Recleaned Cracked corn - the idea that corn is a filler is false. In smaller quantities in mixed seed its very appropriate and the larger birds will love it. On its own its a great way to distract squirrels to their own feeder and leave your more expensive birdseed alone. 

Birdhouse Tip: Things like wheat and oats and milo are fillers and will either be tossed to the ground and not eaten, or can potentially attract unwanted animals and birds.