sexually attractive calls of males in burrows, while they turned to the left and moved further away from the speaker playing alarming shrieks and claps of thunder. ‘These results support the idea that in anurans [frogs] right ear preference is associated with perception of positive or neutral signals… while a left ear preference is associated with perception of negative signals, such as predatory attack’, say Fang, Tang and their colleagues.