Birds live outdoors among all manner of dirt, bugs and weather, so why, you might argue, would a soiled birdfeeder be of any concern, as long as it’s filled with the things birds eat?
I found out there’s plenty of good cause to keep your feeders clean.
Birdseed that becomes damp or rotten harbors bacteria and disease that can quickly spread throughout a flock, decimating a local population. Also, rancid seed smells bad, which attracts predators such as raccoons and rats that not only present a danger and nuisance, but that can also carry disease.
Feeders should be cleaned once a month in dry weather and once every few weeks in warm, damp weather. Bird food high in fat content, such as suet, is even more prone to turning rancid. For best results, take apart the pieces of the feeder and scrub with a bottle brush thoroughly with dish soap, or a solution of one part bleach and nine parts water. Rinse well and allow the feeder to dry thoroughly. Hummingbird feeders should be cleaned with each refill. Plastic feeders can usually be safely cleaned in the top rack of a dishwasher.
Take care, as well, to remove piles of old seed or husks from around the base of the feeder, where bacteria can also grow. Refresh mulch or gravel under feeders periodically to cover bird feces.