Canada Declares War on Rats

In a bid to buoy flagging seabird populations, park biologists eradicate rats from islands in British Columbia

By Anne Casselman

RAT TRAP: Canada has initiated a plan to eradicate rats from a series of islands off British Columbia in a bid to help ailing bird populations. Image: C. Gill

VANCOUVER?"I have a freezer full of dead rats," says Laurie Wein, project manager at Gwaii Haanas National Park Reserve in western Canada. It's a necessary evil, for the restoration specialist leading Parks Canada's war on rats in the biodiverse archipelago of Haida Gwaii (or the Queen Charlotte Islands). "Invasive species here on Haida Gwaii are the number-one threat to ecosystem functioning."

After nearly three centuries of rat invasion, islands in the Haida Gwaii archipelago in British Columbia?known as the Gal?pagos of the North?are being restored to their original rat-free state in a bid to save beleaguered populations of nesting seabirds, whose eggs and chicks are eaten by the introduced rodents. "For seabirds that have evolved on these island systems, they haven't developed any defenses, so they're just kind of sitting ducks, so to speak," Wein says.

Already, Wein and her team have removed rats from two islands and there are plans to eradicate them from another two next year. All together, if successful, these rat eradications would be the thin end of a wedge to make other rat-infested islands in the park, which currently total 16, rat-free.

"There is pressure for Canada to take their invasive species issues more seriously," says Wein, who will launch Canada's first aerial rat eradication next fall on Murchison and Faraday islands when helicopters rigged with pellet-spraying buckets on their underbellies will rain rodenticide onto the old-growth forest below.

Late September of this year she and her crew ran a trial study on three smaller islands to establish the minimal amount of bait needed to do the job. For the trials, the crew didn't use real rodenticide but instead used bait pellets laced with pyranine, a biomarker that causes urine and feces to glow neon green under UV light. After spreading a placebo nontoxic bait at rates of 11 to 30 kilograms per hectare, the crew trapped the rats on the island to see whether they had taken the bait. "So you're sort of looking at the personal bits and if they glow nice and green, then the rat was euthanized," says Peter McClelland, program manager of outlying islands for the Department of Conservation (DOC) in New Zealand. "We're now very confident that we know how much bait has to go out so that we can reach 100 percent of those rats," Wein says. "The next step is moving towards the full eradication in the fall of 2013."

Globally, the war on rats ramped up since New Zealand started to perfect the science of clearing their islands of the rodents in the 1970s. To date there have been 466 successful rat eradications on islands worldwide according to Database of Island Invasive Species Eradications, and the numbers are climbing fast. This is important because half of the world's endangered species exist on islands and most of those are at risk of extinction due to introduced mammals that commonly include cats, rats, foxes and raccoons. Although islands make up only 5 percent of the world's landmass, they host 20 percent of the world's unique plant and animal species. The flip side of the same coin is that to date, 80 percent of extinctions recorded have taken place on islands.

Seabird populations suffer especially. Almost half of all seabirds species have declining populations according to BirdLife International, with nearly 100 species threatened by extinction worldwide.

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