Island Odyssey – Lizards Of The Andaman Archipelago
While conducting research in the Andaman Islands, Nitya Prakash Mohanty found himself unpredictably enamoured by the islands’ endemic lizards and their countless quirks.
Photo: Karthikeyan Vasudevan.
Field biologists often have a favourite activity in their daily routine of sampling. A tiger biologist I knew liked to identify individual tigers from camera trap photographs at the end of the day, a herpetologist friend could not wait to log his day in his field notebook, and a diver buddy liked nothing better than to jump off the boat. As part of a population estimation exercise for my first project, I liked to capture lizards early in the morning. These lizards were more often than not the short-crested Bay Island lizards Coryphophylax subcristatus, endemic to the Andaman and Nicobar Islands.
The most abundant lizard in the forests of the Andaman Islands, the short-crested Bay Island lizard is not exactly a sight to behold. Often seen running up tree trunks, the diurnal reptile displays a limited range of colours; an olive green-brown male and a generally reticulated, dark brown female with or without blotching. Though, there is a fair bit of variation of patterns among the population, it is hardly noteworthy at first sight. Its cousin, the more recently discovered short-tailed Bay Island lizard Coryphophylax brevicaudus is an improvement in the colour department, with orange-brown to reddish-brown individuals. While the short-crested lizard is found in most forest types, even in littoral forests close to the sea, the short-tailed is restricted to dense evergreen and semi-evergreen forests with closed canopies. Despite the ecological intrigue that these two sympatric species posed, by virtue of their morphological and behavioural features, they were little more than a variable to me at the onset of my research; their density, their weight and length, all small components of a larger study into which I was immersed.
Photo: Nitya Prakash Mohanty.
One cannot trap life in a datasheet. Soon enough, due to their sheer abundance and hence, easy observation in the field, the lizards piqued my curiosity. When my colleague elaborated on the lifestyles of these two species of lizards, some known, some unknown to science, I was hooked. What intrigued me most was not their activity during the day, but their remarkable behaviour at night. Found perching on tree trunks by day, both species slept on saplings by night.
It was time to delve deeper to find an answer to that ubiquitous science-FAQ – “but why?”
The lizards made it easy by their sheer numbers, and we were able to observe as many as 501 lizards at their individual sleeping sites. Various structural parameters of the perch and its surroundings, microclimatic factors such as temperature and humidity, plus body size of the lizards were on our ‘to-measure’ list. To my amazement, 96 per cent of the lizards were found perching on flimsy plants – seedlings, saplings, even fallen branches. Even the ones on trees were seen roosting on swaying terminal branches. We conjectured that this behaviour likely helps dozing lizards detect predators slithering up their perch and allows them time to escape, or possibly discourages heavy predators to attempt a climb in the first place.
By the time I picked up the last adult male in a forest in Little Andaman Island on a sultry night, I could picture a sleeping lizard every time I closed my eyes. A symptom, I am told, most common to people in love. A nap of five minutes would bring me a sub-adult short-crested lizard, 1.6 gm. in weight, 12.6 cm. in length, perching horizontally on the leaf of a fish-tail palm sapling, with its head away from the main trunk, ready to jump down a height of 107.3 cm. to the ground, or 40 cm. to the nearest plant. Such lizard delusions were kept in check by staying well-caffeinated and restricting sampling to short periods of time, in the company of two field assistants. All this for the lizards that had aroused little interest in me earlier.
Photo: Nitya Prakash Mohanty.
Creatures of habit
While the sampling frenzy was still on, one rainy night, I found a male short-crested lizard perched on a Korthalsia palm next to the dining area at my base camp, sheltered from the stinging rain drops by a fallen leaf. I could not help but check the same plant the next evening when it rained. Sure enough, there it was. This was not entirely a surprise, as few researchers at the base camp would tell me, from time to time, how a particular individual would visit their cottage to sleep on the clothes line every night. Though they knew the individuals more or less by size and colour, there was only one way to be sure. So, the next evening, I set out with a bottle of blue nail polish. An hour later, 10 short-crested lizards were flaunting sober blue roman numerals on their flanks. Combined with their protruding throat pouch and distinctively large crest on the neck, the males were a class act. I marked the original sleeping site where I had caught them and left them alone for a day. After a week of repeated nocturnal visits, evidence of some level of site fidelity became clear in all stages of short-crested lizards. An adult male (marked VI) and two juveniles (III and VIII) returned to their original site with such precision that one might have presumed they had not moved all day!
It was only logical then to track their shenanigans by day. Favourite perches, high voltage territorial fights, vigorous sexual displays replete with push ups (yes, they do that) and head bobbing were on display, in stark contrast with their nocturnal behaviour. While the lizards tended to sleep on thin, flimsy perches at night, they found suitable platforms on rigid tree trunks by day. Spotting insects in the leaf litter from their vantage point, they would scurry down in a flash, only to return to their favoured perch faster than one could remove the lens cap from the camera. Their escape strategy on either side of sunrise was equally interesting. At night, when disturbed, the lizards would drop to the ground and scatter. By day they would shoot up tree trunks to avoid capture.
Photo: Karthikeyan Vasudevan.
Similar, yet different
If the repertoire of behaviour was not enough to lure a researcher, the ecological differences between the short-crested Bay Island lizard and its cousin, the short-tailed Bay Island lizard would surely do the trick. The short-crested, with its longer and stouter tail, generally uses higher perches than the short-tailed during the day. Further, sexual differences in the short-tailed lizards are less pronounced. How the two closely related species thrive in the same forest is still not completely understood.
After days spent attempting to survive yet another hour in the forest, the lizards mate to produce a pair of eggs and bury them in the vastness of the islands of the Andaman and Nicobar archipelago. Isolated on one island or the other, my two team members and I, were most delighted to witness the lizards return our curiosity about them in a most courteous manner. As we set out each morning, the lizards of the neighbourhood would come running towards us, just to gape at the sight of three individuals of a different species. Our unfamiliar presence barely bothered these children of isolation.
As a researcher I tend to treat my subjects fairly dispassionately, as sources of data. But, for the first time these lizards had become much more than that for me. Their behavioural complexities, uncertain phylogeny and affinity for springing surprises has turned them into ‘individuals’ for me. By the time we had located over 400 individuals in the course of our sleeping-site study, I was fairly certain that no two individuals slept on the same plant. Then, one evening I found two short-tailed lizards on different branches of the same plant. A couple of evenings later, I found an adult female and a sub-adult female short-crested lizard sleeping on the same leaf. The next evening, amidst a light drizzle, I came across two adult females on top of one another!
People say that over time researchers develop characteristics of their study species. After three seasons of field work in their midst, I most certainly cannot extend the skin of my throat to signal to my conspecifics, or for that matter manage as many pushups as a short-crested lizard. Fortunately, however, I can regard them the way they inspect unfamiliar individuals, such as us, in their company – with curiosity.
An islanded naturalist
Field research on island lizards has taken me to numerous breathtaking locations, of which there is no dearth in the Andaman Islands. The evergreen forests of Mount Harriet National Park, close to Port Blair, provide a window into the multitude of endemic birds and reptiles. An hour’s drive away is Munda pahad at Chidiyatapu, the southern tip of South Andaman Island. A short trek through these woods can help a birder tick several endemic birds off their list, such as the Green Imperial Pigeon and the Andaman Serpent Eagle. Off the south-west corner of the Island, lie 15 small islands constituting the Mahatma Gandhi Marine National Park. A ferry ride through the azure blue waters of the park can be beyond rewarding. Snorkeling off Jolly Buoy Island offers a glimpse into fascinating reef life. A trip up north opens up opportunities for mangrove creek exploration in the Middle Andaman Island. On a good day one might see most of the eight species of kingfishers found in the Islands. Further north lies the Saddle Peak National Park, which poses the challenge of a steep trek, through dense forest, to the highest point on the island. And no trip to the Islands is complete without a trip to Little Andaman Island. Virtually all the beauty of the Andaman archipelago, including pristine beaches and ancient evergreen forests, are encapsulated within this wonderland.
Author: Nitya Prakash Mohanty, First appeared in: Sanctuary Asia, Vol. XXXV No. 10, October 2015.