Snakes – Why No Legs?

One of our members, Jonathan Tan, recently wrote an essay on why snakes have evolved to be legless. We’ve invited him to share it here to help our readers better understand their fascinating evolutionary history. 

Disclaimer: our understanding of the evolution of snakes is itself continuously evolving, so this essay may contain points of contention. 

What causes a new trait to evolve in an organism? When a character becomes fixed, it is usually because it provides a selective advantage that increases that organism’s fitness over competitors’. Many characters also affect fitness only within particular niches, not universally; evolving wings for instance, would probably be less useful in the water than on land.  But tracing the original selective advantage of characters is not simple, as they can subsequently be adapted and repurposed for completely different uses such as how the wings of penguins are used as flippers. This is especially so for taxa with a wide variety of habitats and lifestyles, such as snakes. Today, snakes can be found in aquatic (both freshwater and marine), terrestrial, fossorial, and even arboreal environments. The defining character of snakes to most people is often their lack of legs. But having diversified extensively into so many different niches, the adaptive advantages, selection pressures, and environment that first resulted in their evolution of limblessness can be difficult to figure out. To do so, we must first identify the original conditions in which the very first snakes lived.

What sort of habitat did the first snakes live in?

There are two main hypotheses for the form of the last common ancestor of snakes: a terrestrial burrower, or a marine swimmer[1]. Phylogenetic reconstruction using snake fossils as well as extant species can tell us which is likelier. A reconstruction[2] found it certain that the ancestors of both crown group and total group snakes were terrestrial, but not necessarily fossorial. Analysis [1] of the inner ear vestibular shapes of modern snakes correlating them with habitat type led to the deduction that both Dinilysia patagonica, a Cretaceous era snake sister to all modern snakes, as well as a hypothetical ancestor of all modern snakes had burrowing lifestyles (Figure 1). Furthermore, most basal snake clades are burrowers[3], as can also be seen from Figure 1. Evidence for the fossorial origins of snakes can also be found in the morphology of other limbless squamates. There are two main ecomorphs: the short-tailed (tail at most half body length) and long-tailed (tail about 1.5 times body length). Short-tailed limbless squamates such as amphisbaenians and legless skinks are all burrowers; long-tailed ones such as legless anguids all live on the ground surface[4]. Snakes fall morphologically into the former group, making it highly likely that the ancestral snake was also a burrower, and that its non-fossorial descendants retained this body plan when they recolonised surface niches. Other parts of snake anatomy also suggest their fossorial origins. Snakes have unique eye structures[5] and optic nerves[6] that are the result of the restructuring of original squamate eyes[7]. This secondary re-evolution of visual acuity would be expected if snakes descended from a fossorial ancestor, as most limbless tetrapods have poor vision with reduced eyes due to their subterranean lifestyles[7]. The loss of external ear openings and inability to hear sounds above 1500 Hz in snakes also correlates with the poor hearing of other fossorial limbless squamates compared to surface dwelling forms[8]. Both phylogenetic evidence and morphological comparisons with other limbless squamates thus suggest snakes first evolved in a fossorial habitat.

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Figure 1 Phylogeny of snakes (nested within squamates) showing habitat type and corresponding vestibule shapes[1]. E indicates the hypothetical common ancestor of crown group snakes (70.1% probability burrowing type), F indicates D. patagonica (93.4% probability burrowing type). The more basal snake clades, represented by R. caecus and T. jamaicensis, and A. scytale, are burrowers.

Why did snakes evolve to live in fossorial habitats?

What might have made fossorial habitats such promising environments that snakes evolved to occupy it? Firstly, they provide excellent concealment and protection from predators that lack similar burrowing abilities[9]. A surface predator would be unable to spot snakes concealed in the soil or leaf litter, and if it were to dig for them, a snake could still escape by quickly burrowing away or going deeper. Even today, save for non-fossorial snakes, almost all limbless tetrapods such as amphisbaenids or caecilians burrow in soil or take shelter in crevices for safety[7]. Fossorial habitats also contain a wide variety of small prey items (e.g. rodents and invertebrates) which seek refuge in leaf litter and subterranean environments[9], making it attractive for small carnivores such as snakes. Although many snakes of today take on prey larger than their own heads due to their highly kinetic skulls[9], ancestral state reconstruction[2] suggests the first snakes targeted smaller prey.  Fossorial snakes of today continue to specialise in eating small animals such as rodents, other snakes, or in the extreme case of scolecophidians, ant/termite larvae[10]. Finally, the opportunity to exploit a new niche in the face of competition from other squamates may also have driven snakes underground. Competition with closely related taxa often drives evolution of novel characters to occupy new niches[11], and sometimes in distinct, determinative patterns. For instance, the very same combination of different ecomorphs evolved in anoles independently on four separate Caribbean islands[12]. Similarly, where there is an empty fossorial niche, a limbless squamate is likely to evolve, an event that has happened at least 20 times[4]; even small isolated patches of new fossorial habitat can give rise to novel limblessness evolution, such as the Calyptommatus lizards endemic to the Sao Francisco sand dunes[13]. The presence of so attractive an unfilled niche meant that snakes adapted to fill it; and in the process they became limbless.

How does limblessness help in fossorial habitats?

So how did limblessness benefit snakes when they were adapting to fossorial habitats? Primarily, this had to do with ease of movement. Serpentine body plans, characterised by elongated bodies and limblessness, are very effective for movement through dense herbaceous foliage and loose soil[9]. Fossil evidence shows that snakes became elongated before losing their legs[14]. Elongation – reduction of body diameter to length ratio –  allowed them to access a larger proportion of crevices while expending less energy trying to squeeze through[7]. When they then lost their limbs, snakes further reduced their effective body diameter, improving their ability to hunt for prey in narrow tunnels and small cracks, as well as flee from predators into the soil/leaf litter or find shelter amongst rocks. Elongation also preadapted them to evolving reduced limbs, as it provided the additional vertebrae necessary for lateral undulation to replace walking and the need for functional limbs. Lateral undulation may be more energy efficient than quadrupedal movement because there is no need to lift the body against gravity[15]; retaining extraneous legs that affected the body’s streamlining would also have reduced the efficiency of this new form of movement. Lateral undulation being common in limbless tetrapod lineages (Table 1) which are almost all fossorial, it likely had strong functional advantage in fossorial habitats where there is little space for limbs to work. With legs having lost their main function to be replaced by lateral undulation, even becoming a hindrance in tight spaces and when slithering through substrate, limblessness would have helped snakes better occupy their fossorial niche.

 

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Table 1 Locomotion methods of limbless vertebrates. Note that all the tetrapods share lateral undulation as a form of movement[7]

Conclusion

Limblessness evolved as an outcome of the adoption of a previously unfilled fossorial niche by early snakes, giving them an even greater adaptive advantage in foraging and avoiding predators in an environment where already food was abundant and predators few. But while this accounts for the initial evolution of limblessness, it does not answer why many modern snakes continue to be limbless even as they diversified into new habitats, as they clearly retain the ability to re-evolve legs (e.g. Tethyan snakes from the Cretaceous[16] ). Instead, snakes seem to have evolved a variety of means to overcome the limitations of being limbless in non-fossorial habitats, such as rectilinear motion to climb trees, or sidewinding in deserts[9]. Perhaps there are secondary benefits to limblessness in these new niches, such as camouflage or stealth; or legs on such an elongated body may just be ineffective as a mode of locomotion. While we can understand under what conditions they lost their legs, why losing them was beneficial at the time, and even the process of losing them relative to other traits, we still do not fully understand why they continue to lack them. For now at least, snakes will continue to remain just a little bit of a mystery.

References

[1] – Yi, H. & Norell, M. A. (2015) The burrowing origin of modern snakes. Science Advances. 1 (10), 19 March 2017. Available from: http://advances.sciencemag.org/content/1/10/e1500743 [Accessed 19 March 2017].

[2] – Hsiang, A. Y., Field, D. J., Webster, T. H., Behlke, A. D. B., Davis, M. B., Racicot, R. A. & Gauthier, J. A. (2015) The origin of snakes: revealing the ecology, behaviour, and evolutionary history of early snakes using genomics, phenomics, and the fossil record. BMC Evolutionary Biology. 15 (87), 19 March 2017. Available from: http://bmcevolbiol.biomedcentral.com/articles/10.1186/s12862-015-0358-5 [Accessed 19 March 2017].

[3] – Zug, G. R., Vitt, L. J. & Caldwell, J. P. (2001) Herpetology: an introductory biology of amphibians and reptiles. 2nd edition. San Diego, CA, Academic Press.

[4] – Wiens, J. J. & Brandley, M. C. (2009) The evolution of limblessness. In: Hutchins, M. (ed.).Grzimek’s Animal Life Encyclopedia. Internet edition. Farmington Hills, Michigan, Gale Cengage.

[5] – Walls, G. L. (1942) The vertebrate eye and its adaptive radiation. Bloomfield Hills, Michigan, The Cranbrook Institute of Science.

[6] – Northcutt, R. G. & Butler, A. B. (1974) Retinal projections in the northern water snake Natrix sipedon sipedon (L.). Journal of Morphology. 142 (2), 117-135.

[7] – Gans, C. (1975) Tetrapod limblessness: evolution and functional corollaries. American Zoologist. 15 (2), 455-467.

[8] – Wever, E. G. (1967) Tonal differentiation in the lizard ear. The Laryngoscope. 77 (11), 1962-1973.

[9] – Parker, H. W. & Grandison, A. G. C. (1977) Snakes – a natural history. 2nd edition. Ithaca, New York, Cornell University Press.

[10] – Parpinelli, L. & Marques, O. A. V. (2015) Reproductive biology and food habits of the blindsnake Liotyphlops beui (Scolecophodia, Anomalepididae). South American Journal of Herpetology. 10 (3), 205-210.

[11] – Schulter, D. (2000) The Ecology of Adaptive Radiation. Oxford, United Kingdom, Oxford University Press.

[12] – Losos, J. B., Jackman, T. R., Larson, A., de Queiroz, K. & Rodriguez-Schettino, L. (1998) Contingency and determinism in replicated adaptive radiations of island lizards. Science. 279 (5359), 2115-2118.

[13] – Wiens, J. J., Brandley, M. C. & Reeder, T. W. (2006) Why does a trait evolve multiple times within a clade? Repeated evolution of snakelike body form in squamate reptiles. Evolution. 60 (1), 123-141.

[14] – Martill, D. M., Tischlinger, H. & Longrich, N. R. (2015) A four-legged snake from the Early Cretaceous of Gondwana. Science. 349 (6246), 416-419.

[15] – Chodrow, R. E. & Taylor, C. R. (1973) Energetic cost of limbless locomotion in snakes. Federation of American Societies for Experimental Biology. 32, 422.

[16] – Leal, F. & Cohn, M. J. (2016) Loss and re-emergence of legs in snakes by modular evolution of Sonic hedgehog and HOXD enhancers. Current Biology. 26 (21), 2966-2973.

Herping Ubin

Today was the HSS’ first Herp Walk held on Pulau Ubin! Previously, night walks had been held in collaboration with the Vertebrate Study Group (VSG) branch of the Nature Society as part of Pesta Ubin 2016, and HSS members also helped survey for herptiles during BioBlitz Ubin in December last year. Given the rich herpetofauna that we observed during those events, it was a no-brainer to have our first Herp Walk of 2017 at everyone’s favourite kampong getaway. However, we were also heartbroken to learn that the recent oil spill had now affected the mangroves of Ubin; more about this towards the end of the post.

As we started off on the walk, we were greeted by two of Ubin’s iconic Oriental Pied Hornbills (Anthracoceros albirostris) just next to the jetty! These charismatic birds were once extinct from Singapore, before making a return through natural dispersal from Johor; Ubin was their first foothold. It was good to see them still doing well.

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Oriental Pied Hornbill (Anthracoceros albirostris)

Our first herp of the day proved to be a male Sumatran Flying Dragon (Draco sumatranus)! This amazing gliding lizard was high up a coconut tree, flashing its yellow dewlap to ward off rival males. As we scanned the trunks of the neighbouring trees, we spotted a Green Crested Lizard (Bronchocela cristatella) and two more Flying Dragons, basking in the bright sunshine. The Green Crested Lizard, like its introduced competitor the Changeable Lizard, is able to change colour; depending on its mood or need for camouflage, it can switch between black and green.

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Green Crested Lizard (Bronchocela cristatella
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Sumatran Flying Dragon (Draco sumatranus)

It wasn’t long before one of our participants spotted the first snake of the day: an adult Oriental Whip Snake (Ahaetulla prasina), probably the most commonly sighted snake in Singapore. A minute later, a juvenile Oriental Whip was discovered in a bush just next to the adult! Instead of being neon green, young Oriental Whips are a dull brown, perhaps so that their very slender bodies can better resemble small twigs.

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Adult Oriental Whip Snake (Ahaetulla prasina)
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Juvenile Oriental Whip Snake (Ahaetulla prasina)

As we moved on to the mangroves, the fiddler crabs (Uca sp.) were out in force, with dozens of males flashing their bright orange claws to defend their territories and attract females. Mangroves are important habitat for lots of animals including reptiles, such as monitor lizards, snakes, and crocodiles. The Restore Ubin Mangroves project, which aims to promote natural regrowth of the mangrove forests by making the hydrography more favourable for new seedlings to grow, will thus hopefully also create more habitat for these herps to flourish!

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Male Fiddler Crabs (Uca sp.)

Many birds made an appearance throughout the walk, including these two bright balls of energy: an Orange-bellied Flowerpecker (Dicaeum trigonostigma), and a Crimson Sunbird (Aethopyga siparaja)! The former was feeding on the berries of the Singapore Rhododendron (Melastoma malabathricum), also known as Sendudok, while the latter flitted about looking for flowers to suck nectar from. These birds are important to forest ecosystems as they disperse the seeds of plants and help pollinate their flowers.

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Crimson Sunbird (Aethopyga siparaja)
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Orange-bellied Flowerpecker (Dicaeum trigonostigma)

We ended off the walk with a sighting of the introduced Changeable Lizard (Calotes versicolor), and another Green Crested Lizard (Bronchocela cristatella). Both these species have similar niches, though the more aggressive Changeable Lizard seems to have pushed the Green Crested out of parkland and urban areas. Ubin however seems to be one of the few places where both can be easily spotted, possibly due to the unique mix of secondary forest and kampong habitat found throughout the island.

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Bitter rivals: Changeable Lizard (Calotes versicolor) and Green Crested Lizard (Bronchocela cristatella)
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Guides and participants from today’s walk

After the walk ended, most of the guides headed over to Chek Jawa to take a look at the impact of the oil spill. Many of the mangrove roots were covered in sticky black oil, though most of the mudflat seemed clean. There were many workers deployed to clean up the oil that had evaded the absorbent booms just offshore, as well as some volunteers, all wearing protective body suits, boots and gloves. We also received word from our friends at NUS Toddycats that were helping with the cleanup, that a nationally Critically Endangered Keel-bellied Whip Snake (Dryophiops rubescens) had been found coated with oil. Gently retrieving the snake, we rushed it back to the NParks office on Ubin where it was slowly cleaned by staff and left to recover before release. Note: snakes should not be handled except by trained experts, and only where it is necessary and does not harm the snake’s welfare. Do not try this at home!

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Keel-bellied Whip Snake (Dryophiops rubescens). The grimy appearance of its scales is due to oil from the spill
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The snake being cleaned by NParks staff and HSS volunteer Noel Thomas
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Oil cleaned from the snake

 

 

 

 

 

 

 

 

 

 

As the example of the Keel-Bellied Whip Snake demonstrates, oil spills can affect a very wide variety of wildlife; even an arboreal snake like this one may accidentally stumble into oil that has been washed up onto mangrove trees. If we are to protect our biodiversity and herptiles from such threats, we need to be well-prepared to ensure that the oil never reaches the shore, or even better, doesn’t spill into the sea in the first place.  Given the large role that oil has in our economy, this will almost certainly not be the last such disaster. Hopefully going forward, this tragic incident will teach us the lessons needed to better handle future incidents and minimise the impact on our precious wildlife.

Of Vipers and Vivipary

Having had to cut short the previous walk in August due to rain, we were delighted to have clear weather for our latest walk in September, once again at the MacRitchie Treetop Walk! We also welcomed two members of the Little Green Men, Sarah and Frances, to join us on our walk; if you’re interested in making a difference for the environment however you can, try contacting them!

img_3525Even before all our participants had arrived, our dedicated spotter Wei Yang found the first herp of the day: a beautiful Oriental Whip Snake (Ahaetulla prasina)! One of the most commonly sighted snakes in Singapore, it ranges widely into parks and gardens to feed on small lizards like geckoes and skinks. With their brilliant green colour and sinuous bodies, they can be easily mistaken for vines or climbing plant tendrils. Mildly venomous, this snake is harmless to humans though it can bite when provoked. As Sankar explained, they are viviparous, meaning they give birth to live young! The word “viper” in fact is derived from “vivipary”, as vipers are amongst the snakes that have this trait.

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Say cheese!

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As we trekked deeper into the forest,  several Many-lined Sun Skinks were seen basking in patches of sunlight that managed to penetrate to the understory. We also found many weird and wonderful arthropods, such as the caterpillar above! The fact that it was bristling with spines that may also contain venom would have been difficult to swallow for many a bird. img_3541

We were fortunate to have Sean Yap, a member of the Entomological Network of Singapore (ENSING) as well as HSS, to help us identify these strange critters found swarming about on a wooden railing. Apparently these are barklice (Order Psocoptera); harmless insects that feed on algae, fungi, and dead plant tissue that grow on trees, they help keep them clean of detritus!

img_3543We also stumbled across this cool-looking Flat-backed Millipede (Platyrhacus lineatus) with plates whose edges jutted out from the main body. This makes it difficult for predators to attack its more vulnerable underbelly.

pill-cockroachHerps aren’t the only animals that struggle with an image issue. Cockroaches are often hated for being pests that feed on our trash and spread disease. But our native cockroaches play an important role in the forest by feeding on dead organic matter and speeding up the recycling of nutrients! And some of them can be pretty adorable too, like the Pill Cockroach (Perisphaerus sp.) shown above! Who knew that cute cockroaches were a thing!

img_3552Having already trained their eyes with those small little invertebrates, one sharp-eyed participant spotted this Red-crowned Barbet (Psilopogon rafflesii) on a dead tree trunk! Restricted only to our mature forests, it may have been digging for insects or perhaps building a nest.

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At last, more herps! The Black-bearded Flying Dragon (Draco melanopogon) on the left was showing off its patagium, the flap of skin that allows it to glide between trees! If you look closely, you can see the rib bones that the lizard swings outwards to open up its wingsuit! This individual may have been displaying to another flying dragon to warn it to keep to away from its territory.

The lizard on the right is the elusive Yellow Striped Tree Skink (Lipinia vittigera), courtesy of our veteran elf-eyed spotter, Ing Sind. Small and nimble, it usually hides amongst the roots of epiphytes (plants that grow on other plants, usually trees, such as orchids) or in tree crevices, emerging to feed on small insects. Like many lizards, it is able to drop off its tail when threatened, and this one was in the midst of regenerating it. The tails of lizards often contain important stores of fat and contribute to maintaining its balance, so losing it, while not life-threatening, can be a major blow; so leave lizards alone, lest they inadvertently lose their head and lose their tail!

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While on the Treetop Walk itself, we spotted another species of gliding lizard, the Sumatran Flying Dragon (Draco sumatranus)! This one, probably a male, was flashing its yellow dewlap to warn off other males and perhaps show off to nearby females.

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Viper Number 1

We were lucky to meet not one, put two vipers on this walk! Both were male or possibly juvenile Wagler’s Pit Vipers (Tropidolaemus wagleri), coiled around young tree seedlings along the trail. These are ambush predators, lying in wait for prey such as small mammals and birds to wander past before striking with lightning fast speed and their forward-swinging fangs. With heat-sensitive pits on their snouts and blood-destroying haemotoxin, these are formidable foes to their enemies, and should always be treated with caution. As the vipers were located extremely close to the trail, well within striking distance of unwary hikers, we gently lifted them deeper into the undergrowth with a long stick; this was for their own safety as well as the safety of others.

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Viper Number 2

img_3113On the way back to the Ranger Station, we came across this blooming Tiger Orchid (Gramatophyllum speciosum)! The largest orchid in the world, it went extinct in the wild in Singapore over a century ago before being reintroduced by NParks in various parts of the island. Each individual plant only blooms every few years, with a massive stalk of up to 80 sweet-smelling flowers. We were fortunate to have come across this specimen while it was flowering.

©Herpetological Society of SingaporeNo Herp Walk is complete without a sighting of at least one monitor lizard, and true enough we found this large Clouded Monitor (Varanus nebulosus) basking in the sun! Unlike their bigger cousins the Malayan Water Monitors, Clouded Monitors are restricted to forests and feed mainly on insects and other arthropods they find by digging amongst leaf litter. The widespread presence of these lizards are a testament to how herps can coexist and thrive peacefully in our city. In fact, just the night before our walk, one of its cousins gained international fame by sprinting across the F1 race track during the qualifying rounds! And although that Water Monitor avoided being turned into a pancake, roadkills of these magnificent creatures are sadly all too common. If you’re a driver, slow down, especially near vegetated areas; it saves lives, both human and herp alike!

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As we always like to say, don’t Beware of Snakes (and herps); be Aware of them! Spread what you’ve learned to your family and friends too, so that we can continue sharing this little green dot with our herpy friends for generations to come!

Herp Walk: March for Macritchie

Our latest walk was held as part of March for Macritchie, a series of events organised by various groups in the nature community to raise awareness of the issues surrounding the Cross Island Line (CRL), and the wonderful wildlife that can be found in our Central Catchment Nature Reserve (CCNR). The CRL is a new MRT line that may be built under the CCNR forests, and as the soil investigation works for the project are expected to have a moderate level of impact on the ecosystem even with mitigating measures, we felt it was important that people knew about what was going on.

We started off the walk with a sighting of the Green Crested Lizard (Bronchocela cristatella), which nowadays is restricted only to our forest habitats. Once widespread even in urban parkland, it has now been displaced by the introduced Changeable Lizard (Calotes versicolor).

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Our next herp was a male Black-bearded Flying Dragon (Draco melanopogon), which was flashing its brightly coloured dewlap! This is a form of territorial display to warn off other males, as well as attract females. With the aid of folds of skin on their body called a patagium, these amazing lizards are able to flatten their ribcages to glide from tree to tree! A number of them were scattered on the tree trunks throughout our route.

 

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Just a few minutes later, we came across a Many-lined Sun Skink (Eutropis multifasciata) splayed out on some dead wood. These beautiful lizards love to bask themselves in patches of sunlight that reach the forest floor, hence their name. We would see a couple more of them before the day was done.

Stopping to take a break, our participants were treated to a storytelling session by Uncle Tony about the history of our rainforests! As the lead author of the Nature Society’s position paper on the CRL that proposed a skirting alignment that avoids passing through the CCNR, he had a wealth of knowledge to share about the value of the forests that would be affected.

12874602_10153982002708119_869340678_o.jpgWe were not the only visitors to the forest that morning, and a huge group of people (about 200) were also on a walk together to enjoy nature. Unfortunately, their large numbers meant that they were rather disruptive to the wildlife of the reserve, as the organisers often had to raise their voices to make themselves heard; the narrow trails, already full of people out for the weekend, were also badly overcrowded. NParks permission is required to bring in such large groups, with a maximum of 100 people within the same day. As our nature reserves already suffer from many other pressures inflicted by human activity, it is important that we follow these guidelines so as to safeguard the forests from suffering unnecessary damage. Hopefully, organisers of such events will be considerate so that everyone can enjoy our reserves.

As the large group was heading for the Treetop Walk, and we found it increasingly difficult to spot wildlife because of the sheer volume of people that were in it, we had to detour to an alternative route instead.

This proved to be a blessing in disguise, as we stumbled across a globally endangered adult Spiny Hill Terrapin (Heosemys spinosa)! The young of these beautiful terrestrial turtles have a heavily serrated carapace for added protection, but in adults these are greatly reduced. Found only in the lowland rainforests of Southeast Asia, they are sadly threatened by the illegal pet trade, making this find all the more special. The terrapin in question largely ignored us, ambling its way amongst our legs as it crossed the trail to move deeper into the forest.10392122_10153981897318119_2382677582909889725_n.jpg

1936457_10153981897348119_525959292808754456_n.jpgWe were also fortunate to spot a Red-crowned Barbet (Psilopogon rafflesii)! Feeding on various fruits, including some figs, this stunningly colourful bird almost seemed to be showing off for our participants’ cameras! Restricted to our mature secondary and primary forests, it is a prime example of the kind of wildlife that will be affected by the CRL project.

10609643_10153981897593119_8324369127986968670_n.jpg10553642_10153981897033119_7237823219565602217_o.jpgOne of the most fragile habitats in the CCNR are our freshwater forest streams, pristine rivulets of water that are host to an array of fishes found nowhere else in Singapore. We were able to spot some of these such as the Saddle Barb (Systomus banksi, left) and Spanner Barb (Systomus lateristriga, right), and their predator, a Snakehead (Channa sp.).

1474586_10153981897598119_8330704355394151678_n.jpgAs we arrived back at the Ranger Station for a break, a Yellow Striped Tree Skink (Lipinia vittigera) was there to greet us, scurrying about on the trunk and branches of a tree. A shy creature and one of the tiniest of our skinks, it is found only in mature forests and rarely seen.

1910617_10153981897633119_4448240626056082870_n.jpgTired but exhilarated, we headed back for the exit. But the herping didn’t stop there! We met an adorable baby Clouded Monitor Lizard (Varanus nebulosus, above right) busy digging through the soil and leaf litter for food! Although we had met several of its larger cousins throughout the walk, this one won everyone’s hearts. As it rummaged about with its oversized claws while flicking its forked blue tongue, someone quipped that he could sit there watching it all day long.
12779270_10153981897118119_6391926316970540943_o.jpgOur final herp of the day, sadly, was a dead Kopstein’s Bronzeback (Dendrelaphis kopsteini, left). A beautiful snake with an orange-red neck that it flares as a threat display, we suspect that it may have been killed by a human before being dumped along the roadside vegetation. Often misunderstood creatures, many snakes are persecuted and killed despite posing little threat to people. If you ever do come across one, leave it be and you’ll get along with one another just fine. If you encounter one in your house, you can always contact ACRES so that it can be relocated to somewhere safe.

All in all, it was a wonderful walk despite the large crowds, and we hope that it inspired our participants to find out more not just about herps, but the habitat they live in and how they can do their part to protect it for future generations to enjoy!

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Duelling Dragons and other Herps at Treetop Walk

The HSS held its second guided walk at the MacRitchie Treetop Walk, this time with Serin as our lead guide! We started off at the Venus Drive carpark entrance before making our way into the forest and embarking on an enjoyable 7km hike. And even before we entered the forest proper, we met our first herp of the day: a Common Gliding Lizard (Draco sumatranus) perched on a tree trunk! It proved to be a good omen, as we would see many more of these throughout the rest of the walk.

Our next herp was found along the Venus Drive stream, basking atop the root ball of an uprooted tree; a large Malayan Water Monitor (Varanus salvator). These big reptiles may look intimidating, but are harmless to humans and never attack unless provoked. In order to get a better angle to warm itself in the sunlight, it was hugging a small palm tree tightly.

Just a little upstream was the remnants of a large strangling fig that had been chopped down for safety reasons; and hiding in the crevices of the old trunk was a juvenile Many-lined Sun Skink! We also got a good look at the various native freshwater fish found in the stream such as the Pygmy Halfbeaks (Dermogenys collettei) and Common Snakehead (Channa striata).

As we continued up the trail, various weird and wonderful fungi caught our attention too. It was while examining a fungus growing on a tree trunk that one of our participants spotted our snake of the day, barely a couple of metres before his eyes: a White-bellied Rat Snake (Ptyas fusca)! This snake can grow up to 4 metres long, and feeds on rodents, frogs, lizards and other small animals.

Besides reptiles, there was plenty of other wildlife out and about. Several troops of macaques crossed
out paths as we headed towards the Treetop Walk, and we even spotted a trio of Lesser Dog-faced Fruit Bats (Cynopterus brachyotis) roosting on a tree! Birds such as the migratory Asian Paradise Flycatcher (Terpisiphone paradisi), Chestnut-bellied Malkoha (Phaenicophaeus sumatranus) and White-bellied Sea Eagle (Haliaeetus lecuogaster) were all spotted along the walk too.

Finally, after a long hike, we arrived at the Treetop Walk, where participants were treated to beautiful views of the forest canopy and the nearby reservoir. But they were also in for a special show, as two male Common Gliding Lizards (Draco sumatranus) vied for control of a tree trunk just next to the suspension bridge! Flashing their bright yellow dewlaps and chasing each other round the branches, they made for an arresting sight. Draco is Latin for dragon, and the aptly named Dragons were soon taking to the air, gliding between branches as they sought to assert their dominance without actually coming to blows.  They even performed boomerang manouevres that allowed them to quickly leap to spots lower down on the trunk!

The fun didn’t end at the Treetop Walk though; we continued to spot many herps along the way back! One of them was the Clouded Monitor (Varanus nebulosus), which unlike its bigger relative is largely restricted to forested areas. As the sun continued to rise, many of them were out and about, and we spotted several before the day was done.

Saving the best for last, we were very fortunate to spot the Yellow Striped Tree Skink (Lipinia vittigera) back at the Ranger Station! This tiny lizard is rarely seen in Singapore, making it a very special find indeed! It soon captivated everyone’s attention, and the sort of paparazzi normally reserved for rare birds soon surrounded the tree that it was perched on. It was very heartening to see a tiny herptile get so much attention, and after a brief phototaking session, we left it to its own devices in peace.

Animals such as the Yellow Striped Tree Skink are part of what makes the Central Catchment Forest worth preserving for future generations. Before we finished our walk, we educated participants about the proposed Cross Island Line, which could pass through the very rainforest that they had just walked through. We encouraged them to bring their friends to visit the forest and spread awareness of the consequences of building an MRT line through our nature reserves. Hopefully, we can protect the flora and fauna for future generations to enjoy.

We hope everyone enjoyed themselves, and despite what this signboard says, learned that snakes and other herptiles are not be feared, but to be loved!

Check out more photos from some of our participants!
[1] – Hock Chuan Ang shares some of his photos from the Herp Walk here