Site map | NSS Home Page
Official Magazine of the Nature Society (Singapore)
  The 'Aliens' in Singapore
Main article | The 'Aliens' in Singapore | No Winners in War against 'Aliens'

by Lim Kim Seng

Member, Conservation Sub-committee
Nature Society (Singapore)


The first alien arrivals to Singapore's shores were probably small in numbers and slow, spread over a long, long time. But after Stamford Raffles 'founded' Singapore in 1819, man, animals and plants arrived in great numbers.

As this British trading outpost at the cross roads of Southeast Asia flourished, travellers from all over the globe came in search of fortune. Fortune for some came in the form of harvests from commercial crops like gambier, pepper, pineapple, tobacco and rubber—all alien invaders supplanting native forest trees.

As the settlement grew, more aliens were introduced, this time they were wildflowers such as the so-called Singapore Rhododendron, Clidemia and Peperomia, all of which were brought from such faraway places like South America. (Rubber was introduced from Brazil).

Even large shade trees were introduced and these included the South American Rain Tree and the currently common roadside African Mahogany. The Water Hyacinth was introduced (probably by Chinese migrants to feed their ducks and pigs) and their unchecked proliferation have choked waterways (most likely because there are no more pigs in our rural areas or fish in our polluted waterways).

Some of these alien introductions were deliberate, others accidental but whatever the case, most introduced plants are now part of our Singapore landscape and especially evident in urban areas. In Singapore, as has been the experience elsewhere, the aliens, both plants and animals,, are vigorous and can supplant the natives.

Do you know that more than 11% (19 species) of our resident birds were originally aliens? They've had permanent residence for so long they can be deemed to have become naturalised! These include the Rock Pigeon, House Crow, Javan Myna and Eurasian Treesparrow. All these birds are among the top 20 in the Bird Census held every year.

What this shows is that introduced birds can cause problems by competing with native birds for food—especially in diminishing nature areas.

And alien bird arrivals are growing every year. Since 1986 the Nature Society's Bird Group has recorded more than 100 alien species in the wild and these include seven hornbill species, several cockatoos, Budgerigar, Mute and Black Swans, Painted and Milky Storks, Common Peafowl, Green Wood-hoopoe, Rockhopper Penguin and Japanese White-eye.

Who's to blame for this continuous invasion?

The active cage bird trade is largely to blame. But the ranks of aliens have also been swelled by free-flying birds from the Bird Park and the zoo; also from private collections and even by birds and animals (mostly tortoises) bought and released emass on religious occasions such as Vesak Day (The Buddha's birthday). While one can appreciate the sentiments behind wanting to set free a poor caged animal, such releases can actually do more harm to both the freed birds and also the resident avifauna. This is because, once released, some of the birds die because they cannot find food in the strange new environment they suddenly find themselves in. Or they are quickly eaten by predators.

Those that do survive—by finding themselves some vacant niche—may go on to compete for food with native species. They may even become abundant enough to cause more problems.

A good example is the House Crow. The House Crow was introduced during World War II to combat a plague of caterpillars. It is not known whether they managed to contain the plague but what is known is that this common bird has itself become a nuisance. The House Crow spread steadily and in 1985 it had successfully colonised the whole of Singapore, including Pulau Ubin. A few crows may carry contagious diseases like avian pox and infect other resident birds.

From left to right
Red-eared Terrapin (North America)
Hairy Clidemia (South America)
American Cockroach (North America)
Norway Rat (Europe)
Javan Myna (Indonesia)
Eurasian Tree Sparrow (North Asia)
Mile-a-minute (South America)


Mammal 'aliens' are small but can be abundant
Most of the mammals introduced into Singapore have been small rodent—and these include the House Mouse, House Shrew, House Rat, Norway Rat and Burmese Rat. These lurk in drains, sewers, ports and warehouses and can be abundant. Some of these rodents carry dangerous diseases such as scrub typhus which can infect humans. The Zoo has contributed to this problem in its own way. Many mammals have escaped (and continue to do so, from time to time) and these include Tiger, Leopard, Hippopotamus and Sambar. Some, like the Sambar, still persist outside the Zoo and since the Zoo is located within the nature reserves where many of our threatened native animals and plants are just 'hanging on', there is potentially a great threat which needs to be addressed.

Even in the amphibian and reptile sectors, introductions are posing threats to native survival. Most notable of these is the Changeable Lizard of Thailand, a close cousin of the native Green Crested Lizard which is a forest species. The Changeable Lizard was introduced in the 1980s, probably in one of the fruit shipments from Thailand. Since then this lizard has been found throughout the island and recently it was spotted in Johor Bahru. As a result of the Changeable Lizard's arrival and spread, our native Green Crested Lizard has retreated from its former rural habitat and is now found mainly in our forests. So far the Changeable Lizard has not invaded its cousin's space in the forest.

Of more concern is the American Bullfrog which is brought in to satisfy the palates of frog-legs gourmets. Some of these bullfrogs have eluded the cooking pot, thanks to the timely intervention of those compassionate souls who bought their release. But after being freed and having found their way into our nature reserves, these hefty bullfrogs are posing a grave threat to our native amphibians. (Perhaps it's like American basketballers coming into the Singapore basketballers' court).

Then in our lakes and waterways we also find evidence of alien introductions such as the versatile South American Guppy, found in drains and canals. There's also the North American Red-eared Slider, a terrapin, and the African Tilapia (fish).

But introductions are also found right at home. The much loathed cockcroaches are mainly American or German cockroaches—their names reveal their origin. In our rice jars we often find the rice weevil and if we don't clear our food fast enough, armies of tiny Pharoah's Ants will be swarming over it. Other examples include the housefly, fleas, bedbugs and silverfish.

From left to right
Guppy (South America)
Water Hyacinth (South America)
American Bullfrog (North America)
Singapore Rhododendron (South America)
Changeable Lizard (Thailand)

Aliens can cause severe ecological problems
Introducing alien species have caused severe ecological problems everywhere. They pose problems by directly competing with native species and also by their bringing with them unknown diseases. There is therefore an urgent need for the government here to enforce stricter controls on the import of livestock, but it's not easy to strike a balance between lax controls and overzealous ones. (The 'cure' for introduction problems can be worse than the problem.)

There is also a need to educate the public and the zoo that the indiscriminate release of animals into the wild can cause a lot of harm and do no good even for the animals released. Ultimately the war against introductions is a grim one, and usually a vain one, because despite strict government controls and public awareness, there will still be some alien animal or plant species that slip through. Sometimes the only thing that we can do about introductions is to monitor and wait and see.

<<Back to Issue contents

 
© Nature Society Singapore