Black Squirrels are as common as muck around here. I rarely see a grey squirrel and am even less likely to see a red squirrel. I happened to look out of the patio door and saw a squirrel sun bathing in the afternoon sun on the fence on Friday.
I find black squirrels quite aggressive when it comes to the bird feeders. They want what they want, and they want it now! As our neighbour has numerous bird feeders out, squirrels are around a lot.
I was reading on the Squirrels at the Feeder site, that black squirrels are better adapted for the cold and will become the dominant species in northern climates. That site is worth checking out by the way if you are interested in squirrels; lots of interesting facts there.

