It is believed that they are extinct in the wild. They are lacking some of the inner ear structure but can hear within certain frequencies as they use thier lungs to pick up and transmit the sounds. See
http://www.jstor.org/pss/1446859 and
http://www.springerlink.com/content/gc4qupu2upac9e1r/ and
http://www.springerlink.com/content/u68j4f0q572816kv/ and
http://www.newscientist.com/article/mg1 ... sound.html
The arm waving and posture display is used because this species primarily calls in areas of heavy water flow in the stream which prevents the call from being audible so the signaling is used. The do call which can be heard when the animals are close together.
Ed
