The Haida Gwaii archipelago, of which 16 islands are rat-infested, are no exception. Together the Haida Gwaii islands host more unique subspecies than any equivalent area in Canada, including the morphologically unique Haida Gwaii black bear, the Queen Charlotte goshawk, northern saw-whet owl and Queen Charlotte ermine as well as unique forms of the Stellar's jay and hairy woodpecker. The islands are also home to half of the world's population of ancient murrelets and one fifth of the world's breeding Cassin's auklets. To give you an idea of the devastation the rodents wreak, after the introduction of rats to Langara Island, presumably from fishing boats or log barges in 1946, the number of ancient murrelet breeding pairs plummeted from 200,000 to 20,000. In a bid to boost the bird's numbers, rats were eradicated from the island in 1995 and, sure enough, between 1999 and 2004 the murrelet breeding population is believed to have doubled.
Some of the islands have dealt with rats problems for much longer. "These rats that they're chasing are ship rats that probably go back to the 1700s when the Spanish and English started competing for sea otter pelts," says Gregg Howald, director of the North America Region for Island Conservation, a U.S. conservation group. "So this is turning back the clock hundreds of years." Invasive species, of which rats are forefront, are deemed to be the single largest threat to the ecological integrity of the Gwaii Haanas National Park Reserve by Parks Canada and the Haida First Nation, Wein says.
"Don't underestimate them, they are born survivors," says DOC's McClelland, the world's leading rat eradication expert, who was consulting on the recent trials in Gwaii Haanas. "But if you want the seabirds you can't have rats." With rats gone, the entire island ecosystem and nutrient cycle is expected to be restored because seabirds shift marine nutrients to forest ecosystems via their seafood diet and defecation.
Of course, if ingested, the rodenticide will kill other small mammals like deer mice and native shrews, but wildlife surveys show that the former is absent from these islands and that the latter exists at very low densities, likely due to being outcompeted or predated by the invasive rats anyway. In the worst-case scenario, if these mammals don't bounce back after the eradication, Parks Canada will reintroduce these species to the islands.
As for the birds, "if we see a rebound [of seabirds] within five years we'll be pretty pleased," says Wein, who has her sights set first on removing rats from Kunghit Island, a 12,704-hectare island in the southern part of Gwaii Haanas. "That's sort of the gold standard for us." The current record for the largest rat eradication is held by the Australians, who ran a successful eradication program last winter on Macquarie Island, which is 13,000 hectares.
Parks Canada's upcoming eradications mark the first time rodenticide will be aerially applied in a forested North American ecosystem. "Having that barrier broken through will open up the door to other operations more broadly within the Pacific Northwest," says Island Conservation's Howald.
"It's very addictive, rat eradications, because in so much work we do in conservation it's the same battles year after year or decade after decade," McClelland says. "You do an eradication, you see those birds come back and you really do feel like you've made a difference."