I have several bluebird nesting boxes around our yard. Every fall I go through and clean them out. Years ago I read how important it is to clean them out in the fall so the old nesting material doesn't attract bugs. Hubby and I were discussing this and he thought it would be best to wait until spring to clean them out. His theory was the birds may need the nesting material for winter warmth. And to wait until spring to clean out the nesting boxes. Thought I'd see what everyone else does/has to say on this topic. My yard is registered with the Wildlife Federation, maybe they will have an answer to this question as well.