Bisle, in Sakleshpur taluk of Hassan district, is a quaint village nestled amidst the Western Ghats. Smack in the middle of this small village is a community hall where over 30 of us had assembled. We call ourselves the ‘Bisle Frog Team’ and we meet every year in July. It is a first of its kind citizen engagement activity where frog lovers get together and look for frogs. Post lunch, each of the participants had completed the customary introductions. Everyone had to raise their voices to be heard, thanks to the rain pounding hard on the asbestos roof. Everything was damp. The situation was quite a parable for what frogs would be doing at night – raising their voices to be heard over the cacophony of other chorusing frogs.
Ramya, a colleague of mine, who had stepped out for a moment, returned looking delighted, holding out her phone. She had clicked pictures of a gorgeous frog that was sleeping on the door – Rhacophorus lateralis! We jumped in excitement and stormed out to grab a glimpse. The frog was fast asleep. Hands and feet tucked in, it looked almost like a leaf stuck on a wall. It was only noon and we had already sighted our first frog. It could only get better, as the little sunlight filtering through the cloudy sky was snuffed out by another torrential downpour.
Lost and found
Rhacophorus lateralis is known by more common names than the number of locations it’s been reported from. Boulenger’s Tree Frog or Small Gliding Frog or Small Tree Frog or Winged Gliding Frog – all of them aptly describe the frog and its habit. Described by Boulenger in 1883, this creature was lost to science until the late 90s, when a team of researchers working in Coorg collected it. The species was described by Alfred Boulenger, based on a specimen passed on to him from Col. Richard Henry Beddome from a locality called ‘Malabar’. It now refers to Kerala and perhaps was the reason why no one found this frog for so many years! Since the re-discovery, the Small Gliding Frog is locally abundant and is found across Coorg and parts of Wayanad in Kerala, in and around coffee estates and estate bungalows.
Nightfall came early and we stepped out to brave the downpour and leeches to count frogs. Right beside the community hall is a pond. A small bund helped to store water, and quite naturally, we went there looking for frogs. The pond at its deepest point was merely waist-deep and we could easily wade through the shallow edge. But, the heavy rains had brought in a lot of silt that made wading difficult. Dr. Gururaj led the group and we reached the vegetation around the pond. In five minutes, I had had my fill of the Small Gliding Frog. Over forty individuals were perched on the vegetation in and hanging over the water. The frog is green overall, with two bright green bands on either side, starting from the tip of the snout, all the way to the vent. Their soft ‘tuck-tuck-tuck’ calls gave the whole place a surreal ambiance. The rain gods had some mercy on us and the pounding rain ceased momentarily. The flash from the camera made the frogs turn brown, suddenly. The otherwise green frogs appear to respond to flashlight and turn brown. They also do this when they jump on to a brown twig. Why they do so is something we do not yet understand.
On leaves, I was able to witness a unique behaviour that was on my must-see list. The Small Gliding Frog, which perhaps may never glide, is an apt candidate for yet another common name – the Purse Making Frog. Since the frog’s rediscovery, numerous researchers have had their eyes tuned on the frog. In an important natural history contribution, Dr. Biju, also known as the ‘Frogman of India’, studied the behaviour of this tree frog. The male frogs call to attract females and the female picks out the male she wants to mate with. Later, she positions herself on a leaf and lays out her spawn of eggs numbering around 40-70. The male abandons her, and the female then re-positions herself on the petiole of the leaf and starts working her way downwards, folding the leaf and sealing the two edges with a sticky gel. This laborious process of just making the purse nest takes up to 30 minutes. Many charged-up males try to sneak their genes into the nest and form a ‘mating ball’ around the mating pair, rendering the process impossibly difficult.
Why take all this trouble to build a nest?
Amphibians exhibit a remarkable diversity of reproductive strategies. Broadly, these strategies have been categorized into reproductive modes based on where the frogs lay their eggs, whether or not the eggs hatch into tadpoles or directly into froglets, and the kind of eggs laid (i.e. in a gel mass or as a foam nest) etc. Frogs and toads alone exhibit 42 different reproductive modes, the second most diverse in all of vertebrates. Laying eggs on leaves is a common strategy among numerous tree frogs in the frog family Rhacophoridae. These arboreal frogs live on trees and are commonly called the Gliding Frogs. All members within the genus Rhacophorus deposit eggs in a gel or foam nest on leaves hanging over water, but only the Small Gliding Frog takes the trouble of ensuring that the eggs are locked in a nest. Such behaviour is not random, and certainly has an evolutionary advantage.
Prof. Edward O. Wilson, called the ‘Father of Biodiversity’, suggests four main reasons why frogs invest in some form of care for eggs after they are laid. Predation is foremost among them. Indeed, researchers have observed that such leaf nests provide young embryos protection from predators. In Bisle, we did not see any predator emptying the nests of the Small Gliding Frog. The frog eggs hatch as tiny tadpoles and wriggle out of the gel nest. When the time comes, the jelly breaks, and the tadpoles drop into the water below. Almost immediately, they swim to safety. The tadpoles now have a higher chance of survival.
The froglets then hop out of water. They already have bands on their limbs and spots on their backs. They almost look like a cross between a mini Tiger and a Spotted Deer!
Two nights of frog-watching vanished in the blink of an eye, and we returned to our urban lives rather reluctantly. After a year, I serendipitously had an insight into what might be driving the Small Gliding Frog to build nests. While working in Coorg in June 2016, I was wading through a small pond in a private property and noticed a Checkered Keelback stalking a Small Gliding Frog. With excruciating caution, the snake made its move, only to miss. A few moments later, I stumbled upon what looked like a Ceylon Cat Snake feeding on something. On closer inspection, it turned out that the snake was gorging on the eggs of a Small Gliding Frog. The nest, however, was already damaged, and the eggs were dead. Witnessing this predation gave me a hint as to what predators may lurk in the bushes: vertebrates, apart from numerous insects. For the frog, making eggs is an expensive affair in terms of the energy it needs to spend. It makes sense for the frog to put in some effort to ensure the safety of the eggs and this would clearly render an evolutionary advantage.
Unique but already endangered
This unique behaviour went unnoticed for several years, as the frog itself was lost to science. Now that it has been re-discovered, we are slowly inching forward to knowing more about the frog. The frog is known from very few locations from the Western Ghats, and the habitat in general continues to degrade. Listed as Endangered on the IUCN RedList, this frog’s future is in limbo.
I first chanced upon this dainty frog along roadside shrubbery near Banasura Dam in Kerala. The frogs appeared to be common in the adjacent coffee bushes. Subsequently, I saw them in Bisle, where they were locally abundant and seemed to be doing well. The population of these frogs in Coorg is rather enormous. My colleague Vidisha counted over 50 individuals around a pond in a resort in Madikeri. This species is also found in numerous coffee plantations and around man-made ponds in Coorg District.
Have the frogs given up on pristine forests and are adapting to what little habitat is left? Perhaps, such modified habitats are the ones they have always been found in? We really don’t know. So, when you are out in the forests of the Sahyadris this monsoon, take your torch and sneak out at night. I hope you spot this elegant frog caring for its eggs by packing them in a purse.