Their call is a strange metallic, insect-like two syllable call. It could be described as "di-dink", although the two syllables are hard to distinguish
Here is a single call from one individual -
But when we look at the spectrogram for that call, we see it is actually two separate notes. The carrier (dominant) frequency of the call is somewhere between 4.2 and 4.3 kHz. The problem is that the two notes are given so rapidly, that they can't really be distinguished by the human ear/brain. The space between the notes here is approximately 1/100th of a second!
But if we slow down the speed of the recording by 50%, we can discriminate both notes of this call as distinct. This is exactly the same recording shown above slowed down 50% (with the pitch kept constant) -
Here is a recording of a small group of individuals -
and here is a larger chorus. This file had to be edited to remove the calls of several other species, resulting a slightly "tinny" recording.
© Chris Harrison 2014