Invasive Species

Battling the brown tree snake in Guam

In the dense tropical forest, a slither of movement can just be made out in the glow of our head torches.

A snake is entwined in the undergrowth. It is about 1m long, mostly dull brown but with a vivid yellow underbelly.

We are face to face with Guam’s “nemesis”: the brown tree snake. And the forests here are dripping with them.

The US territory, in the western Pacific, is only 50km (30 miles) long and 10km wide, but it is packed with two million snakes.

This reptile arrived here only 60 years ago but has rapidly become one of the most successful invasive species ever.

Unhealthy appetite

Wildlife biologist James Stanford, from the US Geological Survey, says: “Our belief is that they came at the end of World War II.

“We’ve looked at their genetics and they are all extremely closely related, and it appears they came from the Island of Manus in Papua New Guinea.”

He explains that military equipment used by the US in Papua New Guinea while the war raged in the Pacific was eventually sent back to Guam to be processed. A snake probably crept on to a ship or a plane destined for the island.

“And from that handful, or maybe even one already impregnated female, we now have a population that is unbelievable in scale,” he says.

The snakes, which are mildly venomous, have caused many problems. They get everywhere, and people have even woken up with them in their beds.

The island’s power system is regularly shorted out by snakes crawling on the lines. It is so frequent the locals now call power cuts “brown outs”.

But the biggest impact has been on the wildlife – it has been decimated. The forests here are eerily quiet. Now the only place where the Guam’s native birds, such as the koko, can be seen on the island are in cages in a captive breeding centre.

“The brown tree snake has had a devastating impact. Ten out of 12 native forest bird species disappeared in 30 years,” says Cheryl Calaustro from Guam’s Department of Agriculture.

“The birds here evolved without predators. They were quite naive. And when the snake arrived on Guam it ate eggs, juveniles, adults. Whole generations disappeared.”

Source: BBC News Read more

Comment:

Another example, although inadvertant in this case, of how man’s carelessness damages the natural balance.