EDINBURGH, Scotland, June 7 (UPI) -- Clearing a small island in the Scottish Hebrides of rats took three years and cost 50 pounds ($100) per rat.
Officials waited two years after the last rat was sighted on Canna before declaring it rat-free, The Scotsman reported. One sign that they are all gone is the first Manx shearwater chick to hatch in a decade.
Canna, just slightly more than 4 miles long and 1 mile wide, belongs to the National Trust for Scotland, which arranged the extermination.
In 2005, there were believed to be 10,000 rats on Canna, the descendants of a few that had arrived by boat decades before. They devoured the eggs and chicks of nesting seabirds, and the 1,500 Manx shearwater on the island had been reduced to two.
Wildlife Management International, a New Zealand company, was hired to get rid of the rats. The company set out poisoned bait traps, using plastic tubes to protect larger mammals.
The project cost 500,000 pounds ($1 million).
One concern was the Canna mouse, a rodent unique to the island. The trust moved 158 mice into zoos to ensure some would survive, but it turned out that most escaped the rat traps.