Getting too comfortable in Billings city parks, a growing population of Richardson ground squirrels has been served with an eviction notice.

Commonly mistaken for gophers, the furry little diggers have pockmarked recreation fields with entrances and exits to their complex subterranean habitats.

The tunnels have created headaches for field maintenance workers and a hazard for the ankles of athletes using the fields for sports.

“They’ve taken over so badly,” said Steven Pabich a parks department employee who was holding a hose that spewed a mixture of masonry sand and water into a burrow at Amend Park on Friday. “I know I’ve rolled my ankle in a couple of (holes).”

The machine mixing the slurry, dubbed the Burrow Blocker, is the newest weapon to fill in the thousands of holes the ground squirrels have made in city parks.

“From observation in the Amend Park area,” Billings Parks Department Superintendent Jon Thompson said, “I’m sure we’ve got 1,000 squirrels in that area.”

The Burrow Blocker, which cost the city $22,000, mixes sand and water in a hopper and then pumps it through a hose for delivery in the holes.

Once water is absorbed, the sand is left behind filling the squirrel’s burrows and preventing them from entering or exiting.

“It’s safe for dogs and kids, and they can play soccer on the fields right after we’re done,” said Parks Supervisor Mike Pigg, who has been keeping an eye on the operation.

In about two hours, the rig can go through its capacity of 500 gallons of water and 2 cubic yards of masonry sand.

“This is really only our third day of going,” he said. “I bet you we’ve filed 1,500 or 2,000 holes.”

“Some of the tunnels are so deep and so complex,” Pabich said. “There was one hole we pumped for about 15 minutes.”

Pest management techniques have varied over the years to control the squirrels, which dine on green grasses common in the eastern side of the Continental Divide.

“Back in the day, 25 or 30 years ago, it was legal to lay poison baits like oats,” Thompson said. The poison was extremely effective, but also killed non-target animals and posed a danger to pets.

Anti-coagulant products, like Rozol or Ramik Green, also were outlawed for non-target deaths, and about four years ago phosphine gas tablets were severely restricted after improper use beneath a home in another state killed two children, Thompson said.

The only other feasible option in the city is carbon monoxide gas bombs, which are about 30 percent effective and cost $6,000 to $8,000 an application.

“We potentially would have spent $22,000 just (at Amend) and maybe not get them under control,” Thompson said. The Burrow Blocker will allow them to come back time after time to keep the populations down.

Masonry sand, Pigg estimates, costs about $15 per yard.

As the squirrels wake up from winter’s hibernation and begin mating, the population will again increase.

“If every female has six or seven, you can increase your population by 600 percent in a year,” Thompson said.

Killing lots of critters isn’t appealing to anyone, and wildlife is welcome in parks, but when a species becomes a nuisance it needs to be taken care of, Thompson said.

A few water-logged squirrels have managed to escape and that’s OK, Pabich said. “They come up, and you let them go.”

They can live to dig another day on other land, just not where people play sports.

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Chris Cioffi covers city news for The Billings Gazette in Montana.