Rich, you think 50,000 rats is an extremely low number? Okay. Orkin has named Chicago the rattiest city in America for three of the past four years, so if Orkin's numbers are low for Chicago, their numbers are probably low for every other city. Nevertheless, Chicago is still the rattiest city according to Orkin. 

And if you don't believe the Humane Society of the U.S.'s estimate for feral cats (1 for every 10 residents) because you think they are tired of euthanizing pets, how about two researchers who have been studying feral cats for decades and are sympathetic to TNR programs who find it reasonable to estimate a community's feral cat population at 1 cat for every two households, or nearly twice as many as the HSUS estimate. Like I say, these are just estimates, but I used the most conservative ones I could find and your estimate hinges on a wrong turn in a single Chicago neighborhood a number of years ago.