Is there a good substitute for bleach when disinfecting wild bird feeders and nesting boxes?
If you don't want to use bleach to disinfect your feeders or nesting boxes, plain white vinegar is a great alternative. A 5-percent vinegar solution kills the majority of bacteria, viruses and molds. Tea tree oil is also an effective disinfectant — you can find it at most health food stores. Simply mix a teaspoon of the oil in a gallon of warm water and scrub away.
— David Mizejewski, naturalist, National Wildlife Federation