Environmental Engineering Reference
In-Depth Information
The snakes' notoriety grew. They got a reputation for entering houses and taking nips at babies
in their cots. There were more than a hundred cases requiring hospitalization.
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The invaders climbed
wooden poles carrying power lines, presumably mistaking them for trees, and slithered along the wires
looking for snoozing birds. Growing up to ten feet long, they were heavy enough to sometimes drag
down the lines, causing hundreds of power outages.
There are many theories as to why this previously little-noticed snake caused such a stir on Guam.
It certainly stumbled on a place where snakes were a novelty. Local victims had no idea how to defend
against the newcomers. But, equally, it may have found an island ecosystem in crisis and wide open to
takeover. Guam had only fragments of its old forests. Most had long been cleared for coconut planta-
tions. Much of the island had been bombed by the United States and Japan as they fought during the
Second World War. It had then been washed with DDT to rid it of malaria. By the time the carpetbagger
snake showed up, the remains of the native forests were rapidly being cleared for the runways, houses,
golf courses, and other infrastructure needed to satisfy tens of thousands of US troops on an island less
than a sixth the size of Long Island.
Such changes—by disrupting existing ecosystems, removing other species, and creating numerous
ways for the incomers to prosper—must surely have contributed to both the wildlife decline and the con-
ditions that allowed the remarkable spread of this hungry and crafty snake. The snake cannot be blamed
for the loss of several species of birds that had all but gone before it showed up. The nearby US-run
island of Rota, which was at the time free of snakes, has shown a similar decline in native forest birds,
which ornithologists attributed to habitat loss.
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Without the snake, there would undoubtedly be many
more birds on Guam today; but without the massive disruption caused by the arrival of the US military
in particular, the snake is unlikely to have prospered so well.
The heyday of the brown tree snake on Guam may be past, however. Its numbers have fallen to
roughly half the four million estimated during its marauding 1980s peak. Perhaps it has simply been too
successful in eating the available food. But the US military is taking no chances. In the spring of 2013,
it dropped thousands of dead mice into the forests of Guam. Each mouse carcass was stuffed with tab-
lets containing paracetamol and kitted out with a tiny parachute made of green tissue paper. The mice
floated into the branches, where the plan was for them to be gobbled up by the snakes, for whom the
Stories from places like Guam and Gough Island have created a widespread assumption that oceanic
islands are sitting ducks for disaster once alien species arrive. Many also conclude that islands reveal
the worldwide effect of aliens in a microcosm. Neither is true. Isolated islands have very singular eco-
systems, and there is no reason to think the rest of the world will be like them. When Christoph Kueffer,
an ecologist at the Swiss Federal Institute of Technology in Zurich, looked at over 250 “invader” plants
on thirty island groups from Ascension to the Virgin Islands, he found that only a handful of the in-
vaders—out of tens of thousands of known introductions—were of much consequence for local species.
Most alien species add to local diversity and enrich species-poor ecosystems. There are many more is-
lands like Ascension and Hawaii than like Gough or Guam.
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