May sound cheesy, but what about a group of Pigeon-weres? Some of the birds that learned how to turn themselves into human beings? Have some news reports mention the alarming increase in the amount of homeless in the city, which are really the birds learning how to spontaneously become human in appearance. This could lead a food shortage, which forces the pigeons and actual homeless to start stealing in greater and greater numbers? Can take this in any direction you want, maybe an all out riot starts among the homeless, etc etc.
Or indulge in the stereotype, and make it a little humorous with an ongoing war between the pigeons, rats, and roaches all fighting over turf and food?