Gopher snake
Gopher snakes are perfectly designed to get rid of the pesky pocket gopher. But sometimes, both the gopher and the snake fall victim to harmful poisons.
Pocket gophers! Rarely does one animal raise such ire in gardens, vineyards and orchards. Pocket gophers are native rodents that spend most of the day underground, emerging at night to eat tasty stems, leaves, and bark. They don’t hibernate and spend considerable time feeding above ground in spring and early summer. As a crop’s roots develop, they feed more underground, creating shallow burrows as they search out food. Shallow tunnels are used for their food searches, while deeper burrows are used for their litters.
If it wasn’t for snakes, owls and hawks, we would be knee-deep with rodents. Each of these predators has a role to play in agriculture. Gophersnakes (or bull snakes as they are often called), like nothing better than to go down a hole and investigate what lives below. They are constrictors that kill their prey by squeezing them to death. Racers are fast-moving pale gray snakes with no markings. These swift hunters are on the lookout for rodents. Luckily all snakes can unhinge their jaws to swallow the fat-headed pocket gophers. The first time I encountered a Racer it had a pocket gopher halfway “down the hatch”.
Great Horned Owls are the largest owl nesting in British Columbia. They patrol a large area every night on the lookout for larger prey like pocket gophers and rats. Barn Owls are rare in the interior but common in the Lower Mainland. Each night a pair of owls will catch three to six rodents for each of their young as well as themselves. That’s 15 to 30 rodents a night!
These predators aren’t the only ones out to get rodents. Humans do a good job as well, as evidenced by a 2010 Environment Canada study. Unfortunately, many of our methods at best do nothing at all, or at worst, end up harming not only the intended victims, but their unsuspecting natural predators as well.
A 2010 Environment Canada study examined the bodies of dead Red-tailed Hawks and Great Horned Owls collected from across Canada. All the owls had compounds in their livers from rodenticides, including anticoagulants used to kill rats.
Poisoned baits are used for rodent control but can poison other wildlife. Strychnine and zinc phosphide are incorporated into bait pellets which are put down tunnels to kill pocket gophers. Once the bait is eaten, the rodent will die quickly. Most snake species smell their prey and will eat dead rodents, so if a gopher snake ingests the dead pocket gopher there is a good chance that it too will succumb to the poison.
Studies have shown that pocket gopher burrows are re-occupied by other members of the species within hours. Therefore, it makes sense to use a control method that doesn’t harm the natural “gopher getters” that are on the job all day eating rodents. Some people try flooding the tunnels with water or setting off sulfur bombs. Both methods are listed as ineffective by Agriculture Canada. Another popular option is purchasing blasters that ignite a mixture of propane and oxygen in the burrow system. This concussive force kills the gopher and destroys the burrow system but will also kill any snakes nearby. Additionally these devices can cause unintended damage to property and there is a danger of fire in the summer.
By far the least dangerous method of pocket gopher control is trapping with either tunnel traps or cinch traps. Trapping strategies include starting in the spring as population build rather than waiting for numbers to get out of control and focusing on one area at a time and trapping at the freshest sites first.
An effective strategy is to methodically use several traps in one area before moving to another site. Trap all year long to make sure the population is low to zero. Lastly, stake traps to find them and monitor often since traps can get filled with dirt.
Two trap designs are commonly sold – the enclosed trap and the cinch trap. Enclosed traps (enclosed inside a plastic tube) are used in pairs inside a runway facing in either direction. The cinch trap is best used at the burrow entrance, and is easier to set and check than searching underground for buried traps. Both traps kill quickly and don’t require poisoned bait.
There is no question that trapping requires more work, but at least you know you’ve done the job. One doesn’t necessarily find out if poisoned bait has been effective and there is always the danger of wildlife, dogs and cats eating the poisoned bait. By staying away from poisons you can sleep at night knowing that the snakes and owls are helping do the work for you.
Margaret Holm works at the Okanagan Similkameen Conservation Alliance, one of 50 groups working to keep nature in our future in the Southern Interior.