On an isolated archipelago off the B.C. coast renowned for its luscious rainforests, rugged coastlines and rich Haida culture, a full-scale assault is about to be unleashed on the lowly rat. The aim: eradication.
Norway and black rats have been decimating seabird and songbird populations in Gwaii Haanas National Park Reserve, stealing and feasting on their eggs and chicks. Ancient murrelets are in particular danger. A black-and-white seabird about the size of a pigeon, the murrelet is on Canada's species-at-risk watch list.
But the tables will turn this summer. After documenting the rats' destruction via sensor-equipped digital cameras, Parks Canada will in August lay poisonous bait for the rodents on Arichika and Bischof islands. If all goes according to plan, every last rat will be killed and the eradication effort will expand to at least two other islands in the national park.
In all, rats have been detected on 18 islands in Haida Gwaii, formerly known as the Queen Charlotte Islands. They were introduced to the archipelago in the late 1700s, stowaways on ships.
The rodents and other invasive species are among the most significant threats to the park's ecological integrity, said Laurie Wein, acting resource conservation manager at Gwaii Haanas. Simply reducing the rat population isn't enough.
"Rats are such prolific breeders that that's just not a feasible option," Ms. Wein said. "Their population would rebound in three to four months."
Rat removal is a major logistical challenge, but one that has been accomplished before in Canada and elsewhere. Parks Canada, which manages Gwaii Haanas with the Haida Nation, has enlisted the help of Island Conservation, a non-profit group known internationally as adept killers of rats and other invasive species.
The California-based organization has worked on 45 islands, from Alaska to the Caribbean and South America, saving 288 animals and plants from the threat of extinction in the past 17 years. Its most recent high-profile mission was in Ecuador's Galapagos Islands, where rats were threatening the survival of birds, tortoises, iguanas and native plants.
"Rats are one of the worst species on the planet. They're responsible for about half of all bird and reptile extinctions on islands around the world," said Gregg Howald, Island Conservation's North America regional director.
Whenever rodents are targeted, other animals could also be poisoned, as was the case when the Canadian Wildlife Service took aim at Norway rats on Haida Gwaii's Langara Island in 1995.
Several ravens broke into the poisonous bait stations, while others died after consuming dead rats. Bald eagles were also affected. A 1997 study by Mr. Howald showed about 15 per cent of Langara's bald eagle population was inadvertently exposed to rodenticide, likely as a result of eating ravens. However, none of the eagles died.
Bait stations have evolved significantly, Mr. Howald said, limiting the risk to other animals. The devices are locked and secured more firmly to the ground. They're also designed to make it impossible for other animals to reach in and snatch the poisonous bait.
In the Arichika and Bischof islands of Gwaii Haanas park, about 420 black-plastic bait stations will be placed in a grid pattern, about 50 metres apart. They resemble shoe boxes with holes cut into each end. Inside, corridors will lead rats to a poisonous block of bait.
Staff from Parks Canada and Island Conservation will check the islands for carcasses daily for about eight weeks. Most of the rodents are expected to die underground in their burrows.
The bait stations will be kept on the islands for two years, after which Arichika and Bischof will be declared rat-free if no more are found. These islands were chosen as the starting ground for the $1.6-million eradication project in part because of their safe distance from the park's other rat-occupied islands, Ms. Wein said. Norway rats can swim up to a kilometre.
Parks Canada has an education campaign geared toward preventing visitors from unintentionally introducing more rats to the archipelago. When the rats are gone from Arichika and Bischof, officials hope the population of ancient murrelet and another seabird, Cassin's auklet, will recover. Parks Canada plans to attract breeding pairs from neighbouring islands to help recolonize the birds.
Surveys in the 1970s detected 1,600 pairs of murrelets and 700 pairs of auklets. By the mid-1980s, their numbers had declined to 20 pairs and 50 pairs, respectively.
"Today, we are not finding any birds at all," Ms. Wein said.
But rats aren't the only non-native species wreaking havoc on the ecosystem of Haida Gwaii. Raccoons are also plaguing seabirds, and large populations of Sitka mule deer are disrupting island forests.
Reports of invasive animals, plants and micro-organisms are on the rise across Canada, a consequence of increased global trade and travel. They tend to dominate the landscapes they invade, muscling out native species and altering the natural balance.
With invasive species at unprecedented levels in Canada, a University of Waterloo researcher suggests more careful analysis is needed of which invaders to combat and which to leave be.
"We can't be controlling every one of these species because global trade continues to spread them around," said assistant environment studies professor Brendon Larson, whose research includes biodiversity science.
For Parks Canada and the Haida Nation, rats are one invasive species worth tackling. Mr. Howald noted seabird recovery can be swift and dramatic after rat eradication. On Anacapa Island off the California coast, for instance, Mr. Howald said it took only months for seabirds to begin using the island, breeding successfully for the first time in a long while.