More localized rat surges can occur when a major demolition — such as the $850 million Ryan Field rebuild in Evanston — displaces rat colonies. In Chicago, rats are a widespread issue. Tree House Humane Society is pursuing a mutually beneficial solution to Chicago’s rat infestation through alternative placement for feral cats who cannot be socialized and adopted in a home. The Cats at Work program empowers property and business owners to care for a “colony” of feral cats to keep area rodent populations at manageable levels. Senior Community Programs Manager Cecilia Ocampo-Solis said Tree House runs the Trap-Neuter-Return program for cats who are unsocialized and can’t follow the “shelter to couch” transition. Tree House interviews and counsels “colony caretakers” for feral cats who will stay in backyards, warehouses and other non-residential sites. “People open their doors, truly, to these cats in hopes of controlling the rodents. But from a Tree House standpoint, it’s a symbiotic relationship,” she said. “The client gets rodent control that is probably cheaper than getting a company to come once a month (and) not working, and then the cats get that second chance where they have this person who now cares for them.” However, some have called the efficacy of this program into question. Karen Anderson has lived in Lakeview, a neighborhood on Chicago’s North Side, for over 20 years. She said her neighbors took on a pair of cats via the Cats at Work program, but they soon began showing up in her yard to eat the birdseed she put out. After seeing how skinny they looked, Anderson began leaving out water and canned cat food for them. “(My neighbor) said, ‘Well, I put food out, but the rats just eat it. I got those cats to get rid of the rats, and now they’re having opposite effects,’” Anderson said. Anderson has fed the feral cats for more than two years. She has also stopped putting out birdseed for fear the pair will hunt birds — prey she said many cats seem to prefer over rats. According to Ocampo-Solis, the Cats at Work program is working to help “second chance” cats coexist with birds by not placing these cats near parks and requesting that caretakers don’t put out birdseed or bird fountains. “Tree House believes that there’s room for everyone at the table,” she said. “There’s always going to be different things to advocate for, and we want to work in harmony with people that are advocating for bird migrations and bird presence.” Other neighborhoods have experienced success stories. Ocampo-Solis referenced the “CongRATS Monica. 50 rats gone!” sign hung in Logan Square that celebrated a cat adopted through the Cats at Work program who helped a family exterminate a rat colony living under their HVAC system. Although the impact of this program across individual neighborhoods can vary, the number of stray cats taken in by Chicago Animal Care and Control has increased 180.65% since it hit a low of 2,993 strays in 2020. Robyn Detterline, a board member of the Chicago Ornithological Society, said cats are also major threats to migrating birds. Although Detterline has a foster cat, she said programs that release cats into the outdoors harm bird populations while not effectively controlling rodents. “The cats are not eating the rats; the rats are just moving to the next block,” she said. Chicago Bird Alliance President Judy Pollock said the nonprofit’s rodenticide task force got a boost when three big-horned owls that had a highly visible nest in Lincoln Park died from rat poisoning in August. The CBA has spoken against using anticoagulant rodenticides, also known as second-generation rodenticides. These rodenticides interfere with an animal’s ability to cycle vitamin K and clot blood and are dangerous to wildlife that consume the poisoned rats. Without the ability to clot blood, the poisoned rodent — or any animal that consumes the toxin — experiences internal bleeding. “They’ve been making these stronger rodenticides lately, and they’ve also sort of found their way onto shelves so that basically anybody can buy them,” Pollock said. Detterline said this is especially harmful in Chicago, which is en route for many migrating birds — including endangered and threatened species. “We’re in the middle of what’s called the Mississippi flyway … where birds are funneling up the Mississippi on one end, but on the other end, Lake Michigan,” she said. “When the birds are coming up south or are going north, they all kind of funnel around the lake. There’s just a ton of birds that come through here every year, and they love our lakefront.” According to a 2024 study published in Science of the Total Environment, biomagnification of anticoagulant rodenticides is also a concern for “mesopredators” and scavengers like skunks, raccoons and opossums. Of the 101 brown rats from Chicago alleys tested in the study, 74% tested positive to at least one AR compound and 32% were exposed to multiple AR compounds. Of the 93 sampled mesopredators, 100% were exposed to at least one AR compound and 79% were exposed to multiple AR compounds. The percentage of rat complaints from an alderman’s office has increased from just over 3% in 2019 to over 20% so far in 2025, possibly indicating elected officials are getting more involved with the problem. A representative from the Bureau of Rodent Control declined to comment on the status of the carbon dioxide rodent control method, but confirmed that no special funds are set aside for the project and the money would come from the regular rodent control budget. These alternatives would help mitigate the need for rodenticides that harm non-target wildlife. Ocampo-Solis said Tree House is evaluating potential updates for a 2007 ordinance that permits feeding outdoor cats in Cook County, as long as they are spayed or neutered. She said Chicago residents should practice “consistent feeding,” or feeding outdoor cats at the same time every day rather than leaving food out where rats can get into it. She added that they should keep an eye out for strays as kitten season approaches. Detterline, who describes herself as both a “cat person” and a “bird person,” said she hopes different advocacy groups can work together to discuss these issues and solve the rat problem, despite tensions between the solutions they put forward. Pollock said cleaning up after dogs, strategically containing garbage and not throwing food waste or bird seed in yards can also help reduce the rat population. “We really have a lot of solutions because there’s not a silver bullet for this,” she said.
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