"Chicago weather officially too cold for polar bears"

Chicago's cold temperatures on Monday were too cold for zoo polar bears, that is.  And for good reason - the Lincoln Park Zoo's polar bears don't have a layer of blubber because it would be way too hot for them during the summer. They aren't eating whale carcasses and seals and so don't create a thick layer of fat, which means they will get colder than wild polar bears in extremely cold temperatures and need to go inside their heated dens.

Ron the bison looks quite content in the chill, though.

http://www.huffingtonpost.com/2014/01/07/chicago-weather-cold_n_4556042.html