A couple of Eastern Grey Squirrels tucked into this tree. One had a mouthful of dry leaves, new insulation. Unlike in local parks, Green-Wood’s squirrels are fairly shy. (No picnickers to provide food; no European tourists to be rolled.)
And then there’s….
Two skulls found under a pine that hosted a Red-tailed Hawk nest last spring. These actually seem to be Brown Rat rather than Gray Squirrel, but the idea is the same: rodents beware!
On the other paw, climbing up a Poison Ivy festooned stump?
No big deal!
You never know what will turn up under a Yew. It has been suggested this is a domestic cat skull.
Backyard and Beyond 
Nice photos and descriptions!