With their hairless, rope-like tails and a tendency to hang out in the trash, rat sightings tend to make people uncomfortable.
Depending on where you live in Vancouver, you might see the skinny-tailed rodents frequently. In some places, their populations appear to be teeming -- but are they?
While they are frequently spotted, the actual or even rough estimate of the city's rat population is completely unknown.
The Vancouver Rat Project was started in 2010 by Dr. Chelsea Himsworth as a way to learn more about the rat population in Vancouver's Downtown Eastside, including about the diseases they carry. Before its launch, there had never been a comprehensive study of rats in Canada.
Dr. Kaylee Byers joined the project in 2013 to study how rats move around the city and used evidence-based monitoring to study their behaviour. The team set 10 Tomahawk traps (live traps) for each city block, covering nine city blocks at a time. The traps were set in the evening around 5 or 6 p.m. and then checked the following morning around 7 a.m. since rats are most active around dusk and dawn.
After the rats were caught, the team tagged their ears and collected urine, blood, and fecal samples.
"I spent a lot of time waiting for rats to pee," Byers tells V.I.A with a chuckle.
The team discovered that diseases rats carry vary drastically between city blocks because most rats don't move very far. In fact, a "happy" rat -- one that has all of its needs met, including a food source, water, an area to burrow, and access to mates -- really doesn't have any reason to move...and they don't.
Across the DTES, for example, one city block could have diseases in each individual rat, while the block right beside it could be relatively disease-free.
But most of the diseases rats carry in Metro Vancouver shouldn't alarm locals.
Diseases you can get from rats in Vancouver
Leptospirosis is a commonly found bacteria in rat urine that can cause flu-like systems in humans. While it can be quite serious, it can be avoided by staying away from places where rats live.
The study found that trapping several individual rats actually spurred an increase in cases of Leptospirosis, despite lowering the overall population on a city block. While they don't know exactly why this happens, there are several theories, including a change in a colony's social behaviour that results in new patterns of "fighting and biting," Byers explains.
The findings from the study pose issues for city-wide pest management since removing rats could have the unintended effect of increasing illnesses in people.
However, some viruses in rats did not increase as individual animals were removed.
Bartonella is transmitted by fleas and rats that nest communally. While individuals carrying the bacteria didn't decrease in city blocks where rats were removed, cases increased everywhere else. In other words, it was more of a preventative measure.
Byers notes that she studied the genetic material from 600 related rats and found similar DNA in 1,200 pairs of rats within 30 meters. In other words, rat populations can increase in a smaller space and don't move much -- unless something forces them to.
If you see a rat in your area, that is likely your "neighbourhood rat."
Is Vancouver's DTES the city's worst spot for rats?
When asked if there were more rats in the city's DTES than elsewhere, Byers admitted that no one knows.
Urban rats in Vancouver are one of two kinds. Norway rats, also known as brown, which live in underground networks of burrows and scurry along the ground. These are the ones you'll generally see in streets, hanging around dumpsters and other places where food scraps are available.
Black rats, also known as roof rats, move around higher places, including roofs, trees, and attics. They are commonly found feasting on rotten or fresh fruit from trees.
Norway rats are particularly hard to study because they live underground. The GPS on a tag might not send a signal once the rat dips back down, and they are often more difficult to tag.
While many people have studied rats in laboratories, Byers says doing so "fundamentally" changes their behaviour. Not only are the spaces much smaller, but also something like changes in light (rats are more active when it is dark), may cause a significant behavioural shift, Byers explained.
Despite being one of the most widespread and problematic pests around the world, there are still many questions about urban rat behaviour.
In the DTES, however, there are special risks for people experiencing homelessness. Since they are more likely to come in contact with rats, there is a greater risk to their physical health. Moreover, the animals can cause alarm for people who frequently see them or live in places with them; they can take a significant toll on mental health.
Is poison a good way to control rat populations in Vancouver?
Poison may be effective for eliminating rodents in some indoor situations but as a general rule, the use of a rodenticide causes more harm than good, according to the rat expert.
In an outdoor setting, rat poison poses a risk to the environment because animals that eat rats will ingest it, such as cats and coyotes. Similarly, poison can get into water.
"There are a lot of good reasons why people are scared of rats but managing rats in our environments is feasible. We need to think about how to keep them out of our homes," Byers said.
As temperatures cool off, Byers suggests you inspect the perimeter of your home to see if there are new points of entry and seal them accordingly. Mice and rats have hairs on their body that tell them they are safe if they have something touching their bodies, which is why they slink closely around homes. They aren't necessarily always looking for a way in, but are hunted by raptors, foxes, and coyotes and have "their backs always up against the wall" both literally and figuratively.
Rats typically live in attics, walls, basements, or other places outside of homes and use entry points to sneak in and score a meal, water, or nesting materials. This means that they are easier to keep out since they are coming and going frequently and the entry points can be located and blocked.
Traps might not always work on rats right away because they are neophobic, meaning they are wary of new things in their environment. The Vancouver Rat Project team left traps open for a week so the animals would get accustomed to them before they put stuff in them.
But not all rats are the same.
"I had a rat climb right into my hand," Byers recalls, expressing her shock at having a wild rat be so "friendly." In other instances, more aggressive individuals have "snapped" at the traps.
"From trapping about 700 rats, I can say they have their own unique personalities."
Newly arriving rats on boats may also "find it difficult to move into new populations" and rat battles may ensue.
Rats aren't always fighting, however. They live in colonies and thrive in fairly unproblematic-looking packs.
"When I was at a trap in an alley, there were so many rats running out of a dumpster and on the stairs," Byers explains, noting that not a single one of them entered her trap.
Have a look at a video of the rat party on some stairs.
