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Avian Influenza
Avian Influenza
CPW biologist necropsying a goose

​​​​​​​​​​​​Avian influenza​​

Avian influenza is an infectious disease of birds caused by a group of influenza A viruses. These viruses naturally circu­late in wild waterfowl and shorebirds, which typically carry the viruses without showing any signs of disease. Most of these avian influenza viruses are considered low-pathogenic (LPAI) strains that cause little or no clinical signs in any species. However, LPAI strains may naturally mutate into strains that do cause severe disease in birds (and sometimes other species). These disease-causing strains are the highly pathogenic (HPAI) strains that have caused severe disease and high mortality in birds, especially domestic poultry.​

New HPAI Strain in 2021-2022

In the winter and spring of 2021-2022, an outbreak of Highly Pathogenic Avian Influenza (HPAI) involving a new strain of H5N1 emerged in North America. Unlike prior strains of HPAI in North America, this particular strain is causing widespread mortality in some species of wild birds, particularly in snow geese, raptors, and vultures. This strain has also caused mortality in several mammal species, especially in skunks and foxes. For more information on HPAI in mammals, please visit the U.S. Department of Agriculture (USDA)​ website​.

Early Colorado Cases

This strain of HPAI was first confirmed in wild geese in Northeast Colorado in March of 2022. From March through November 2022, HPAI mortalities were documented in a number of raptors, waterfowl, and vultures in numerous locations throughout the state. Most reports were of limited mortalities involving individual birds or small numbers of birds and there was one mortality in a striped skunk. All confirmed HPAI cases in Colorado (both domestic and wild) can be viewed on maps available at the Colorado Department of Agriculture website.

November 2022

In late November 2022, Colorado Parks and Wildlife (CPW) began receiving increasing reports of sick and dead snow geese in Northeastern Colorado associated with large-scale HPAI mortality events. CPW personnel documented mortalities in excess of 1,000 birds on multiple waterways in Morgan and Logan Counties. Shortly thereafter, large-scale mortalities began occurring in southeast Colorado in Kiowa, Bent, Otero, and Prowers counties. Total snow geese mortality numbers are unknown, but mortality reports range from a single animal to more than 1,000 dead geese on a single reservoir. These mortality events coincide with fall migrations of birds leading to large congregations of snow geese in Colorado.

At the national level, outbreaks in wild birds and poultry continue to rise and the U.S. is approaching a record number of birds affected compared to previous bird flu outbreaks. To date, HPAI has been detected in all four North American migration flyways. It is expected that the disease will persist through spring migrations. 

Coordinated Multi-Agency Effort

Concern for HPAI in wild birds, domestic poultry, humans, and the environment overlaps multiple state and federal agencies. Colorado Parks and Wildlife is coordinating with the Colorado Division of Homeland Security and Emergency Management, Colorado Department of Agriculture (CDA), United States Department of Agriculture (USDA), and Colorado Department of Public Health and Environment (CDPHE) to share available data and coordinate response plans. ​

Frequently Asked Questions

Can humans get this strain of HPAI?

Although rare, some HPAI strains can infect people. The human health risks from this strain of HPAI is low according to the Centers for Disease Control and Prevention (CDC). CPW recommends that people avoid handling dead or sick birds or other animals. Precautionary measures such as personal protective equipment (PPE) are recommended for people who may have job-related or recreational exposures to birds that can put them at higher risk of infection. Visit the CDC website for more information on protective actions for people.

Does Avian Influenza cause disease in wild birds?

Most wild birds infected with avian influenza virus do not show signs of disease. However, the 2022 strain does cause disease in some wildlife species including swans, gulls, geese, grebes, pelicans, raptors, vultures, cranes, and some species of ducks. In these birds, typical symptoms include swimming in circles, moving slowly, incoordination (may appear drunk), and head tilt or inability to lift the head. Most affected birds are seen on the ground, but occasionally sick birds may be seen flying low and alone. Game bird species such as turkeys, grouse, and quail may also be susceptible to HPAI.

What to do if you find sick or dead birds?

If you find three or more dead wild birds in a specific area within a two week period OR if you see live birds showing clinical signs of disease, please contact your local Colorado Parks and Wildlife office. Please be aware that CPW will not be able to respond to all calls and is focusing responses based on surveillance and management priorities.

As a general guideline, members of the public should avoid handling sick or dead birds. If you do need to dispose of an individual or limited number of bird carcasses on your private property, wear a mask, eye protection (such as sunglasses), and gloves to pick up the carcass. Carcasses should be immediately double bagged and placed in municipal trash. Discard gloves and mask and wash your hands immediately afterwards.

How does CPW conduct HPAI surveillance?

CPW is currently focusing surveillance by species, county and season. Once HPAI has been confirmed in a certain species and county, we will not test additional birds of that species within that county until the next season. We still appreciate reports of sick and dying birds to help inform us of the extent of an event, but we do not need to test every sick or dead bird.

How are birds tested for HPAI?

Sick or dead birds that are identified for surveillance may be tested in two ways. CPW personnel may collect swabs from the bird or collect the entire carcass. Whole carcasses are necropsied by the CPW wildlife pathologist to determine cause of death, record additional information about the bird, and collect additional samples for testing. Any HPAI samples are then submitted to the Colorado State University Veterinary Diagnostic Laboratory. Positive HPAI results are confirmed by the USDA National Veterinary Services Laboratories.

Can birds with HPAI be rehabilitated?

Rehabilitation of wild birds with this strain of HPAI is challenging and most birds that become sick will die. Members of the public are welcome to contact a wildlife rehabilitator to determine whether a bird is a candidate for rehabilitation. Do not attempt to pick up or handle sick birds. If a rehabilitator is able to take a bird, they will work with you to arrange safe pick up and transport of the bird.

Can I still hunt waterfowl during this outbreak?

Healthy flying waterfowl are unlikely to pose a significant risk to hunters. To date, there are no reports of people becoming infected with this strain of avian influenza directly from wild birds. Hunters are advised to avoid harvesting birds that appear sick. Most birds that are sick with HPAI will be on the ground; however, in some cases, sick snow geese may be seen flying very low and alone. Below are some basic precautions that hunters should always take when handling and consuming wild game:

  • Do not handle or eat wildlife found sick or dead.
  • Do not eat, drink, smoke, or put anything in your mouth while cleaning or handling game.
  • Wear rubber or latex gloves when handling and cleaning game.
  • Wash hands thoroughly and disinfect knives, equipment, and surfaces that come into contact with game.
  • Keep wild bird carcasses away from domestic poultry
  • Cook all game thoroughly to an internal temperature of 165°F

Should I be worried about my dog or cat becoming infected with HPAI?

Certain mammals—including domestic cats and dogs—may become infected if they eat sick or dead infected birds or are exposed to an environment contaminated with avian influenza virus. According to the American Veterinary Medical Association, the likelihood of cats and dogs catching HPAI seems low. For more information, please visit the American Veterinary Medical Associations website.

If your dog or cat is showing signs of illness, then please contact your veterinarian for further evaluation. Visit the CDC's website for more information on HPAI in pets

What is the impact of this disease on Colorado’s wild birds?

Previous HPAI strains had minimal impact on wild bird populations. Avian influenza is common in wild birds, particularly in waterfowl and other waterbirds, and these species are reservoirs for the disease. The current strain appears to be impacting wild birds across North America, producing relatively large (or at least more noticeable) die-offs in wild birds, and affecting a relatively large variety of wild bird species. Impacts from the current HPAI strain are unknown at this time. Snow goose and most other waterfowl populations are currently robust and most species can likely tolerate relatively high losses this winter without impacting population viability, but it is unclear whether long-term or sustained losses would impact overall abundance or population trends over time. The more immediate concern is the potential impact on raptors. Raptors are particularly susceptible to this strain of HPAI and we are seeing many mortalities in hawks, owls, and eagles. There is potential for effects on numbers and distribution of some raptor species at local and regional scales.

Will the large number of carcasses affect water quality or drinking water?

Colorado Parks and Wildlife is coordinating with the Colorado Department of Public Health and the Environment to share information and coordinate response plans. All drinking water from public reservoirs is treated to ensure it is safe for people to drink.

Will a large number of carcasses affect our aquatic ecosystems?

Low numbers of dead birds (less than 100) pose little risk to most aquatic systems, especially larger bodies of water. Animals often perish and decompose in lakes with no ill effect on the water quality or fishery. When large numbers (hundreds or thousands) of dead birds are present, the decaying process can add significant amounts of nutrients to the system, causing a variety of water-quality issues including large-scale algae blooms. Algae blooms can result in lower dissolved oxygen conditions leading to fish kills. This is a greater concern in static systems with no fresh inflow or outflow such as Nee Noshe, Nee Gronda, and Adobe Creek Reservoirs. The decomposition process can also result in what appears to be an oil sheen on the water and has often been mistaken for a petroleum or chemical spill.

Dead birds that wash up on shore or are carried up on shore by scavengers are less of a concern than the birds that die, become waterlogged, and sink to the bottom. Aquatic scavengers such as catfish and crayfish can be effective at removing small amounts of carrion from the local aquatic system.

Additional Avian influenza Resources

Additional information on avian influenza can be found at the following: