Ah, rats — mild winter has a downside

Rodents squeaked through cold spells, now have city crews chasing their tails

Chicagoans rejoiced over the historically mild winter, but now many are experiencing the downside of no deep freeze: the pitter-patter of tiny feet in neighborhood alleys, the sound of a city’s rats thriving.

Complaints to City Hall about the omnivorous urban survivors — the bane of those who garden, walk dogs or loathe leathery tails — are on the rise.

Through the end of July, the number of calls to the city’s 311 center asking for a crew to get rid of rats was up more than 28 percent compared with last year. The raw figures: 15,895 calls this year, compared with 12,375 over the same period in 2011.

Department of Streets and Sanitation officials say they’ve put out more rat poison and are working more efficiently this year. Teams are responding within six days instead of an average of nearly eight days a year ago, according to city records. And the number of cases where crews put out poison to kill rats was up more than 19 percent, to 18,339.

One explanation is that brown rats, the area’s predominant species, likely rode out the chilly months with uncharacteristic ease, according to Steve Sullivan, senior curator of urban ecology for the Peggy Notebaert Nature Museum.

“Rats don’t hibernate. They have to forage for food year-round, which is much more difficult if there’s a lot of snow and the temperatures plummet,” Sullivan said. “So we usually see a significant die-off between their first and second year. It’s likely that didn’t happen this past winter, though, because we didn’t have that long snap of frigid temperatures with deep snow.”

Combine that with the furry rodents’ tendency to breed like rabbits and eat “anything humans can eat,” Sullivan said, and you have yourself a summer population boom.

ChiTrib