Canadian Park Biologists Aim to Eradicate Rats in Queen Charlotte Islands


The Queen Charlotte Islands, invaded by rats three centuries ago, are being restored to their original rat-free state to protect nesting seabirds from predation.

The Queen Charlotte Islands are a biodiverse archipelago and Parks Canada has been trying to restore the balance in the ecosystem by getting rid of rats, which seem to be the main culprits of hobbling the ecosystem.

The Queen Charlotte Islands were invaded by rats three centuries ago, and are being restored to their original rat-free state in a bid to save the beleaguered populations of nesting seabirds, whose eggs and chicks are eaten by the rodents.

The whole archipelago will be free of rats in the next year. If successful, these rat eradications would be the beginning of making 16 islands rat-free.

In late September 2012, crews on smaller islands tried to establish the minimal amount of bait needed to rid the islands of rats. The trials didn’t use rodenticide, but bait pellets laced with a biomarker named pyranine, which causes rodent urine and feces to glow green under UV light. After spreading a placebo nontoxic bait rates of 11 to 30 kg per hectare, the crew trapped the rats on the island to see whether they had taken the bait. Then they were euthanized.

Seabird populations are especially affected by rats, and half of all seabird species have declining populations. The Queen Charlotte Islands have more unique subspecies than anywhere else in Canada.

Rats were probably introduced by English and Spanish ships in the 1700s. With rats gone, the entire island ecosystem and nutrient cycle is expected to be restored since seabirds shift marine nutrients to forest ecosystems via their diet and defecation.

The rodenticide that will be used might kill other small mammals like deer mice and native shrews, but wildlife surveys have shown that they are not that prevalent, and even absent on some islands or exist at very low densities, probably due to being out-competed or predated by invasive rats.

This is the first time that rodenticide will be aerially applied in a forested North American ecosystem.

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