Any time that birds congregate in large groups to share food and water sources, there is the potential for disease transmission and disease outbreaks. Thus, cleaning your bird feeders on a regular basis is an important part of being a good steward to the birds.
Salmonellosis is the most common infectious disease in wild birds, caused by the Salmonella bacteria. Symptoms include lesions in the digestive tract, lethargy, diarrhea, loss of coordination, and death.
Mycoplasmosis, caused by the Mycoplasma bacteria, is another bacteria commonly found in birdfeeders and easily transmitted between individuals at shared food sources. Mycoplasmosis can cause crusty and swollen eyes leading to reduced vision and an increased risk of starvation and predation.
Researchers in Pennsylvania tested the effectiveness of three different cleaning methods in removing the Salmonella bacteria from hopper-style bird feeders; 1. scrubbing with soap and water, 2. soaking in a bleach solution, and 3. a combination of both. They found that cleaning methods involving bleach were significantly better than soap and water alone at reducing the level of Salmonella present in bird feeders. This is especially true if there is debris remaining in the bird feeder, such as feathers or uneaten seed. Researchers found that soap and water alone are not effective at reducing the level of Salmonella to below pathogenic levels when debris is present. Researchers in a separate study found that, as debris accumulates over time, even the efficacy of cleaning with a bleach solution begins to diminish.
The best way to ensure that you are providing a safe and healthy food source for wild birds is to prevent the build-up of debris on your feeders by cleaning them often and thoroughly.
The frequency at which birds visit your feeder may change throughout the year, so use your best judgement when deciding how often you clean your feeders. For instance, during peak spring or fall migration, you may have hundreds of birds visiting your bird feeders each week, so daily cleaning is advised to ensure that bacteria does not have a chance to grow on any remaining debris.
The information above was summarized from Feliciano, L. M. et al. 2018
Feliciano, L. M., Underwood, T. J., Aruscavage, D. F. 2018. The effectiveness of bird feeder cleaning methods with and without debris. The Wilson Journal of Ornithology. 130(1): 313-320.