Most any park you visit is likely to be the home of a number of squirrels. According to this article at Gizmodo, this condition is the result of one of the very few examples where human beings have attempted to manipulate the ecology of an area with success.
Squirrels were introduced to urban parks beginning in the 19th century, because when people visited the parks the little critters were fun to watch and provided reminders of the country in the midst of city living. In fact, cities would plant nut-bearing trees in the parks to help create a habitat for the squirrels.
Squirrels are also big on college campuses, and the proximity of humans makes them somewhat bolder than the ones found in general neighborhood areas. At my alma mater, in fact, there were one or two fuzzy little bruisers disinclined to give way when you walked along one of the non-sidewalk trails.
So why are parks filled with squirrels? Because people put them there. It's the exact same answer if you replace "parks" with "Washington, D.C.," only this particular group of people are called "voters."