Environmental Engineering Reference
In-Depth Information
Conservation Monitoring Centre, in Cambridge, England. Though many were hunted to extinction by
humans, introduced predators have certainly taken their fill. Notoriously, ground-nesting birds with no
experience of mammalian predators are suddenly confronted with mega-mice, cats or, most frequently,
rats, according to researchers at the Zoological Society of London.
The black rat (
Rattus rattus
) has been causing trouble ever since it left India for Europe some five
thousand years ago. If nothing else, it brought Europe the fleas that carried the Black Death. The Polyne-
sian rat (
Rattus exulans
) has been similarly troublesome across the Pacific. It is now being blamed for
the mysterious crash of the once grand civilization on Easter Island in the remote southeastern Pacif-
ic, whose collection of giant stone statues of humans has long mystified explorers. The theory used to
be that the Polynesian Rapa Nui people who made the statues destroyed their society by deforesting
their island. With the trees gone, the island ecosystem collapsed, and the islanders could no longer make
the boats they needed to go fishing. The once-proud island people were reduced to a small, emaciated
rabble. It was ecocide, a warning to the world about the folly of humans' environmental sins. Jared Dia-
mond asked in an article titled “Easter's End”: “Are we about to follow their lead?”
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But now it seems that when the Rapa Nui arrived on the island a thousand years ago, they also
brought seed-eating Polynesian rats. Rather than humans destroying the forests with axes and fire, it was
the rats that delivered the coup de grace, says Terry Hunt, an anthropologist at the University of Oregon.
The rats ate the seeds of the island's palm trees, so the trees did not reproduce. Virtually every palm seed
shell dug up on the island has been gnawed by a rat, Hunt says. “It was rats, more than humans, that led
to deforestation.”
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Henderson Island is a British-run World Heritage Site in the Pacific that has been uninhabited since
the Polynesians left in the seventeenth century. Unfortunately, they left behind Polynesian rats, which
have overrun the place and are currently eating their way annually through some twenty-five thousand
seabird chicks, including endemic petrels. A $1.5 million effort by ornithologists to poison the island's
rat population in 2011 failed. Zoological explorer Mike Fay spotted one while tramping across the island
was still there, probably happily breeding. The society's Jonathan Hall told me there would be “a further
eradication attempt.”
More rarely, snakes turn small islands into horror movies. Until 1950, the only snake on Guam in
the western Pacific was the Brahminy blind snake, a small, slow-moving, worm-like reptile that mostly
lived in termite mounds. Then the US military showed up. Somewhere aboard the ships and planes mov-
ing equipment from wartime bases on the Admiralty Islands of Papua New Guinea to new US Pacific
headquarters on Guam came a contingent of brown tree snakes (
Boiga irregularis
).
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On their home islands, brown tree snakes were just one element of a diverse reptilian menagerie.
But on Guam they had an electrifying effect from the moment they slithered off into the bushes. They
proliferated quickly, colonizing half the island by the mid-1960s and most of the rest by a decade later.
In places, there were soon forty snakes per acre. Venomous, with large heads and bulging eyes, they
were very different from the blind and harmless native. They traveled everywhere, climbing trees and
invading buildings during their nocturnal hunting expeditions. They ate almost anything, from dog food
to lizards, birds, and carcasses. Ten of the island's native forest bird species, along with several species
of native bats and lizards, went locally extinct after the arrival of the brown tree snake. Brought in to
work out why, avian pathologist Julie Savidge concluded that the snakes were to blame. Gordon Rodda,
who works on invasive snakes for the US Geological Survey, says there could at one time have been as
many as four snakes for every bird.
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