The calls of the poorly known Philippine Flat-headed frog, Barbourula busuangensis (Anura: Bombinatoridae)

We describe the call of Barbourula busuangensis, a peculiar and elusive fully aquatic frog endemic to the Palawan archipelago of western Philippines. This species is so poorly known that most of its basic natural history characteristics (re-productive mode and seasonality, diet, age structure, lifespan) remam to be discovered. Contrary to the calls of other frog species adapted to life in fast-flowing streams, the call of B. busuangensis has a very low fundamental frequency around 250 Hz, with an average duration of 1.2 seconds. Additionally, its pulsed, amplitude modulated structure differs from the tonal calls of all known species in its most closely-related (sister) clade, the genus Bombina.