There are three species of green-blooded, turquoise-boned frogs known from Vietnam. A few years ago we discovered that one of these species had an advertisement call so spectacular in its complexity and variation that it became known as “the frog that sings like a bird”. Further fieldwork has now revealed that all three of these frog species sing like birds, having similarly “hyperexpended vocal repertoires”.
The forests of central and northern Vietnam and parts of Laos and southern China are home to a group of three, relatively small (male SVL < 25 mm) frogs with pointed snouts, green blood and turquoise bones. All three poorly-known species, Gracixalus quangi, G. gracilipes and G. supercornutus, look similar and are most closely related to each other. They all lay their eggs on the tips of leaves where they develop into tadpoles and then drop into the shallow water below.
In 2010 my colleagues and I discovered Gracixalus quangi (Quang’s Tree Frog) in the remote mountains of north-central Vietnam. At the time, we recorded its amazing calland reported that it had a non-stereotypical, hyperextended vocal repertoire. Put more simply, in contrast to most frog species that repeat more or less the same advertisement call over and over again, the calls of G. quangi were variable in structure, duration, amplitude and frequency. No two calls were the same. But what about the calls of the other green-blooded frogs? Their calls, like much of their biology, were completely unknown.
The next year, I came across a high-elevation swamp deep in the forests of central Vietnam echoing with a familiar, bird-like call. This time it belonged to the spikiest of the green-blooded frogs, Gracixalus supercornutus. The following year in the mountains of northern Vietnam I heard another bird-like call, this time it belonged to G. gracilipes. We recorded and analysed the calls of both these species and we can now say for sure that all three species of green-blooded frog from Vietnam have hyperextended vocal repertoires- they all “call like birds”.
So why do these little frogs have such complex and variable calls? We suspect that some parts of the calls serve to defend territories and others to lure the females. But the reason that these little frogs have far more to say than your average frog is still a mystery. Future research on these tiny green species will hopefully reveal the answers, and give us insight into the biology of these poorly-known and vulnerable species.
Dr Jodi Rowley
Curator, Amphibian & Reptile Conservation Biology, Australian Museum & UNSW Sydney.