This is a short note about a couple of frogs from South East Asia that are rarely seen or photographed.

The narrow-mouthed frogs, Microhylidae, include over 300 species in 69 genera, distributed throughout the warmer parts of the world but notably in Madagascar, New Guinea and South East Asia, where diversity within the family is at its greatest.  Knowledge of the natural history of many species is poor or non-existent.  The incidence of direct development, or of a short, non-feeding tadpole stage, seems to be widespread throughout the Family, however.

Borneo Treehole Frog, Metaphrynella sundana, Sukau, Borneo

Typical microhylids are small and plump with pear-shaped bodies.  Most are terrestrial or burrowing species but a few are arboreal. Arboreal microhylids often breed in water that has collected in leaf-axils, or in holes in trees.  Tree hole breeders occur in Madagascar, among the Cophylinae subfamily, specifically in the genera Anodonthyla, Platypelis, Cophyla and in some Plethdontohyla species (Vences and Glaw, 2007).

In Asia, tree-hole breeding is restricted to a single genus, as far as we know.  This is Metaphrynella, with just two species: M. pollicaris, from the Malaysian Peninsula, and M. sundana, from Borneo.  Their ranges, therefore, do not overlap and, furthermore, M. pollicaris is an upland species found only above 550m (Berry, 1975) whereas M. sundana  is a lowland species, occurring only below 700m (Inger and Steubing, 1997).  Both are small, chubby species and not obviously adapted to climbing, although the tips of their digits are expanded slightly and they also have fleshy pads at the base of all their toes that probably aid in climbing as well.  Males set up calling stations in small water-filled tree-holes and call each night with a single, repetitive peeping call, in an attempt to lure a female.  She has to climb the tree and enter the hole in order to spawn.

In the lowlands forest of Borneo, M. sundana is ubiquitous and common and its calls can be heard almost every night.  We found males in tree holes and, on one occasion, two males occupied the same hole.  We also found females on the forest floor and climbing into small shrubs, presumably foraging for food.  Inger  and Stuebing assert that the tone of the call varies and suggest that this is due to the varying sizes, and therefore the acoustic qualities, of the hole from which they are calling.  To our untrained ears, all calls sounded similar.  The tadpole of this species is apparently unknown, which is strange given its abundance.

Malaysian Treehole Frog, Metaphrynella pollicaris, Bukit Fraser, Malaysia

Our experience of the Malaysian Peninsula species, M. pollicaris, is more limited and the species appears not to be abundant.  We found a single presumed female on the road during a rain storm at Fraser’s Hill (illustrated) and a male was calling at Bukit Larut.  The latter proved to be difficult to locate as it was calling from inside a hollow metal post marking the edge of the road; this had corroded in places allowing water, and the frog, to enter.  We repeatedly walked back and forth past the post several times before we realised where the call originated.

Rain forest alongside the Danum River, Borneo, habitat of the Borneo Treehole frog

References

Berry, P. Y. 1975.  The Amphibian Fauna of Peninsular Malaysia.  Tropical Press, Kuala Lumpur.

Inger, R. F. and Stuebing, R. B., 1997.  A Field Guide to the Frogs of Borneo.  Natural History Publications, Kota Kinabalu.

Vences, M. and Glaw, F. 2007.  A Field Guide to the Amphibians and Reptiles of Madagascar (third edition).