// White-lipped Frog //
Just because frogs do not have protruding external ears like ours does not mean they cannot hear. Their ears are flat circular patches (aka tympanum) located behind each eye (see picture). These comprise of both inner ears and eardrums like ours but with one special adaptation – their eardrums are connected to the lungs!
Both the eardrums and lungs vibrate when the frog hears sounds. Sound transmitted from the lungs helps to equalise the pressure differences between the outer and inner surface of the tympanum, allowing them to croak loudly without damaging their own eardrums. This adaptation may also be useful in helping the frog to locate where other sounds are coming from.
You might also be wondering why frogs (like this one) are usually spotted sitting motionlessly and peering into the distance with their big dewy eyes. Why does it remain unfazed by the series of flashes fired by the photographer? Could it be too troubled by a recent rejection rejected by a mate?
Discounting my earlier anthropomorphic guess, I think the frog’s probably just waiting to catch the next unlucky insect that passes by…
June 2015, Tawau, Sabah.
Gunter Ehret & Elke Keilwerth (1994). The lung- eardrum pathway in three treefrog and four dendrobatid frog species: some properties of sound transmission. J. exp. Biol. 195, 329–343