When we first moved in, we noticed what seemed to us to be chipmunks in the line of Norway spruce and hemlocks along the back of our yard. In Austin, we were at the western edge of many species, including the fox squirrel, which has a black variety common on the Texas Capitol lawn. Our back yard was full of fox squirrels, which even bigger than the grey squirrel I grew up with, and the ones in our evergreens seemed tiny. As it turns out, they are red squirrels. I had probably never noticed them growing up because they eat evergreen seeds, and we didn’t have many in town.
I wondered if our red squirrels were the same as the ones being driven out in England by imported North American gray squirrels. They are a different species, more closely related to our gray and fox squirrels than to our little red squirrel.
The Smithsonian has a great on-line field guide to mammals. One feature allows you to choose a location and create a custom printable PDF field guide of just the mammals for that area.