Isn't the first robin or a snowdrop.
It is the male squirrel and the start of nest expansion. The fools are
running across the roof, jumping off a branch onto the roof or jumping off
the roof with yet another twig to expand those nests. Any thing to avoid the
feral cat that has claimed the yard as her territory.
Most years, I only hear one or two during nest building. This year it is one
or two an hour. Thump, skitter, skitter, skitter, plop. Off the pine or oak,
onto the roof, across the length of the house and down again. Now and again,
one of them can't stay on (I have a steep pitch) and down he slides and
hangs on to the eave like a gymnast before hauling himself back up or
dropping 20 feet to the ground.
A visual definition of squirrelly.