Meet the Common Shrub Frog

Did you know that Sri Lanka is a global amphibian hotspot? The credit for putting Sri Lanka on the global amphibian hotspot map goes to WHT (Wildlife Heritage Trust) founded by the Rolex Award laureate Rohan Pethiyagoda.

Rohan and his research associates including Kelum Manamendra-Arachchi, my mentor, conducted an extensive survey of the island’s amphibian fauna during the 1994-2003. The result of all these years of hard work was the discovery of a whopping 100-plus species of amphibians new to science! Most of them belong to the Oriental shrub frog genus: Philautus. This phenomenal discovery has pushed the total inventory of amphibians into the region of 140 species, which is simply mind-blowing considering that nearly all of them have been found in an area less than 800 sq.km of remaining rain forests in the "wet zone," and scattered over 100 forest fragments in what is the most populous biodiversity hotspot in the world—with a population density of 700 persons per sq.km!

While the above survey was to mainly discover new species, which they succeeded spectacularly, WHT's research work also necessarily involved the examination of type and other specimens preserved in museums worldwide—most notably in the British Museum of Natural History of collections made during 1850–1940. This extensive field research and museum work lead to the hard realisation that 21 amphibian species have gone extinct from Sri Lanka! The sad irony was some of them were only formally described as recently as 2007 as “new species,” —with their conservation status reading as “extinct.”

 How tragic is that?
Following the then available information, the Global Amphibian Assessment (GAA) in 2003 acknowledged that 19 species of Sri Lankan amphibians have gone extinct, which was 56% of the 34 confirmed cases of global amphibian extinctions recorded in the past five centuries—a record we cannot be too proud of.

The alarming extinction of amphibians in Sri Lanka appears to be largely a result of habitat loss with vast areas of island’s moist rain forests being decimated to make way for plantations of coffee, tea, rubber, and cinchona by the British colonials on their way to becoming a world superpower.

Despite the doom of habitat loss and resultant extinctions, Kelum and Rohan still maintain some feeble hope that some of the 21 labelled as extinct could indeed be still alive given that they described five extant species as "new" from a single specimen each, and as some of these are extremely cryptic, and hard to find.

It is rather paradoxical that Sri Lanka is the centre of a very high number of new species discoveries of amphibians while also accounting for the highest number of known amphibian extinctions at the same time. This is a result of extensive recent field explorations by the dynamic team at WHT combined with a re-examination of all historical material, which in turn has been possible only because so many species had been collected before their habitats disappeared altogether, and preserved in natural history museums worldwide in the colonial era of natural history explorations.

Of the spectacular batrachofauna in Sri Lanka, the Oriental shrub frog genus: Philautus shows an amazing radiation with a whopping 62 species described so far, out of which 19 are now labelled as extinct. Members of this genus have an unusual reproductive method, which is characterised by laying their eggs on the moist forest floor or on trees that develop directly into metamorphosed imagos or froglets, thereby bypassing the free-swimming tadpole stage. This is called direct development, or endotrophy, and according to this strange reproductive method, they undergo their ‘tadpole’ stage within the egg.

And with that long preamble, I am pleased to announce that among this celebrated coterie of amphibians, the Common Shrub Frog Philautus popularis is special in that it is the only Philautus found in my home garden! As the name implies, it is indeed a common one, calling virtually from every low shrub as the dusk descends. Formally assigned to the now extinct ‘catch-all’ species: Philautus variabilis, this little tree frog measuring 17.7-24.7mm from snout to vent in adult males is one of the 35 new species of amphibians described new to science in the Raffles Bulletin of Zoology by the indefatigable team at the WHT in 2005(Madhava Meegaskumbura was also part of the team.)

Of the 43 extant species, it is important to note that 15 are known only from a single site each, and 11 from 2 -usually nearby sites each. The team at WHT has found that most of the newly discovered species are restricted to an area less than 5 sq.km in extent. Interestingly, they have also found that many species of Philautus have extremely small ranges regardless of the availability of continuous habitat. This is believed to be one of the primary reasons for their amazing diversity in Sri Lanka. It could also explain why there are such high cases of extinctions as habitat loss can easily kick a species into the pit of death.

The boys of this endemic Common Shrub Frog are often found calling their lungs throats out to the girls at the neighbourhood, and I was able to take some photos recording this, after a few failed initial attempts.

I now know how to approach them.