Stumpy

For some time now we have occasionally caught a glimpse of a creature scurrying about in the undergrowth at the far side of the Trentham Lake.  It was rat-like, or perhaps a small rabbit, fast and well hidden in the ground cover, not seen in any detail, just a glimpse and a doubt about what was seen.

We now know it is a squirrel with a stumpy tail.  It has difficulty balancing when it jumps or climbs, so it is restricted to un-squirrel-like behaviour.
The question that is now begging an answer -  Is the short tail a genetic trait or an injury?  It does not look abnormally damaged in any of the photographs I have taken.  If it is a genetic mutation, are there other squirrels like this one?
This short tail certainly changes the ability of the animal to climb trees, making it more adapted to foraging in ground cover vegetation.  This animal has probably been around for several years and it seems comfortable with its habitat restrictions, looking very healthy and well fed.