Squirrel network

My second ongoing project involves--you guessed it--squirrels. I've formalized what I've been informally tracking for a while now: which areas have eastern fox squirrels, eastern gray squirrels or both. I received an e-mail from a correspondent mentioning that gray squirrels are prevalent in St. Paul, Minn. I now have information on 13 localities regarding the fox vs. gray conundrum. (Limited to eastern North America since these squirrels largely reside--and overlap--here.) A few areas, such as Southeast Michigan enjoy the great squirrel triumvirate of fox squirrel, gray squirrel and red squirrel. Wow.

Still, it's not really clear why grays dominate some areas and foxes in others. "A Field Guide to Mammals" suggests that fox squirrels reside in wooded areas with large clearings and gray squirrels in hardwood forests and river bottoms. Neither description accounts for the urban and suburban squirrels. One of my early conclusions is that only gray squirrels live in intensely urban areas. If I'm wrong, let me know. Further input from other areas would be much appreciated. The fox squirrel, right, can be distinguished from the gray squirrel by its larger size (like a small house cat) and golden-tinged tail and underparts.