This beat-up skull comes courtesy of a Great Horned Owl. The owl chomped this down and then spit it back up after the bird’s battery acid stomach had a go at it. 
I think these might be the remains of a Grey Squirrel skull. 
Found with plenty of grey hair smushed into the cavities. Cleaned up a bit with toothpick and hydrogen peroxide, but it was already virtually bleached by the owl. 
Check out these incisors and molars.
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Forty-nine years since the first Earth Day. Here are forty years of measurable transformations in migrating birds: a new study finds warmer temperatures are decreasing body size and increasing wing length.
Backyard and Beyond 
nice blog post as always keep it up
Squirrel?
I think so. Missing the backend, eye sockets, etc.
Interesting study on changes in bird morphology.