More Rat Complaints Mean More Rats, Lincoln Park Zoo Study Finds

CHICAGO — In recent years, Chicago has earned a bit of reputation when it comes to rats. That is, the city has lots of them. Lots and lots of them.

This summer, apartment guide RentHop named Chicago the U.S. "rat capital" thanks to the sheer number of rodent complaints from 2014 to 2017. And in October, Chicago was named the most rat-infested U.S. city by Orkin, the fourth year the city earned that particular distinction.

While Chicago's sprawling rat population is a bane to residents, all those rodents are a boon for researchers. Enter the Lincoln Park Zoo and its Davee Center for Epidemiology and Endocrinology and 2Urban Wildlife Institute, which teamed up with Landmark Pest Management, a research-based pest management firm, for a Chicago-based rat study.

"At Lincoln Park Zoo we are continually trying to understand human-wildlife conflict and find solutions to mitigate stress on both humans and animals alike," Maureen Murray, a wildlife disease ecologist, told Science X, a science news website. "Rats — whether or not we like it — are a part of our ecosystem. They are a fascinating species that we actually have relatively little research available on and we aim to change this."

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Since 2008, rat complaints in the city have risen 39 percent, reaching 45,887 last year. But using complaints to determine the concentration of rats in certain areas can be fraught with problems, such as socioeconomic factors unrelated to the number of rodents being the driving force behind the amount of reports made.

So zoo researchers decided to test the idea of "whether public rat complaints can serve as a reliable indicator of rat abundance to predict where rodent control is most needed," according to the study, which was published Wednesday in "Frontiers in Ecology and Evolution." To do that, they trapped brown rats in alleys in 13 out of 77 Chicago community areas "that varied from low to high measures of household income and urban development." Rat activity, rat attractants and the conditions of the alley and surrounding environment were all measured during the trapping, which ran between April 20 and June 20.

What researchers found was that rat complaints and a high population of rats do go hand in hand. Alleys with more trapped rats were found in areas with higher rat complaints, according to the study.

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Large concentrations of rats also were found in areas that had more "uncontained garbage" and a higher number of rental units. Areas with a large amount of vacant or abandoned buildings and lots had a lower number of rats, according to the study.

Those last findings lay out characteristics found in North and Northwest Side neighborhoods: high-density areas that also have a large amount of rat complaints.

"Additional research would need to be conducted but it seems that neighborhoods with high rental rates also had increased garbage and potential rat access points in alleyways, presumably due to the responsibility of maintenance being on the property owner rather than the tenant," Murray told Science X

Researchers hope the findings from this study, as well as continued investigations, could lead to better "proactive control techniques" for rats in Chicago and other cities around the world, according to the study.

But the study's biggest takeaway for Chicagoans is a simple routine to adopt.

"Stash your trash," Murray told Science X. "The easiest way to ensure rats stay at bay is to secure trash in closed bins."

Go to the website for "Frontiers in Ecology and Evolution" to read the complete rat study.

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