Eco-Link@BKE: Safe passage for creatures over busy highway
Friday, 11 December 2015
Can animals find the link?
There are no signs, and no, the animals don’t read maps. But somehow, they have found their way to a 50m-wide bridge in the centre of a 2,000ha reserve.
"A lot of people were very sceptical - there is a whole long stretch of BKE, will the animals be able to find it?" said Ms Sharon Chan, who oversees the team managing the eco-link project.
Ms Chan, deputy director at NParks, said the team was extremely excited when camera traps captured footage of pangolins and palm civets using the link to cross between the Bukit Timah and Central Catchment nature reserves in October 2014.
Take the common palm civet, also called the musang or toddy cat, which is known for its odorous scent and taste for palm sap. More than one has been captured on cameras crossing the link every month, Ms Chan said.
It is not classified as endangered, but still a rare sight here.
"I was based in Bukit Timah (Nature Reserve) in the 1990s, and I would only get a whiff of it... I had a hard time looking for them," she told The Straits Times.
The solitary animals are territorial. When food gets scarce, they are less able to co-exist in close quarters.
Previously, when they tried to move out of the nature reserve, “it’s road road road road road, noise noise noise noise noise – they have a hard time finding their way out", Ms Chan said.
Having the civets cross from reserve to reserve is also good for the plants, as they excrete the seeds from the fruit they eat, and help to disperse them - enhancing plant biodiversity.
It’s not just the land mammals, but quite a few varieties of birds who needed help. Species like the emerald dove and the striped tit-babbler do not fly long distances, and prefer to hop from shrub to shrub.
Besides food, the birds also seek cover to hide from predators. The emerald dove, for instance, tends to hide away in the undergrowth at the slightest sign of danger.
It has been spotted using the link as the vegetation matured into medium-sized shrubs and small trees.
Using bat detectors capable of picking up the ultrasonic bat calls, one study has found that bats are also regular users of the eco-link.
At least one species, the glossy horseshoe bat, would not be able to cross the link without help.
The tiny bat, just 4g to 8g in weight, is adapted to fly through undergrowth that protects it from the elements.
"Because of the vegetation – it’s more complex, there are more insects, which draws in the bats," said researcher Benjamin Lee, a PhD student at the Durrell Institute of Conservation and Ecology at the University of Kent.
So while no one knows how exactly the animals find the link, it seems that some combination of factors in the design of the bridge draw them to it and off the roads.
The problem with designing a bridge for animals is that you can’t ask them what they would like. But through observing the animals, and their understanding of the local ecology, the team at NParks set out to build one that the wildlife here would use.
Wildlife crossings are now common in Europe, Canada and the US, but the Eco-Link@BKE is the first purpose-built bridge for wildlife in South-east Asia, and possibly Asia.
Before work started, the team at NParks went to Switzerland and the Netherlands, which have built hundreds of wildlife crossings.
From that study trip, they determined that the minimum width of the bridge should be 50m for the animals to “feel comfortable” on it. The hour-glass shape was also designed to encourage wildlife crossings.
But the European crossings were built for a temperate climate.
Singapore’s eco-link had to be adapted to an equatorial climate, tropical foliage and the very different animals that evolved in this environment.
Said Mr Wong Tuan Wah, NParks’ director of conservation: "We are a tropical country... so the vegetation there is very different... but the principles are the same worldwide - to reconnect two halves of a forested area."
After plans for the eco-link were announced in 2009, NParks embarked on surveys of the area, and put in camera traps before construction started to monitor the animals already in the area.
Said Ms Chan of NParks: “During construction, we also did a quick check to make sure it did not affect the animals. If not, we would end up with a bridge where no animals are there.”
In July 2011, construction of the link by Eng Lee Engineering began. The soil on the eco-link originates from the site - it was excavated and stored when construction began.
The depth of the soil on the link was also made deeper, to improve water retention, and ensure that tall trees can take root.
After the eco-link was completed in 2013, native trees and shrubs were planted along the bridge to mimic the rainforest.
Plants along the edges of the link act as a buffer to screen noise and lights from the expressway below.
In the centre of the link, trees that can grow to 15m were planted. When mature, they will create a dense canopy that simulates a natural forest environment. The plants were also chosen to provide food for the animals, and draw them in.
When reporters visited the link on Nov 4, 2015, traffic bustled on each side of the link and helicopters whopped overhead, but within the heart of the eco-link, it was no man’s land.
Listen to the constant hum of sound that can be heard from the bridge. Despite the noise, animals haven't been deterred from using the eco-link.
No paths, no lights and most of the time, no humans allowed. On both ends of the link, “No Entry” signs are a warning to homo sapiens who may think to trespass.
The guided walks for the public are limited to a gravel path on the side of the link.
Dr Shawn Lum, president of the Nature Society (Singapore), said that there had been initial concerns about whether animals would really use the bridge, given the traffic noise and the exposed environment, but these did not come about.
"Wildlife is starting to come and the vegetation is starting to grow... So I’m delighted, and whatever initial concerns or worries that we had, luckily turned out not to have materialised," he said.
But like humans, there are some animals NParks wants to keep out of Bukit Timah Nature Reserve, specifically wild boar and Sambar deer.
At one end of the eco-link lies a fence, with only a 30cm gap at the bottom, for smaller mammals like pangolins, squirrels and civets.
That is because boars and deer can damage the forest environment, and the smaller Bukit Timah Nature Reserve is not able to sustain the large mammals. Boars, in particular, like to dig the ground for worms, unearthing saplings and disrupting the forest floor.
The other reason they are kept out is to minimise chance encounters with humans.
Urbanised Singaporeans sometimes "freak out" when they come face to face with a wild animal, Ms Chan said.
"If they don’t know the animal, they don’t understand the animal and they will fear the animal, so that is why the outreach programme is very important," she said. "The guided walk is to tell people what we are doing, and about the animals. We want to remove the doubt, so they can help us protect them."
Bringing back the banded leaf monkey and flying lemur
One of the animals Singaporeans have had little chance to know is the banded leaf monkey, one of two types of monkeys native to Singapore. They are elusive, prefer to stay high up in the tree canopy, and, with an estimated 40 to 60 monkeys remaining in Singapore, rare.
Their more vivacious cousins, the long-tailed macaques, are more commonly sighted, and have been seen using the eco-link to cross the BKE. But they are so acclimatised to humans that they also use pedestrian overhead bridges to cross roads.
With the eco-link in place, Ms Chan of NParks hopes that the banded leaf monkey will one day make its way to Bukit Timah.
She also looks forward to spotting the Malayan colugo (flying lemur) and the red-cheeked flying squirrel on the eco-link when the trees grow tall enough to support them.
“These are all the future animals that we want to play matchmaker to. Otherwise some will only be on one side, and they can only look at one another,” Ms Chan quipped.
Besides the banded leaf monkey and Malayan colugo, another pool of animals that may need more help to cross the link are frogs.
As it is now, the eco-link is a little on the dry side for amphibians.
“They are reliant on streams, pools and moist areas. To abandon that and cross the eco-link is difficult for them,” said wildlife consultant Subaraj, who added that the link is still “a step in the right direction”.
For the frogs to hop on, areas with “ephemeral ponds or seeps” are needed, said Dr Lum of the Nature Society (Singapore).
But he too sees hope for the future.
He said: "Even if only a few species were to recolonise, stabilise, or increase in number in the Bukit Timah Nature Reserve, I would consider the eco-link a great success, as this would suggest that degradation of wildlife in an isolated Bukit Timah may have been arrested."
In fact, efforts to improve the link are ongoing. NParks is continually monitoring the area using camera traps, and data is collected and analysed regularly. Research studies are also being planned, or are in progress.
The banded leaf monkey’s range has been largely limited to the Nee Soon Swamp area in the Central Catchment Nature Reserve since 1987, when the last survivor in Bukit Timah met an untimely death.
The disappearance of the banded leaf monkey from Bukit Timah is a tale that has gained “folkloric proportions” in the nature community, said Dr Lum of the Nature Society (Singapore).
It is said that the lone elderly female primate came to the ground, and was mauled to death by a dog (some say a pack of dogs) from a nearby village.
Once common, the monkey has been rare in Singapore since the 1930s, and only one troop was left in Bukit Timah by the 1960s.
While the population in Bukit Timah reserve had been in decline before the BKE was built, the construction of the highway ensured that animals lost from the forest would likely not be able to re-colonise it, Dr Lum said.
In recent years, there has been anecdotal evidence that the monkeys are venturing out of Nee Soon Swamp. But they have yet to be seen in MacRitchie Reservoir where the link is located, said Ms Andie Ang, who studied the monkeys from 2008 to 2010 for her master's thesis. She is now a doctoral student at the University of Colorado Boulder in the United States.
As things stand, it may be a few more years before the link can be used by the banded leaf monkey. Being an arboreal species, they thrive in the tree tops, and rarely come to the ground.
The trees in the eco-link will need to grow much taller to form an “overpass” for the monkeys.
Having two populations of monkeys, in the Central Catchment area and in Bukit Timah, will be better than having one, said Dr Amrita Srivathsan, a biologist at the National University of Singapore. “Their chances of survival will increase,” said Dr Amrita, who has conducted genetic research on the monkeys.
But it will not restore the genetic pool of the troop of monkeys that went extinct in Bukit Timah. A study done by Ms Ang and Dr Amrita found that the remaining monkeys have very low genetic variability - a long-term concern that is difficult to address.
Said Ms Ang: “If they use the eco-link, there are potentially more food sources for the monkeys, but you need more monkeys to expand the gene pool.”
The Malayan colugo or flying lemur glides from tree to tree, and hardly ever sets foot on the ground.
The trees must reach a certain height, possibly 15m, before colugos can launch off them, Ms Chan said. Even when resting, the colugos perch on tree trunks, or hang upside down on branches.
Dr Norman Lim, who has published a book on the Malayan colugo, said: “They are gliders, they don’t come down to the ground, so there must be enough connecting routes for them to get from one place to another.”
While he has seen colugos gliding over roads like the Mandai Lake Road, they prefer dense canopy.
There are about 1,000 colugos in the wild here, which makes their situation less precarious than the banded leaf monkey’s. And unlike the monkeys, the link may help to enhance their genetic pool.
Said Dr Lim, a lecturer at the National Institute of Education: "With the habitats connected, two populations of colugos which were previously separated have the chance to interbreed."
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Source: The Straits Times (Online), © Singapore Press Holdings Ltd. Permission is required for full and/or partial reproduction.