Understanding Backyard Bird Diseases: A Comprehensive Guide

Beyond vibrant plumages, a silent threat may lurk among our backyard feathery friends: Backyard Bird Diseases. While headlines often focus on large and popular  birds a quieter worry floats among folks that feed birds in their backyards: are our beloved songbirds next? 

This comprehensive guide delves into the complex world of backyard bird diseases, providing you with the knowledge to protect our birds and ourselves. From understanding transmission pathways to identifying common infections, I unlock the secrets of keeping your backyard a place healthy for birds. 

While bird diseases have similar the ruffled feathers and position shown in this picture is typical of most bird diseases. Photo: Andrea Lahue.

Fundamentals of backyard bird  diseases

What is bird disease?

The term “bird disease” refers to a variety of health conditions that can affect backyard birds and other birds, including infectious and non-infectious diseases. These diseases can cause significant mortality in birds and can have a major impact on the health of wild bird populations.

Common backyard bird diseases

This is a list of only common backyard bird diseases. The prevalence of these diseases can vary significantly based on location and specific bird populations. 

It’s always best to consult with a local wildlife rehabilitator or veterinarian for specific concerns about sick birds in your area.The following are common bacterial, viral, and parasitic diseases:


  • Salmonellosis: This bacterial infection causes diarrhea, lethargy, and ruffled feathers. It can spread through contaminated food and water sources at feeders.
  • House Finch Eye Disease: Caused by a bacteria-like organism, this disease affects the eyes and respiratory system, leading to conjunctivitis, runny eyes, and difficulty breathing.
  • Avian Chlamydiosis: This bacterial disease affects respiratory and reproductive systems, causing labored breathing, nasal discharge, and eye problems.


  • Avian Pox: This viral disease creates wart-like lesions on the beak, legs, and eyes. While not usually fatal, it can weaken birds and make them susceptible to other infections.
  • Avian Influenza: A global flu virus with the potential to sicken both birds and humans. While primarily affecting poultry and waterfowl, it can sometimes jump to songbirds.
  • West Nile Virus: This mosquito-borne virus can cause neurological problems and death in some birds. While not a common threat to backyard birds, it’s important to be aware of it.


  • Bird Mites: These tiny external parasites can cause itching, feather loss, and skin irritation. They can also spread other diseases.
  • Feather Lice: These chewing lice feed on feathers and skin debris, causing irritation and discomfort. Heavy infestations can lead to feather loss and even death.

Other Diseases

  • Trichomoniasis: This protozoan parasite affects the upper digestive tract, causing difficulty swallowing and weight loss.
  • Worms: From harmless freeloaders to potential health hazards. Worms are common bird parasites and can sometimes cause trouble for backyard birds.
  • Aspergillosis: A stealthy fungus lurking in the air. Though ever-present, Aspergillosis only strikes vulnerable birds, causing subtle respiratory woes like gasping breaths and ruffled feathers.

Nutritional Deficiencies

  • Vitamin A Deficiency: This can occur when birds rely solely on seeds for food, leading to lethargy, poor feather quality, and weakened immune systems.

What causes bird diseases in backyard birds?

Although it is often difficult to manage, bird feeder overcrowding may lead to transmission of disease in backyard birds. Pine Siskins. Photo: Kate Ter Harr.

Several factors can contribute to the spread of disease in backyard birds, and they can be categorized into direct and indirect causes:

Direct Causes

  • Contaminated food and water sources: Dirty feeders, stagnant water features, and moldy birdseed can harbor bacteria, viruses, and parasites that birds can easily ingest.
  • Contact with other infected birds: Crowded feeders, bird baths, and nesting sites can increase the chances of transmission through direct contact or airborne pathogens.
  • Stressful environments: Competition for resources, lack of suitable cover, and exposure to predators can weaken a bird’s immune system, making them more susceptible to illness.
  • Human-related activities: Introducing non-native bird species or neglecting proper hygiene practices can disturb the natural balance and introduce new pathogens.

Indirect Causes

  • Habitat loss and fragmentation: Reduced availability of natural food sources and nesting sites can force birds into closer contact with each other and potentially contaminated areas.
  • Climate change: Shifts in temperature and precipitation patterns can alter the distribution of disease-carrying vectors like mosquitoes and ticks.
  • Use of pesticides and herbicides: These chemicals can disrupt the natural balance of the ecosystem and harm beneficial insects that help control disease outbreaks.

How are diseases transmitted among backyard birds?

A problem with baths is that bird often deposit dropping in them leading to the transmission of pathogens. American Robin. Photo: Jo Zimny.

Diseases among backyard birds can spread through several different mechanisms, some of which are more common in backyard settings than others. Here’s a breakdown of the key transmission mechanisms:

1. Direct Contact

  • Beak-to-beak contact: This can happen during feeding, mating, or even aggressive interactions. Viruses, bacteria, and parasites can easily pass from one bird to another through this close contact.
  • Feather contact: As birds preen and groom themselves, feathers can transfer pathogens to other birds. This is especially common with parasites like lice and mites, which can cling to feathers and move between birds.
  • Touching of droppings or bird poop: This occurs when a bird’s droppings touch another bird, either directly or through contaminated surfaces. Bacteria and parasites are common culprits in this type of transmission.

2. Indirect Contact

  • Contaminated food and water: Dirty feeders, stagnant water features, and moldy bird seed can harbor pathogens that birds can ingest. This is a major source of bacterial and parasitic infections in backyard settings.
  • Environmental contamination: Bird poop (droppings), feathers, and other debris can contaminate surfaces like bird baths, nesting boxes, and even the ground. This creates a reservoir for pathogens that can be picked up by other birds.
  • Aerosols: In some cases, viruses and bacteria can be transmitted through the air, especially in crowded conditions or when birds are stressed. This is less common in backyard settings but can still occur.

3. Vector-borne transmission

  • Mosquitoes: These insects can transmit diseases like West Nile virus and avian malaria to birds. Mosquitoes breed in stagnant water, so keeping birdbaths clean and fresh is important for preventing this type of transmission.
  • Ticks: Ticks can transmit diseases like Lyme disease and avian borreliosis. Ticks are more common in wooded areas, so avoiding placing feeders in shady areas can help reduce the risk.

How prevalent bird diseases are in backyards

While most birds are susceptible to most bird diseases, some species such as House Finches appear to be most susceptible to mycoplasmal conjunctivitis (House Finch Disease).

Backyard bird diseases are fairly common and can affect a wide variety of bird species. I found a study conducted by the Cornell Lab of Ornithology in Ithaca, New York, where they identify five of the most common backyard bird diseases. These include: 

  • House finch eye disease
  • Avian pox
  • Salmonellosis
  • Trichomoniasis and 
  • Aspergillosis

It is important for backyard birders to be aware of the signs of these diseases in order to help prevent their spread. Some common signs of bird diseases include:

  • Lethargy
  • Loss of appetite
  • Difficulty breathing 
  • Discharge from the eyes or beak, and
  • Changes in behavior or appearance.

While backyard bird diseases can be concerning, it is important to note that not all birds will be affected and there are steps that can be taken to help prevent the spread of disease. 

Learn more about Whether or Not We Should Feed Backyard Birds.

Identifying and diagnosing common backyard bird diseases

Observation and note taking of the appearance and behavior of birds in your backyard may lead to rapid detection and reaction to bird diseases.

Identifying and diagnosing common backyard bird diseases can be challenging, especially without veterinary expertise. However, observing changes in bird appearance, behavior, and feeding patterns can offer valuable clues. 

Remember, early detection and intervention can significantly improve a bird’s chances of recovery. Here are some common backyard bird diseases and their tell-tale signs:

1. Avian Pox:

  • Symptoms: Wart-like lesions on beak, legs, and eyes, sometimes accompanied by drooping wings and lethargy.
  • Appearance: Lesions may be red, gray, or brown and crusty.
  • Behavior: Difficulty eating, decreased activity, and avoidance of other birds.

2. House Finch Disease:

  • Symptoms: Red, swollen, runny, or crusty eyes, conjunctivitis, and difficulty breathing.
  • Appearance: Crusted eyelids may obscure vision.
  • Behavior: Difficulty feeding, lethargy, and fluffed feathers.

3. Trichomoniasis:

  • Symptoms: Difficulty swallowing, weight loss, drooling, and regurgitation.
  • Appearance: Birds may appear emaciated and weak.
  • Behavior: Decreased activity, and reluctance to fly.

4. Salmonellosis:

  • Symptoms: Diarrhea, lethargy, ruffled feathers, and loss of appetite.
  • Appearance: Birds may appear dehydrated and weak.
  • Behavior: Decreased activity, isolation from other birds, and frequent droppings near feeders.

5. Avian Influenza:

  • Symptoms: Difficulty breathing, coughing, sneezing, and diarrhea.
  • Appearance: Birds may appear lethargic and have ruffled feathers.
  • Behavior: Decreased activity, loss of appetite, and isolation from other birds.

Additional Tips for Identification:

  • Pay attention to changes in vocalizations: Sick birds may chirp less frequently or make unusual sounds.
  • Observe droppings: Changes in color, consistency, or frequency of bird poop can indicate illness.
  • Look for abnormal movements: Difficulty flying, perching, or walking can be signs of weakness.
  • Monitor interactions with other birds: Sick birds may be ostracized or avoided by healthy birds.

This list is not exhaustive, and symptoms can vary depending on the specific disease and the individual bird. It’s always better to err on the side of caution and seek professional help if you suspect a bird is sick. By acting quickly and responsibly, you can help ensure the health and well-being of your backyard birds.

How does disease impact my backyard birds? 

Diseases can have a significant impact on your backyard birds, affecting their health, behavior, and overall well-being in various ways. Here’s a breakdown of the potential consequences:

Physical Health:

  • Reduced immunity: Diseases can weaken a bird’s immune system, making them more susceptible to other infections and parasites.
  • Organ damage: Some diseases can damage vital organs like the lungs, liver, and kidneys, leading to organ failure and death.
  • Malnutrition: Difficulty eating or absorbing nutrients due to illness can lead to weight loss, weakness, and even starvation.


  • Lethargy and decreased activity: Sick birds often conserve energy and become less active than usual.
  • Changes in feeding patterns: Reduced appetite, difficulty swallowing, or avoiding feeders can be signs of illness.
  • Abnormal movements and vocalizations: Difficulty flying, perching, or walking, and changes in vocalizations like chirping less frequently or making unusual sounds can be indicators of weakness or pain.

Population Health:

  • Disease outbreaks: In severe cases, diseases can spread through bird populations at feeders, nesting sites, or other points of contact, leading to significant mortality.
  • Habitat disruption: Sick birds may abandon nests, avoid preferred food sources, and generally disrupt the natural balance of the backyard ecosystem.

Disease outbreaks can also impact you, the backyard birder. Sick birds can result in reduced bird sightings and activity in your backyard. Seeing sick birds can also cause emotional distress.

Although very rare sick birds can potentially transmit diseases to humans.

What can I do to keep my backyard bird feeding station free from disease?

Practicing proper hygiene and changing of water in drinking or bath tubs help minimize the spread of disease. Photo: Migchigan DNR.

Maintaining a clean and healthy feeding environment is an ongoing process. Consistent effort and vigilance will help you keep your backyard birds happy and healthy for years to come.

The following tips are intended to help you create a healthy, diverse backyard habitat that significantly reduces the risk of disease at your bird feeding station and enjoy the company of healthy and thriving birds.

Hygiene and Maintenance:

  • Clean your feeders regularly: Do this at least twice a week, especially during warm weather. Disassemble the feeder and scrub all parts with hot soapy water, followed by a 10% bleach solution (1 part bleach to 9 parts water). Rinse thoroughly and let air dry completely before refilling.
  • Replace worn-out feeders: Cracked or damaged feeders harbor bacteria and encourage mold growth. Opt for feeders made of easy-to-clean materials like stainless steel or ceramic.
  • Provide fresh, clean water: Clean and refill bird baths regularly, removing any algae or debris. Consider using a circulating birdbath with a filter to prevent stagnant water.
  • Move feeders regularly: This may be difficult but it helps prevent the accumulation of droppings and food waste under the feeder, reducing the risk of contamination. Alternatively, maintain the area under the feeders free from food waste accumulation. 

Food and Habitat Management:

  • Offer a variety of healthy foods: Don’t rely solely on birdseed. Supplement with fruits, nuts, suet, and other natural foods to provide a balanced diet and boost bird immunity.
  • Rotate your food sources: Avoid offering the same food for extended periods. This can attract birds with specific diseases and encourage them to linger, increasing the risk of transmission.
  • Manage spills and debris: Promptly remove any spilled food or debris from under the feeder to prevent attracting pests like rodents and insects, which can carry diseases.
  • Plant native vegetation: This attracts a wider variety of birds and provides them with natural food sources, reducing reliance on feeders and potentially reducing disease transmission.

Bird Observation and Community

  • Monitor bird behavior: Pay attention to changes in bird activity, feeding patterns, or appearance (e.g., ruffled feathers, lethargy). If you suspect a bird is sick, remove it from the feeder and contact a wildlife rehabilitator or veterinarian.
  • Discourage overcrowding: Use multiple feeders spaced apart to avoid competition and crowding, which can facilitate disease transmission.
  • Educate other backyard birders: Share your knowledge about hygiene and disease prevention practices with other bird enthusiasts in your area.
  • Consider using bird-friendly disinfectants: Some commercially available disinfectants are specifically formulated for bird feeders and are less harmful to birds and the environment than bleach.

What should I do if my backyard birds become infected with a disease?

If your backyard birds become infected with a disease, here are some actionable tips to help:

Immediate Steps

  1. Isolate sick birds: This prevents the spread of disease to other healthy birds. Remove sick or dead birds from feeders, birdbaths, and other feeding areas. 
  2. Stop feeding: Discontinue using your feeders for at least two weeks to discourage further gathering and potential transmission. This also gives you time to thoroughly clean and disinfect your feeders.
  3. Clean and disinfect feeders and birdbaths: Follow these steps:
    • Disassemble feeders: Take apart all removable parts.
    • Wash thoroughly: Scrub all surfaces with hot soapy water.
    • Disinfect: Use a 10% bleach solution (1 part bleach to 9 parts water) or a commercially available bird-friendly disinfectant. Rinse well and air dry completely.
    • Clean birdbaths: Empty and scrub the surfaces with hot soapy water. Rinse thoroughly and let dry completely.

Monitoring and Reporting

  1. Observe sick birds: Watch for changes in behavior, appearance (e.g., ruffled feathers, lethargy), and feeding patterns. Take note of any specific symptoms to help with diagnosis.
  2. Contact a wildlife rehabilitator or veterinarian: They can diagnose the disease and provide guidance on treatment options, if possible. Be prepared to describe the symptoms and your efforts to contain the spread.
  3. Report the outbreak: Notify your local wildlife agency or birdwatching organization. This helps them track disease patterns and potentially implement broader control measures.

Do not attempt to treat sick birds yourself. This can worsen their condition and potentially expose you to pathogens.

Monitoring the activity at your feeders and quick reaction help minimize the spread of backyard bird diseases.

How should one handle a bird that appears to be diseased?

If you come across a bird that appears to be sick or diseased, it is best to avoid handling or touching it. Sick birds can be carriers of various diseases that can be transmitted to humans through direct contact, inhalation, or ingestion of contaminated materials. 

Instead, you should contact your local wildlife rehabilitation center or a licensed wildlife rehabilitator for guidance on how to handle the situation.

Which of the common backyard bird diseases are transmissible to humans?

It’s important to first understand that while some bird diseases can theoretically be transmitted to humans, the risk is generally low for most healthy individuals practicing good hygiene habits.

Here’s a breakdown of some common backyard bird diseases and their potential transmission to humans:

Diseases with low risk of transmission to humans:

  • Avian Pox: While the virus can infect humans, it’s extremely rare and requires direct contact with infected bird lesions, which is unlikely, unless the bird is dead.
  • Salmonellosis: Transmission mainly occurs through contaminated food or water sources. Practicing good hygiene and ensuring bird feeders are clean and well-maintained significantly reduces the risk.
  • House Finch Disease: This bacterial disease hasn’t been documented to transmit to humans, but it’s still best to avoid contact with sick birds and maintain clean feeders.

Diseases requiring extra caution:

  • West Nile Virus: While primarily spread by mosquitoes, it’s theoretically possible for humans to contract it through contact with infected bird droppings (poop) or carcasses. Avoiding direct contact and wearing gloves if necessary while cleaning feeders or bird baths is recommended.
  • Trichomoniasis: This parasite can theoretically infect humans through contaminated water sources, but the risk is very low for healthy individuals. Maintaining clean birdbaths and avoiding prolonged exposure to contaminated water is advisable.

General Tips for backyard bird feeding:

  • Avoid direct contact with sick birds or their droppings.
  • Maintain clean feeders and birdbaths regularly.
  • Wash your hands thoroughly with soap and water after handling bird feeders or birdbaths.
  • Avoid attracting rodents or other pests that can spread disease.
  • If you suspect a bird is sick, contact a wildlife rehabilitator or veterinarian.

Also see: What to do upon Encountering Sick Birds.


Kilpatrick, A. M. (2011). Globalization, land use, and the invasion of West Nile virus. Science, 334(6054), 323-327. https://science.sciencemag.org/content/334/6054/323

Prosser, D. J., Hungerford, L. L., Erwin, R. M., Ottinger, M. A., & Takekawa, J. Y. (2011). Avian influenza viruses in wild birds: A moving target. Comparative Immunology, Microbiology and Infectious Diseases, 34(4), 325-332. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3079983/