Avian botulism, probably the most well known of waterfowl diseases, results from the ingestion of a toxin produced by the bacterium Clostridium botulinum. This disease attacks the nervous system and can result in death in as little as 24 hours. Major avian botulism epizootics have been reported throughout North America for more than a century. In 1910, avian botulism resulted in the deaths of millions of waterfowl in California and Utah, and an epizootic in 1952 killed 4 million to 5 million waterfowl across the western United States. Avian botulism affects the peripheral nerves that control voluntary muscles, resulting in varying degrees of paralysis, including symptoms such as listlessness, sagging head (sometimes called “limberneck”) and drooping wings. Other field signs include paralysis of the inner eyelid, birds propelling themselves across the water using their wings and windrows of carcasses coinciding with receding water levels. While some forms of botulism can affect humans, waterfowl are typically affected by Type C botulism, which has not been found to affect humans. In addition, thorough cooking kills the botulinum toxin in food.
Lead poisoning, which occurs when waterfowl ingest spent lead shot, is a unique disease because it is caused entirely by humans. Ingestion of just a few pellets can cause death, and in some cases, a single pellet may prove lethal. At one time, an estimated 3,000 tons of lead shot were being deposited by hunters in North American wetlands each year, and the number of spent pellets in some wetlands averaged nearly 70,000 per hectare. Within the United States alone, historic annual losses of waterfowl from lead poisoning were estimated at between 1.6 million and 2.4 million birds. Afflicted birds often take several weeks to die and are characterized by an unwillingness to fly, “roof-shaped” wings, severe emaciation, including a condition known as “hatchet breast,” and bright green staining around the vent. While some lead hot spots remain and periodic die-offs still occur, the introduction of nontoxic shot has curtailed lead shot deposition in North American wetlands and has become a viable long-term solution to lead poisoning.
While it is unclear how many North American waterfowl actually succumb to disease each year, it is clear that continued wetlands loss will force larger numbers of waterfowl into a smaller number of suitable areas, increasing their risk for exposure to pathogens and major disease outbreaks. Through habitat conservation programs, Ducks Unlimited is working to minimize waterfowl losses to disease and ensure a healthier future for North American ducks and geese.
Dr. John M. Coluccy is a regional biologist and Nathan Pfost is a conservation intern at DU’s Great Lakes/Atlantic office in Ann Arbor, Michigan.