Bird Feeders should be cleaned at least once a month to keep your birds healthy and maintain there regular visits to your feeders. When it rains, the water may sneak it's way into your feeder, creating and incubating mold and other bacteria in the feeder, a great way to get rid of this problem is making sure all your bird seed is removed from the feeder, if you do notice mold on the seed, please throw it all away. Once your feeder is free of the seed, soak your feeder in a solution of 1 tbsp of Bleach to one gallon of water for about 10-30min. After your feeder has finished soaking, rinse your feeder out with clean water, making sure you have removed the bleach and the mold. After completing that, your feeder should be ready to be put back up and have your seed back in. Remember to follow these steps at least once a month, especially in the summer.