An interesting article from 2014 about how the urban squirrel is a human creation:
In his paper, Benson quotes an 1853 Philadelphia newspaper article describing how introducing squirrels and other animals would help turn public squares into “truly delightful resorts, affording the means of increasing enjoyment to the increasing multitudes that throng this metropolis.”
At the time, squirrels were so rare in urban environments that when a pet squirrel escaped from a home in New York City in 1856 and sought refuge in a tree, it drew hundreds of excited onlookers.
While the earlier introduction efforts failed — some cities culled the squirrels, concerned about their impact on birds and on potential tree damage — the second ones took. Landscape architects such as Frederick Law Olmsted transformed cities with their natural park designs. With green spaces, squirrels could get a pawhold.
One of my daughter’s favorite repeat YouTube videos is this guy who set up a squirrel obstacle course in his back yard. He has four regular squirrels that show up that he names and tracks. (It’s more interesting than I make it sound.)