What Species of Bird is This?

This big, fat 'bird' is quite a bit heftier than the little junco that dined here recently. With the winter weather coming on now in earnest, there has been increasing activity around the bird feeder, including juncos, jays, and this hungry and agile squirrel.

Though this food is meant for the birds, I really don't mind this fellow joining in, there's plenty of seed for all hungry visitors!

Mmmm, sunflower seeds!