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  Of Aliens that follow in Man's footsteps ...
and the harm that they can do!

Main article | The 'Aliens' in Singapore | No Winners in War against 'Aliens'

Modern man is a great traveller .. but little does he realise as he globe-trots that his baggage comprises not only his worldly possessions but hitching a ride are innumerable 'aliens'! No, this is not some sci-fi scenario. This is a common everyday occurrence and it's not something new either. It's been happening for eons as man migrates and his domesticated animals and plants travel with him. Lim Kim Seng reports.

Man has been constantly migrating and, as he moves, he brings with him plants and animals familiar to him. His cattle, horses, pigs, dogs, cats move along with him, so do 'living' grains like rice, wheat, maize (corn) and root crops like cassava. These plant foods give him sustenance while his animals also offer companionship.

And as man roves far and wide he introduces animals and plants into places where they do not belong. And it is not just the animals and the plants that he knowingly brings with him that are introduced but, unknown to him, his animals and his food harbour all kinds of insects and even animals, like rats!

Even grass seeds, trapped in his clothes and his hair, are introduced, along with the mites and other micro-organisms on his skin. (And don't think that our skins today—scrubbed with soaps and drenched with deodorants—do not harbour micro-organisms, they do).

Then, as time went on, these introductions thrived and grew vigorous, so vigorous that nowadays scientists warn that the introduction of exotic, animals and plants into places where they do not belong ranks, alongside habitat loss and hunting, as one of the major concerns of nature conservationists.

Rampant introductions everywhere in the world has resulted in indigenous species being exterminated or becoming much reduced in numbers, to the extent that they have become endangered, again in virtually every corner of the world. Introductions may be deliberate or accidental: whatever the case, their effect on native wildlife can be devastating!


Natural historians say that the seafaring Polynesians and the European caused the most damage in centuries past (but it probably took them hundreds of years to do what we, 20th century man, have done in just 50 years of accelerated globalization). Polynesians' impact
They arrived about AD 500 in NZ together with rats (Polynesian) and dogs. These animals preyed on the eggs of the moas and other animals. The Polynesians' greatest impact was on the moas which they managed to wipe out through direct persecution for food and forest clearance. Over a period of a thousand years, all 20 species or so of moas were wiped out.
Settlers caused great damage when they cleared forest to create homes and build a community (but nothing like the supermarket/shopping/entertainment mega-centres of today!) Still, such activities coupled with direct hunting and also their introduction of domestic animals and crops collectively added up.

For example, well before European settlers (mostly English) landed in New Zealand in the wake of Captain Cook's discovery of the Eden-like 'Land of the Long White Cloud', the Maoris had, through forest clearance and hunting for food, caused the extinction of up to 20 species of flightless birds, the moas. (And this had occurred by the 17th century). So, by the time Captain Cook 'discovered' New Zealand, the moas were no more.

Worse was to come. The European settlers brought with them dogs, cats and the inevitable rat, all of which preyed on the ground-dwelling animals there. They also brought in deer and cattle and these reduced foraging areas for native animals. Also introduced were fast-breeding rabbits, stoats and pigs. Then the homesick settlers caused more mayhem by introducing European birds such as House Sparrow, Rock Pigeon, European Starling, Dunnock, Greenfinch, Goldfinch as well as Black Swan, the last from Australia. In all, over 130 species of birds were introduced and of these, some 30 species are now firmly established in present-day New Zealand.

These birds often have no natural predators and compete directly with the native birds, often driving the latter out because they (the introduced species) are more aggressive. But threats to their survival also come from the introduced animals. For instance, the Kakapo, a flightless parrot and the Takahe, a flightless giant swamphen, are both threatened with extinction by introduced cats, rats and stoats.

Today's 'introductions' find even speedier modes of transportation to hitch a ride on. We are talking here about aircraft and some of the introductions by this mode have been almost bizarre. Take this incident which happened in the South Pacific island of Guam in the 1970s Biologists became alarmed that birds had started disappearing from the forests there. By the 1980s, the forests of Guam had fallen eerily silent. Incredibly, virtually every bird seemed to have disappeared.

The endemic Guam Flycatcher became extinct. Gone too were the Bridled White-eye, Rufous Fantail, White-throated Ground-dove, Mariana Fruit-dove and Micronesian Honeyeater. Fortunately, as the flightless Guam Rail and Micronesian dwindled to a scattered few, Guam biologists came to the rescue, evacuating them to zoos for 'safekeeping' and captive breeding. (A necessary measure but not an entirely good thing to have to do to wild animals).

Interestingly, at first nobody knew what had caused the loss of Guam's native forest birds. Pesticide poisoning, habitat loss and the avian pox all came under suspicion.
Finally, after years of painstaking investigation, the culprit was found to be an introduced animal—the Brown Treesnake of New Guinea which had been brought into Guam on one of the cargo planes that ply the Pacific islands.
Brown Treesnake were suspected to have been first brought in as early as WWII on board American bombers plying the Pacific. These were increased by continued trade between these islands after WWII.
Somehow the Brown Treesnakes population had exploded—probably due to its having no natural predators and abundant prey. And, as these Treesnakes got out of control they wiped out the resident species one by one, even native snakes, skinks and geckoes fell prey to them. Today this menace is still around, having eluded efforts to eliminate it by systematic trapping. Therefore it will be a long time more before it is safe to reintroduce the Guam Rail and Micronesian Kingfisher back to Guam. (And if it takes decades to get rid of the Treesnake, conditions in Guam's nature areas may have changed so considerably that it may not be feasible or even wise to reintroduce these species.)

In another area of the South Pacific—this time Hawaii—many birds have also sadly become extinct due to reckless deforestation and introductions. Humans, goats, deer, pigs, cattle, sheep and rats all collectively contributed to the decimation of the bird population on the Hawaiian islands. But the final blow to birds like the Black Mamo, Laysan Honeycreeper, Lesser and Greater Koa-finch, Oahu Ou, Kona Grosbeak and Hawaiian Rail was dealt by an introduction as small as a mosquito—the deadly Culex mosquito which in the 1820s provided a vehicle for infecting birds with avian malaria. Fortunately highland birds were safe because the Culex mosquito could not penetrate above 2,000 feet.

This article is part 2 of a 2-part feature on Introductions and Re-introductions. The second part, entitled 'Playing Modern-Day Noah: Tempting but Highly Dangerous' was published in Nature Watch Vol 7 No. 1 Jan-Apr 1999.

The writer Lim Kim Seng is a member of the NSS Conservation Sub-committee. He was the co-ordinator of a four-year bird survey of the nature reserves which was organised by the National Parks Board and conducted with the help of NSS volunteers. The survey was concluded in 1997.

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