In 2021, the City of Boulder began using lethal control for prairie dogs on open space land in North Boulder. Now, city staff want to expand where lethal control can be used to include most of the city’s farmland.
This expansion would add several hundred acres to the existing nearly 500 acres where prairie dogs have already been removed, and another 400 acres where their removal is imminent. The goal, as explained by Tory Poulton, Boulder’s prairie dog ecologist with Open Space and Mountain Parks, is to address growing prairie dog colonies before they spread across the city’s leased farmland, theoretically avoiding large-scale kill-offs and the associated costs later.
On Oct. 5, Boulder City Council is expected to vote on whether to approve city staff’s request for the expansion. In a memo city staff provided councilmembers, they wrote that prairie dog colonization “threatens the viability of agricultural operations on portions of the OSMP system.”
Prairie dogs play a crucial role in Colorado’s ecosystem, earning the title of “keystone species.” Their tunnels aerate the soil and provide shelter for other critters, like burrowing owls and snakes. At the same time, they are a vital food source for eagles and ferrets.
But these rodents also wreak havoc on fields where people have altered the native ecosystem. When farmers till a swath of prairie, yanking out native species to plant non-native grasses for making hay and feeding livestock, it disrupts the balance that prairie dogs have co-evolved with over centuries.
“The prairie dogs tend to destroy whatever is growing,” Poulton said of the non-native grasses. “And there isn’t a supply of native seeds to replenish it.”
Because the European and Asian grasses planted for their high yields can’t handle the appetites of both cattle and prairie dogs, the city is left with fields of barren soil that can be carried away by the wind. Without proactive measures, Boulder’s open space becomes desert-like.
In 2022, prairie dogs expanded their colonies to cover over 5,000 acres of city open space, the largest expansion the city has recorded.
Cutting into the city’s bottom line
The City of Boulder leases some 16,000 acres of agricultural land to local farmers. When prairie dogs move onto some of this acreage, it can cause farmers to not renew their leases with the city. This not only results in a loss of city revenue, but also requires already-limited OSMP staff to take over responsibilities like managing invasive weeds, water usage and other property upkeep, the city’s memo said.
The memo explains that without having a farmer on a given plot, that plot can degrade, and fast. Unlike native prairie grass adapted to Colorado’s dry climate, non-native grasses planted on much of Boulder’s farmland depend on irrigation for survival. When there’s no farmer or available city employee watering those fields, the non-native vegetation withers and dies, leaving a skeletal field. Prairie dogs speed this deterioration.
According to Poulton, the city envisions a future where it would only require smaller, occasional removals of prairie dogs once it has successfully cleared the rodents from its agricultural land. After the initial push, the focus will turn to maintenance — addressing prairie dog colonies as soon as they begin to encroach. But that future isn’t here yet.
“We have at least a few more years where we have some pretty big lifts,” she said.
To save money, city staff are looking to bring the lethal control process in-house, meaning buying the PERC, or Pressurized Exhaust Rodent Controller, machine to pump carbon monoxide into burrows to kill the rodents. Thus far, the city has relied on outside contractors for this task, costing the city an estimated $50,000 a year. Boulder County already has its own machine and staff trained to operate it.
Ethical concerns of lethal control
Prairie dogs are highly social animals with intricate family structures and sophisticated communication systems. It’s therefore not surprising many people oppose gassing them. Even though the process is advertised as quick, it’s gruesome.
“The air in the burrow is purged very rapidly,” according to a company that makes PERC machines. “The rodent is engulfed almost immediately in a high concentration of exhaust gas and overcome before it has a chance to escape or block the burrow. This creates an airless condition in the burrow whereby the rodent is asphyxiated and killed via a lethal level of CO.”
For some time, the City of Boulder opposed killing the rodents that lived in Boulder before people. A city ordinance, passed in 2004 but since repealed, banned lethal control and instead required “humane methods” of relocation.
And since 2001, Boulder has also had an ordinance preventing even the disturbance of prairie dog burrows. This prohibition “protects active prairie dog burrows from being disturbed or damaged, including damage as a result of routine agricultural activities,” the city memo said.
The burrow ordinance has not yet been repealed, but as officials seek to expand the use of lethal control, city staff are looking to also relax the burrow ordinance. Protection for prairie dog burrows, Poulton said, is partly to blame for the proliferation of prairie dogs on city farmland.
Relocation remains an alternative for lethal control, but requires a place to put the rehoused rodents. And all the relocation sites within the city are at capacity. Even sites outside the city’s jurisdiction that previously received Boulder’s rodents, such as Rocky Flats National Wildlife Refuge and the Pueblo Chemical Depot, have either stopped taking in more prairie dogs or may soon, according to the city.
“Rocky Flats National Wildlife Refuge accepted prairie dogs in 2022 but did not in 2023,” the city memo said. “In 2023, relocations are underway to take prairie dogs from OSMP irrigated fields within the northern project area to the Pueblo Chemical Depot property. However, Pueblo Chemical Depot may not accept prairie dogs after fall of 2023.”
The city has said it’s committed to keeping prairie dogs alive in areas where they are welcomed, distributing a sylvatic plague vaccine to these populations, according to the memo. Sylavtic plague, the same bacterium that caused the black death in humans, is also deadly for prairie dogs.
And while seeking approval to kill one animal species, staff are trying not to harm others. On one prairie dog-affected field, for instance, eagles have been seen canvassing for dinner. Because eagles are a protected species, the field they’re hunting on will remain outside of staff’s scope.
“By the bald and golden eagle protection act, you can’t do actions that would impact eagles’ foraging behavior,” Poulton said.