City To Offer Rats Delicious Contraceptives, But Science Is Unclear

UPPER WEST SIDE, NY — A new bill proposed by an Upper West Side City Council Member seeks to ban the use of rodenticide in the city's war on rats.

Those deadly drugs, Council Member Shaun Abreu said, just don't work.

The recent death of the beloved released Eurasian Eagle Owl, Flaco, found with raised levels of rodenticide, was a wake up call, says Abreu and a coalition of bird-minded colleagues and organizations.

"The cost to pets, birds of prey, and other wildlife is too great for a method that hasn’t produced tangible results," Abreu said.

He introduced a new bill this week to have the city try a different idea to fight the rats: birth control.

A new soft-bait product by rodent birth control pioneer, SenesTech, could prove palatable enough for city rats to curb their birthrates, the company told Patch.

"Rat birth control is a promising non-toxic solution to remediating heavily infested areas without dumping lethal poisons all over our city’s streetscape,” Abreu says.

His office told Patch that the cost of the 10-block pilot will be determined later. A report pegs the bait at about $5 per pound.

The only problem? Experts claim that rat birth control — just like rodenticide — has not produced measurable results in an urban setting.

Struggles in the big city

Some rodent experts are stoically skeptical of claims that the better mouse — or rat — trap has finally been invented.

Rodent scientists told Patch that, in an environment like New York City, the main challenge is that rats have too many food sources to pick from, and the open populations of rats in the city means it might be impossible to have a measurable effect unless done to a massive scale.

Multiple trials with rat birth control in different cities around the country — Washington D.C. and New York City, notably — have not produced clear results showing its field efficacy.

Those trials, including several in New York City, resulted in discontinuing the use of an earlier SenesTech product, a more expensive and harder to use liquid product called ContraPest.

One issue is a lack of published scientific evidence on the efficacy of rodent birth control in research journals, aside from a sole study of roughly a dozen bait stations at two Washington, D.C. locations.

A previous SenesTech trial of the liquid product, ContraPest, performed in MTA refuse rooms cites an extremely wide range of rodent reduction — between 18 and 67 percent. The trial noted that rodenticide was also in use at the locations.

Another short trial in Bryant Park last year yielded no results.

“Good optics is not a substitute for sound science,” one rat expert told Patch.

A neighborhood rodent group in Prospect Heights told Patch that they think it’s a “headline-grabbing distraction,” according to Jesse Hendrich, a founder of the Sterling Committee on Rat Awareness and Mitigation — or SCRAM.

Hendrich said their group would “much rather see [carbon monoxide] treatment made free for the city,” to treat specifically acute rodent burrows.

“Of course, the main reason they persist is food and harborage,” Hendrich said. “Cleaning our act up (literally) with new sanitation and outdoor dining practices will deny them easy access to food and shelter, and thus is the best way to address the issue in our opinion.”

The gourmand’s dilemma

Rodent expert Matthew Frye, of the New York State Integrated Pest Management program at Cornell University, agrees with Hendrich — at least on what the city’s main rodent battle plan should be.

And while he is a bit skeptical about how well rat birth control will work, he’s not entirely dismissive of the new product, saying SenesTech’s soft bait formulation should perform better than the liquid product, due to ContraPest’s bait longevity.

Dan Palasky, the Chief Technical Officer at SenesTech, says that the new soft bait product, called Evolve, could help reduce rodent populations by 50 percent in six months.

“If you've gotten the whole population on birth control, you should see close to a complete elimination of that population in 12 to 18 months,” Palasky said. “You're not controlling the death rate. You're controlling the birth rate.”

For contraceptives to work in rodents, a lot of them need to consume the bait both enough and regularly, Frye said.

“The difference between this approach and rodenticides is that rats only have to consume a lethal dose of rodenticides one time to remove them from the population,” Frye said of the deadly poison, “which would also stop their breeding.”

And a huge number of rats would need to be hooked on Evolve, Frye said.
“That is a tall order in environments where other food sources are available,” he told Patch.

The taste rats love

While they haven’t done a side-by-side test of their two rodent birth control products, Palasky said that “anecdotally, Evolve seems to be more palatable to rats every time.”

The active ingredient in Evolve, a minimum-risk pesticide with no known toxicity, Palasky said, is cottonseed oil, which impacts both male and female fertility — but does not sterilize rodents. The bait is an allegedly irresistible combination of grains, fats and sweets.

A trial with Evolve on a sugarcane farm had a surprising result. Despite the ready supply of tasty sugar, “they ate all of our bait in three days,” Palasky said.

But a farm is a less complex environment than a city, with far fewer dynamics affecting populations.

The sole published study on rodent birth control, published in the Journal of Pest Science in 2023 by a Northern Arizona University scientist, included examining two small field trials in Washington, D.C. where, the paper claims, visible rodent populations were reduced.

Results varied at each site. One major factor cited is that some rats are just not that into bait stations, regardless of the treats.

“Contraceptives could help,” the paper says, which was supportive of the method, “but their efficacy on rodenticide-resistant populations is poorly known.”

Like with other trials, rodenticide was also present in the environment. Two named authors were either current or former employees of SenesTech, and a third is a former chairman and chief scientific officer to the company.

Frye says that containerization and proper sanitation, seen as the only real road to rat reduction in urban settings, could result in less trash and more birth control in the rat diet.

“I'd love for all the rats to eat a pound of it in the first week,” Palasky said. “But if they only eat a couple of grams here and there,” he said, fertility could still be affected.

Abreu agrees, and says that’s why now is the perfect time to test out a new product in the rat war that won’t extend the front to the city’s beloved large birds.

“Rat birth control must go hand in hand with better trash management, which is why the time is ripe for New York City to test this proposal,” Abreu told Patch.

Looking for love in a trashy place

If you’ve ever traveled across multiple subway lines and two boroughs over for a date, you’re not alone.

Turns out, rats will traverse for love, too.

The rodent scene in New York City is what Frye calls an “open population,” where, according to research, individuals can travel distances in order to mate.

That means rats not exposed to the bait can come in and replenish populations in a matter of months, due to their prolific breeding.

Abreu’s pilot will target a 10-block area with a six-month study to gain a baseline understanding of rodent populations, followed by six months of birth control.

Migratory rats are also a big challenge when it comes time to assess the efficacy of trials, Palasky said. Frye adds that rodenticide has the same problem.

Special cameras and bioluminescent bait could help figure out which rats are eating the contraceptives, Palasky said, but it’s still a struggle.

“If you don't have an isolated area, you are going to get migratory rats in that area as resources open as you lose population in that area,” he told Patch. “That is always a challenge.”
Both Frye and Palasky agree that any rat war needs multiple fronts.

Any of the past field studies with ContraPest, Frye points out, were done concurrently with rodenticides.

“In other words, they are not using this as a replacement, but an additional control measure,” he says. Palasky said that as a company, they advise using birth and death strategies side by side.

For the new Evolve product, Abreu’s proposed pilot will be the first urban trial of its efficacy.

The success of that pilot, advocates and experts say, should not change the city’s need to cease using environmentally hazardous rodent bait.

"We can't poison our way out of the rat problem,” Abreu said, “but we can certainly do a lot of damage trying."