Parks Canada staff are waging war against an army of rats on two remote northern islands in Gwaii Haanas national park, in the Haida Gwaii archipelago, with an aerial drop of poison pellets they hope will eradicate the rodents and restore ecological balance.
The aerial drop is the second phase of project Night Birds Returning, a five-year, $2.5-million plan that experts hope will eradicate the rats first introduced more than century ago by visiting ships and that now number possibly in the hundreds of thousands on Murchison and Faraday islands.
"It's a veritable buffet for them," Laurie Wein, the project manager for Parks Canada, said Tuesday.
"They consume seabird eggs, they will consume the chicks, they will consume even the adult birds and because the birds nest on the ground, they are essentially defenceless."
Once-thriving, healthy seabird colonies of worldwide significance have been decimated, she said.
One of the two islands in particular was home to the largest colony of ancient murrelet in the world at one time, with more than 200,000 breeding pairs. There are now just 14,000 breeding pairs.
The aim is to eradicate every rat, in the hope that the ancient murrelet and other species – Cassin's auklet, fork-tailed storm petrel, Leach's storm petrel, marbled murrelet, black oyster-catcher – will rebound.
"You cannot leave even a single rat behind because that rat could be pregnant, she could have offspring, and because rats are such prolific breeders, they can quickly re-establish populations within a year or two," Wein said.
While there are rats on main islands of Haida Gwaii, they aren't overrun with rodents like the unpopulated islands.
Rats are an invasive species that have had an impact all over the world, said Chris Gill, of the group Coastal Conservation, a partner with Parks Canada in the project, along with the Haida Nation and California-based Island Conservation.
"Right now, over half of all recorded extinctions are caused by introduced invasive species, and the biggest threat, the biggest contributor to the loss of species, are rats," he said.
The first aerial drop took place 10 days ago, and another will go ahead later this month. Volunteers are now combing the island to remove rat carcasses and reduce the likelihood other animals scavenge the poisoned remains.
It doesn't take long for recovery to begin, Gill said.
"It's amazing. Some of these islands where rats are removed you get species showing up within four months, changes on the island within four months," he said.
The rat poison is contained in compressed grain pellets dyed a green that is unattractive to other species, in an effort to minimize the possibility of poisoning other animals.
The amount it takes to kill a small rat would also have little impact on a large carnivores like bears, Wein said, and the poison is also being distributed later in the year, after many species have fledged their young and left for winter grounds.
In any event, the benefit to other species outweighs the immediate risk, both Wein and Gill agreed.
"There is always a risk of impact on individual animals," Gill said. But "it's a short-term impact for a long-term benefit."
Ancient murrelets are known as "night birds," and project Night Bird Returning began in 2009 with the aim of restoring the natural habitat on four of the Gwaii Haanas islands.
Two years ago, Parks Canada distributed poison pellets on two smaller islands in UNESCO world heritage site. This time, the terrain and large area of the two islands required the aerial distribution. While it's the first time it's been used in Canada, the method has been successful in New Zealand, the United States and Mexico.
If it works here, the eradication program may expand to other islands in the park.