Rats! Black Rat spreads to BC Interior (2014)

by Margaret Holm, Okanagan Similkameen Conservation Alliance

Unfortunately, the sailing ships that brought explorers and settlers to British Columbia also brought rats and mice. For a hundred years or more the large Norway Rat and Black Rat species were confined to coastal areas, but in the past decade, the smaller Black Rat has spread to the interior of the province and is a new problem in urban and rural areas.

The black rat, or roof rat, has a tail that is longer than its body. It nests in sheds and attics and is an excellent climber, using pipes, wood siding and wires to clamber into small holes and chew through plastic vent covers and screens to gain access.

A pair of black rats can produce six litters a year so you definitely want to be prepared if you have heard that rats are living in your region. Trapping is effective for small populations and is the preferred method over the use of poisoned bait, which can harm non-target animals such as domestic pets, hawks, owls and snakes. Since snakes and raptors are doing us a favour by preying on rodents, we should make sure that our pest control methods are not harming these native animals.

Rodent control for all species involves controlling food attractants, limiting access to building for nesting and shelter, and having snap traps set in key locations. Snap traps are a safer and a better choice than using poisoned bait. Rats require the use of a larger snap traps designed for their body size. Ideally the trap is placed in corners along inside walls. Ideally the traps are enclosed in plastic tubing or a wooden box. Two traps facing out are effective but make sure the space is large enough for the mechanism to snap and to be easily set again.

Rats like fresh foods and will reject spoiled or rancid food. They are also smart and find ways to steal from traps. Rodent food bait, such as a slice of fruit or vegetable with peanut butter, should be placed securely on the trip mechanism or even wired on. Check the traps daily and leave them in place as a preventative measure even after rodents are trapped out.

The best practice is to make your property unattractive to rodents by being aware of food sources and building access points. Keep garbage and edibles in containers with tight-filling lids. Place traps under lumber, pallets and debris which are common nest spots as well as sheds. Based on field tests, ultrasonic devices have insufficient repellency to merit use.

If preventive control measures and trapping are not adequate, poison baits may be necessary. Treated baits should be placed in in covered, tamper-resistant bait stations or in locations not accessible to children, pets, wildlife or domestic animals. Bait stations can be built or may be purchased commercially. Entry holes should be sized for target animal, no larger and interior baffles or small openings should prevent people from touching the bait. Lastly, anchor the bait stations to the ground and flag. Never scatter bait outside a bait station or rodent burrow.

Make sure the bait stations are checked regularly and dispose of dead animals daily to prevent other animals from being attracted to and eating the carcass. To reduce exposure of non-target birds and other wildlife to poisoned carcasses, dead rodents should be securely wrapped and placed in closed containers for disposal or buried to a depth that will make them inaccessible to scavengers.

Sadly, recent studies of Great Horned Owl and Red-tailed Hawk carcasses found in locations across Canada, showed significant levels of anticoagulant rodenticide chemicals in the livers of the dead raptors. Researchers estimate that use of rodenticides is an unintended but significant threat to hawks and owls. Since rodents may need several feedings of bait before they succumb, they can become a poisonous meal for snakes and raptors. Some rodent populations have become resistant to certain poisons. Snap traps may require a bit more effort but it’s safer and supports species doing rodent control the natural way.

Check out “Living with Wildlife”, a series of nine wildlife management guides for agriculture published with the support of the BC Agriculture Council at http://osca.org “Living with Wildlife” pages.