Parks Canada is trying to kill every rat on two B.C. islands in an effort to save bird populations threatened by the rodents.

Park rangers have set up 400 bait stations on Bischof Island and Arichika Island, two of the 18 islands in the Gwaii Haanas National Park Reserve on Haida Gwaii.

We're looking at a complete eradication," said park conservation manager Laurie Wein. "If we miss a rat, they might be pregnant and might live to re-establish that population... We have to be exceedingly thorough."

The seabird populations are already endangered, said Wein.

"The rats are voracious feeders. They'll prey on the chicks and the eggs of many of our seabird species."

Most of the poisoned rats die in their burrows. Crews check daily to gather up the few carcasses of rats that have died above ground.

Five more weeks

The rangers also determine how much poison has been consumed and replenish the bait.

The rat battle will continue to the end of September.

Wein said it will take two years of close surveillance using remote cameras and traps to determine whether the rodents are gone for good.

While the variety of rat infesting the islands can swim up to a kilometre in warmer waters, they can't handle the cold north Pacific, so they cannot use the water to escape to other islands nearby.

Rats were successfully eradicated from St. James Island and Langara Island in a similar program in the 1990s.

With files from the CBC's Betsy Trumpener