The latest weapon in Chicago’s war against rats is plant-based, naturally flavored and nutritious.
It’s a birth control pellet made with corn and peanuts, and a team of researchers and volunteers will be serving it to discerning rats in a four-block area of Lincoln Park for a year.
The aim is to reduce the rat population without harming urban wildlife, including owls and hawks, which can die after eating poisoned rodents.
The study was sparked by the high-profile deaths of three beloved Lincoln Park owls — mom, dad and owlet — who made their home near North Pond and died in rapid succession last April and May. The deaths were all linked to rat poison, which causes internal bleeding.
“We just realized we had to do something,” said Judy Pollock, former president of the Chicago Bird Alliance, which raised $32,000 for the study and is working with partners including the Lincoln Park Zoo, the Chicago Department of Streets and Sanitation and 43rd Ward Ald. Timmy Knudsen.
The Chicago study comes at a time when the poisonings of high-profile birds of prey have helped launch rat contraception studies in New York and Boston.
New York lost Flaco the Eurasian eagle-owl, who famously flourished in the city after escaping the Central Park Zoo, to a 2024 building collision. But testing showed Flaco had been exposed to a level of rat poison that would have been “debilitating and ultimately fatal” even without the accident — and may have made the accident more likely, according to the Wildlife Conservation Society.
In 2023, a barred owl known as Owen was rescued near Boston’s Faneuil Hall after ingesting rat poison. Owen lost an eye but survived.
The Lincoln Park owls nested in an easily accessible park, and some fans would visit them on a daily basis.
Then all three owls died in the course of a single month.
“It was really sad and there were a lot of people that watched it and as a result, I think, a lot of people are very interested in our work,” Pollock said.
The contraceptive pellets, which are distributed in black feeding stations about the size of a traditional rat-bait box, look a lot like dry cat food and are sized for carrying (by a rat). The active ingredient is an extract of thunder god vine, an Asian plant that has been used for centuries in traditional Chinese medicine.
Thunder god vine, which is used to treat inflammatory diseases such as rheumatoid arthritis, has a notable side effect: It can decrease fertility, according to Alaina González-White, director of operations at Wisdom Good Works, the Arizona nonprofit that is supplying the contraceptive used in the Chicago study.
The Wisdom Good Works contraceptive targets both male and female rats, González-White said, interrupting ovulation in the females and inhibiting sperm development in the males.
While standard rat poisons accumulate in the animal’s body, the active ingredient in the Good Works contraceptive is rapidly metabolized in the rat’s liver. The rats need to continue to consume the pellets to maintain the contraceptive effect.
The contraceptive is formulated for rats and mice, so other animals would have to eat very large amounts to be rendered infertile, and even then, the effect would be reversible, according to Wisdom Good Works founder Loretta Mayer, who spoke at a recent webinar hosted by the Chicago Bird Alliance.
Mayer, the co-inventor of the contraceptive, which is called Good Bites, said that Wisdom Good Works hasn’t seen any negative effects on birds, dogs or squirrels.
During a study in the historic Jamaica Plain neighborhood in Boston that began in 2023, the rat population declined by 56% to 70% over the course of 16 months, Mayer said.
Asked if Chicago could expect similar results, Mayer quipped: “Well, if I knew that I’d be in Las Vegas, making my fortune. Our experience tells us that … a 50% reduction would be an expected reduction.”
She added, “If I were a betting woman, I’d probably bet somewhere around a 60-65% reduction level.”
Contraceptives address the great challenge of rat control: the animals’ rapid rate of reproduction, according to Maureen Murray, assistant director of the One Health initiative at Lincoln Park Zoo.
Murray, who is leading the Chicago rat contraception study, said rats can breed every three weeks, and they produce up to 12 pups in a litter.
Two rats can produce about 1,250 rats in the course of a year, according to the global pest control company Rentokil.
Killing a rat does, of course, end reproduction, but it’s incredibly difficult to kill enough rats to make a lasting dent in the population, Murray said. And when you kill rats, the remaining animals will multiply faster, because they have more access to resources such as food.
The Chicago rat contraception study will monitor the effects of the contraceptives using multiple measures. Researchers will look at how much of the contraceptive is consumed, how many rats are visiting the feeding stations, and how much rat activity is picked up at separate stations dubbed rat cams.
The rat cams — upside down buckets with wildlife cameras hanging from the “ceiling” and peanut butter inside — will be stationed in areas where rats travel, such as along fences. Small holes in the buckets will allow the rats to enter and exit.
The researchers will also be using the rat cams to monitor four neighboring blocks where contraceptive pellets won’t be distributed. That’s to help assure the researchers that any drop in the rat population in the area with pellets is due to contraception, rather than broader factors such as weather or sanitation.
A rat’s range varies, but the animals typically stay within an area smaller than a city block.
A 50% reduction in rats would be a great outcome for the study, said Gloria Pittman, Chicago deputy commissioner of the Department of Streets and Sanitation, at the Chicago Bird Alliance webinar.
Streets and Sanitation helped choose the areas where the contraceptive is being placed and is part of the team that is monitoring the results.
Knudsen, the 43rd Ward alderman, said in a news release that if all goes well with the study — and he believes it will — he wants to pitch a citywide rat contraception program.
“It would be great if contraception could be one of the tools in the tool kit for rats,” said Murray. “I’m not sure that any one single tool is going to be the best in all scenarios, but I think having another tool so that we are less reliant on rat poison will benefit everyone. It will benefit people, it will benefit pets and it will benefit wildlife.”