It was 2014, and the monsoon was in full swing in Coorg. The rain had paused momentarily and we’d quickly hiked up to a spot near Honey Valley Estate, where my former colleague had claimed to have seen the frog I was searching. This elusive frog had a unique habit: it bred inside bamboo. The narrow path we were on led to Thadiyandamol, Coorg’s highest peak, about 1700 m in elevation. It is a popular trekking route often overrun with trekkers and tourists, but when we got there in the evening, there was nobody around. Presumably, the incessant rain and hordes of leeches had kept even the most enthusiastic trekkers at bay. Darkness set in early and the clouds began to slowly open up. As we were passing by a stream, we heard a “keee-kit-kit-kit-kit” call. I knew immediately that we had found our quarry. It was the call of the Ochlandra Reed Frog, Raorchestes ochlandrae.
The long journey
Locating the frog was easy: the sound came from inside a bamboo clump with a small opening. I carefully split the bamboo internode open with a knife, and not only was the frog inside, but there were nine eggs too! The frog was discovered in 2007 by Dr. Gururaja and his colleagues, who were intrigued by a call that came from within bamboo. Having cut open the bamboo, they had found this frog and immediately described it as a new species to science. Very little was known about the frog, apart from the fact that they breed inside bamboo. How do they end up inside the bamboo? What are they doing inside? Who is making the holes in the bamboo? These were some of the obvious questions that were lacking clear answers.
Incidentally, I had arrived at these same questions in a contorted way. Since 2009, I had started observing frogs, and one night, I was privy to an incident that somewhat changed my thinking of frogs and dictated the next four years of my academic life. I was heading to the field station in Upper Kodayar within the Kalakad Mundanthurai Tiger Reserve, with my colleagues Dr. Ganesh and Prashanth MB. To get there, we had to cross a bridge across River Manimutharu, with a few trails breaking off from the bridge into the forest. Walking into one, I heard a strange call, and looking for its source, saw an adult male calling from a bamboo stalk. I grabbed my camera and began recording. As we stood watching, the frog did something that left us all in awe – it squeezed itself into the bamboo stalk via a small opening, with great difficulty! We had set eyes on the White Spotted Bush Frog (Raorchestes chalazodes).
After we saw the frog enter the bamboo, we started discussing amongst ourselves, and several questions began dancing wildly in our heads. Over the next couple of months, I continued to cut open bamboo and see what the frogs were doing inside. It became clear that the frogs were breeding inside these bamboo clumps, often known as reeds.
Discovery of a new behaviour
Eventually, I ended up at the National University of Singapore, and continued synthesizing my observations with inputs from David Bickford, my supervisor. We now had information on the number of eggs laid, how long they take to develop, what time of the year they breed, and what kind of bamboo they prefer breeding in. When we compared the behaviour of R. ochlandrae and R. chalazodes, it became evident that the two were showing exactly the same behaviour – the frogs would enter the bamboo via a small opening made by an unknown organism; lay eggs that developed directly into frogs without a free living tadpole stage; and the adult frog sat with the eggs, perhaps taking care of the young ones. All this was indicative of parental care behaviour, which was never properly studied in India. Having now gathered sufficient evidence, we realised that we had discovered a novel reproductive mode.
Reproductive modes in frogs and toads are classified based on the egg deposition site, the kind of egg (direct developing or tadpole metamorphosis), and whether or not parental care exists. The global diversity of reproductive modes currently stands at 44, and fish have around 20 modes.
Why breed inside bamboo?
I attempted to find out what these frogs do inside bamboo, by studying the behaviour of R. chalazodes. These frogs measure 20.6–25.2 mm from snout to vent. They get into bamboo with some difficulty, indicating that they are doing it with some purpose and not a random “Oh, I am here, let me breed” thought. Further, frogs chose internodes only if the opening was at the bottom end and not at the top; this was because a top opening would let water flow in and drown the eggs. The eggs were about 5 mm diameter and laid in sets of up to eight. Being transparent, one could see the embryo developing. With intensive study, I determined that the temperature inside the bamboo was on an average 2 °Celsius cooler than outside and the relative humidity was almost always 100%. These appear to be ideal conditions for direct developing eggs, which do not require free-flowing water but need ample moisture to hatch. So it made sense that male frogs found these holes on the bamboo, entered them, and called from inside to attract a mate.
Why parental care?
Looking deeper into what has already been said, I found Prof. EO Wilson’s book ‘Sociobiology’, written in 1975, to be a treasure. He attributed that life history strategies such as parental care evolved in amphibians because of four key drivers: situations where the frogs occur in stable and structured environments; the presence of unusually high stress levels in any given habitat; when frogs are dependent on scarce or specialised food resources; and lastly, face considerably high predation pressures. Did both R. chalazodes and R. ochlandrae evolve to breed inside bamboo driven by the forces highlighted by Prof. Wilson? I tested this on R. chalazodes and found that the males care for the eggs by attending to them and guarding them. When I experimentally removed the parent from the eggs, the eggs died, primarily because other males of the same species came and ate the eggs before starting to call from inside the bamboo. This was a unique discovery which opened up many more questions.
Who makes the holes?
The answer to this question became evident in the many years we spent doing field-work. As it turned out, Dr. Ganesh, with over three decades of field experience, was able to deduce this. While working in Kalakad Mundanthurai Tiger Reserve, he had heard a rare squirrel, the Nilgiri Striped Squirrel (Funambulus sublineatus), nibbling on bamboo. So we sat and observed the squirrel for a month, and were able to confirm that it was indeed the squirrel creating holes in the bamboo. We further supported it by observing bite marks on the bamboo, typical of a rodent. Why do these squirrels nibble on the bamboo? We do not know yet. But the frogs are somehow adept at finding these holes and entering them. Interestingly, the squirrel, the frog, and the bamboo are rare and endemic to India. All three of them are likely in danger of extinction because bamboo of the genus Ochlandra, which grow along streams, are used for the manufacture of paper and pulp. With bamboo often marketed as eco-friendly, the risk of over-harvest is high. Intervention measures to conserve these frogs could range from simply not harvesting bamboo during the frogs’ breeding season, to restricting the harvest of a particular sized bamboo.
Studies on the reproductive modes in anurans have come a long way. In the last few years alone, three new reproductive modes have been uncovered – one from our own backyard, the mud-packing behaviour of Nyctibatrachus kumbara. All these findings have shaken the very foundation of how we perceive amphibians. All these discoveries have had one thing in common: natural history observations, made by people sitting out there in the jungle and watching them. While amphibians are on the decline globally, in India, we are discovering such novelties. Natural history observations will certainly pave the way forward to understanding the world of amphibians better. I, for one, believe that the ground to be covered in unravelling natures’ mysteries will happen, and in that, anurans will lead us forward.
Over the years, I have encountered the Nilgiri Striped Squirrel in multiple places along the Western Ghats of Karnataka. The Ochlandra Reed Frog appears to be doing well, and subsequently, with help from colleagues, I was able to find this frog in multiple areas of Coorg as well as in Bhadra Wildlife Sanctuary. When you go out the next time and see the Ochlandra bamboo, keep your ears to the ground, for you may hear the faint call of the Ochlandra Reed Frog!