I just discovered all of the nesting material has been removed from two bird houses where industrious house sparrows have been working for the past few days. The houses are mounted on 2x2 posts about 6 feet tall, supported against a 4 foot tall chain link fence. I'm blaming the squirrels since I saw one bothering the tenants of another bird house, but it could possibly have been a racoon I suppose. Any suggestions for keeping pests away from bird houses?

Jan