Why a cold winter won't slow Vancouver's booming rat population

According to the Chinese zodiac 2015 was the year of the sheep.

But in Vancouver, according to pest control companies, 2015 was the year of the rat. Again.

Mike Londry ofWestsidePest Control says rat call-outs outstripped other critter complaints last year by a largemargin. He believes a string of mild winters has beenfuelling Vancouver's rat boom.

"It lets them get outside and foragewhen they normally would be hunkering down and clinging to life," he told CBC, noting that rats are appearing in places they've never been seen beforeoften in broaddaylight.

"They're now thriving 12 months of the year," he said.

Chelsea Himsworthof the Vancouver Rat Project says warm winters may give a minor bootto rat numbers,but even if Vancouver experienced a "winter to end all winters,"it's unlikely the population would drop by much.

"Cold is not a protection against rats," said Himsworth, an assistant professor atUBC'sSchool of Population and Public Health.

"Great evidence for this is that rat populations are thriving in Scandinavia and Iceland which are very far north and extremely cold." she added. "And they're the exact same kind of rat that we have here, the invasive Norway rat."

HimsworthbelievesVancouver's rapid densification is more likely the culprit.

"Rats depend on humans for food and places to live, soreally we determine the size of the rat population," she said.

Himsworth saysanecdotal evidence fromexterminatorsis a good indication therat population is growing andbelieves the cityneeds a municipalstrategy to both measure and control the problem.

"Right now, the exterminators are like [fire truck]drivers. They're going around the city putting out fires, but we have no plan in place to deal with the larger problem," she said.

New York recently adopted a multi-million dollar rat control program, launching an assault on the likes of "pizza rat"and its numbers, whichhave famously plagued the city for years.

Vancouver's rat problem was a minor issue during the last municipal election with various politicians pledging to address it, but the issue hasn't received much attention since.

Londry says a critical components in controlling rats is controlling garbage, especially with Vancouver's growing green bin food scraps collection program.

But even then, he doesn't expect the rat calls to stop coming inanytime soon.