From your description, a flying squirrel might not be big enough, but in any case:

According to this page (http://www.wellsreserve.org/news/2004-09-07_squirrel.htm):
"Maine is home to two species of flying squirrel, both of which are more common than you might think. Flying squirrels are about the size of a chipmunk, but are creatures of the night."

http://www.mainenature.org/ has an article on Flying squirrels in the Quoddy region, and mentions seeing them eating birdseed.