Rat evades men, dogs and traps!

One of the most important steps in conservation of islands is to get rid of alien species particularly predators like rats. Rat eradication has been successful on several islands in Seychelles including Darros, Denis and Fregate. The eradication programmes on these private islands were conducted in collaboration with the Seychelles government and Nature Seychelles and we know that the biggest headache after eradication is to prevent rats from re-invading. In fact at least three islands in Seychelles were re-invaded after eradication.

In New Zealand, conservation scientists have recently attempted something novel. They have introduced a rat on an island that was rat free. Scientists wanted to study rat “re-invasion behavior”. Sounds like a war? Well it is. A battle between men and rodents with the fate of endangered wildlife in the balance. Scientists say that because of the horrendously difficult and costly exercise of restoring islands, it is important to know how far rats move when they arrive on an island, and how quickly the population increases.

A single Norway rat, fitted with a radio transmitter was released on the 24-acre island of Motuhoropapa. The idea was to track the rat’s movements and behavior. Well, the plans of rats and men do not usually come together! The rat proved smarter than the scientific team and avoided traps, baits and hunting dogs. After two and half months on the island the rat decided to abandon the experiment. It swam to another rat-free island, a distance of 400 meters, where it ended up in a trap baited with penguin blubber some weeks later. This is the longest distance recorded for a rat across open sea.

Writing in the journal Nature, the scientists said the results show that eliminating a single invading rat is very difficult. Invading rats on remote islands off the coast of New Zealand are a recurring problem. Norway rats have invaded Noises Islands at least six times between 1981 and 2002.
New Zealand is a world leader in eradicating rats. In fact, experts from that country have been involved in all the successful eradication programmes in Seychelles. The largest ever rat eradication was conducted not too long ago on New Zealand’s Campbell Island at a cost of 2 million Dollars. In Seychelles, the costs can range from about 22,000 Dollars on a coral island like Denis to almost 60,000 dollars on a granitic island such as Fregate.

The study by the New Zealanders confirms that re-invasion can happen quickly and rats can remain unseen until it is too late and the population has grown to a point where another large-scale (and perhaps costlier) eradication has to be attempted. There are lessons for us to learn from this experiment.

By Nirmal Shah, Nature Seychelles' CEO, published on The People Newspaper, Seychelles

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