Chicago study explores rat contraception as safer alternative to poison

CHICAGO (WGN) — Chicago’s Lincoln Park Zoo is testing a new way to tackle the city’s rat problem without harming other urban wildlife.

Researchers with the Chicago Rat Project have launched a year-long study using plant-based peanut butter contraceptive pellets, created by the nonprofit WISDOM Good Works.

The trial spans a four-block area of Lincoln Park and aims to see whether contraception can shrink rat populations while reducing the city’s reliance on traditional poisons.

“The aim is to find out if contraception can help reduce our reliance on rat poison so that other wildlife isn’t as affected,” Dr. Maureen Murray, a wildlife disease ecologist at Lincoln Park Zoo, said.

Rat poison has long been the standard, but it comes with consequences.

A study found that 100% of raccoons, skunks and opossums collected from a local pest company tested positive for rat poison.

The issue gained more attention after a family of great horned owls near North Pond in Lincoln Park died from ingesting rat poison.

“One by one, the mother, father, and baby owl all died from rat poison,” Murray said.

The new contraceptive works by lowering sperm and egg production in rats. Murray emphasized it poses little risk to larger animals because the active ingredient is present in such small doses.

“A raccoon would have to eat fistfuls of it constantly to be affected,” Murray said, adding that feeding stations are designed with reinforced small openings to block bigger animals from accessing the pellets.

If effective, WISDOM Good Works estimates the contraceptive could reduce rat populations by 60 to 65 percent by the end of the study.