If you want to keep your feeder defrosted like one of the pros, go to
the local plumbing supply store. Not Lowes or Home Depot, they will only give you a blank stare. Here in Bend try Searing's on N.E. 2nd street. Invest the $8-10 for a clamp-on light fixture that looks like this (photo here).
Plug in a 125 Watt Infra-red light bulb, but don't get the red-glass type. Get an I.R. bulb with clear envelope, it casts a more natural light. Hang it using the adjustable, integrated clamp so it points at the feeder from one or two feet away. This is the way plumbers defrost frozen pipes. I plug mine up to a timer so it comes on an hour before sunrise and clicks off an hour after sunset.
1 day ago