HARTFORD, Conn. — Connecticut’s capital city is testing out a kinder, gentler approach to reducing the rat population in Bushnell Park, with a strategy straight out of school sex education.

Every week, Hartford fills 30 lunchbox-sized bait stations with rat birth control to prevent the rodents from doing what they do best — multiplying, at a rapid rate. If left unchecked, a pair of brown rats can produce 1,250 descendants in one year, a continual problem too big for cities to combat with poison and other forms of lethal pest control.

After decades of reliance on rat poison and more recent use of dry ice, Hartford has joined cities like Washington, D.C., San Francisco and Los Angeles in deploying the sweet-tasting, high-fat ContraPest, a liquid contraceptive that temporarily makes male and female rats less fertile.

This approach also avoids the pitfalls of poison — that the rats who eat it and survive build up a resistance that they pass on to future generations, while others are smart enough to avoid the food sources that sickened other rats.

“The bottom line is you’re never going to get them all and the ones that remain are either smarter or more resistant,” said Ken Siegel, CEO of SenesTech, the Arizona-based company behind ContraPest. “You wind up with a vicious cycle.”

Over time, birth control brings rat numbers down and keeps them down, according to SenesTech, which developed the product for use in agriculture, zoos and animal sanctuaries and cities.

Contraceptive also carries less risks to the environment than rat poison, which can be equally toxic to pets and wildlife. Long-term studies are ongoing, but Siegel says his product has low levels of active ingredients, and they quickly leave a rat’s system.

It’s “very unlikely,” he said, that ContraPest would have any effect on the hawks and neighborhood cats that prey on rats.

Hartford began piloting the rat contraceptive in the spring, targeting the 37-acre Bushnell Park where people held picnics throughout the COVID-19 pandemic, and turned out in the thousands this year for the return of concerts and festivals.

A state grant has paid for the initial pilot program in Hartford.

The city had hoped to start the pilot in the spring of 2020, but it was delayed by the health crisis.

Now, more than three months into the program, early signs are pointing to success, Siegel says.

Consumption of the bait is high across the 30 stations in the park, and rat sightings and citizen complaints are down significantly, he said. In the next few months, Siegel said he hopes to see rat burrows disappear.

He could not provide any statistics and said SenesTec is still exploring how best to measure how much of the bait rats are drinking.

Hartford is only the second city on the East Coast to use ContraPest, one of several producers of rat birth control. The company’s first client on this coast was the nation’s capital, where a four-month study showed rat populations declined by 51 percent to 88 percent in the areas it targeted.

“Hartford was the first one post-Washington to essentially raise their hands and say, ‘We’re ready to go,’ but we continue to talk to others in New England,” Siegel said.

D.C. expanded its use of rat birth control last summer.

Siegel said he hopes Hartford will also expand beyond Bushnell Park into areas with dining and housing, particularly spots where restaurant closures during the pandemic forced rats to look for new sources of food and shelter.

“It’s an ideal time to deal with them as the rats branch out further,” Siegel said.

Like any city, Hartford has always struggled to control its rodent population. But Hartford Health Director Liany Arroyo says the problem did seem to grow during the pandemic, because dumpsters at restaurants were suddenly empty and most people were at home, leading to more sightings.

There was also a few-months period in the summer of 2020 when the city was not baiting for rats at all because of a shortage of inspectors, Arroyo confirmed.

That situation was temporary, and use of rat poison and dry ice has continued in addition to the rat birth control pilot, she said.

The city also switched rat poisons this year to counter rodenticide resistance and inspectors are using different strategies to get the bait deeper into rodent burrows, where it should be more effective, Arroyo said.

Story by Rebecca Lurye, Hartford Courant.