Cambridge, Mass.
1910.
Feb. 6 [February 6, 1910]
  Clear and cold with fresh N. W. [Northwest] wind.
  During the past two or three weeks the Gray Squirrels
on our place have been acting as if this rutting season had
begun or was close at hand. I have frequently seen them
toying with one another in the trees in a suggestive way
(this they do more or less at all seasons, however) and twice
or thrice have watched a protracted chase in which two
or three took part and which was conducted chiefly over
the snow-covered surface of the ground, the leading animal
keeping a yard or two in advance of her pursuer or
pursuers and running at top speed for several minutes
at a time, during which almost every part of the
garden was traversed. All this has hitherto ended in
nothing definite, as far as I could observe; but early
this morning I saw the act of copulation performed,
probably at the termination of a rather long pursuit.
Rutting
season of 
Gray Squirrels