2 weeks Ago By [email protected] (Robert (Bob) Bowles)
Every year in late summer and early fall, dead bodies of water birds are found along the shores of the Great Lakes and, to a lesser extent, on inland lakes. Common loons, ducks, geese and sometimes gulls are affected. Some years are worse than others and during the summer of 2002, a record high of 14,000 birds washed to the shore of Lake Erie and, before that, more than 10,000 dead loons on the Great Lakes in one year.
These deaths are attributed to avian botulism, also called western duck sickness, which acts like food poisoning and can reoccur. The bird ingests a toxin produced by the bacteria Clostridium botulinum and become paralyzed and unable to hold their heads up (called limpneck). Their heads fall into the water and the bird drowns.
Birds that are able to struggle ashore are unable to move and die from the cold, respiratory failure, or a predator. Birds can recover if kept warm and safe in a sheltered location. This bacterium is widespread in soil, living for a long time and requires warm temperatures, a protein source, and an anaerobic (no oxygen) environment in order to become active and produce the toxin.
These conditions are more prevalent in our lakes now with warmer temperatures and higher nutrient loading causing more plant growth resulting in more decomposing vegetation which causes lower oxygen levels. A wide variety of birds and some mammal species are susceptible to the disease and databases have been compiled in recent years to monitor these deaths and those from lead poisoning. Clostridium botulinum is a common soil bacterium in local aquatic lake sediment ecosystems which produces toxins labelled from type A to G.
Types C and E are known to cause neuroparalytic illness (botulism) in fish and birds. Type C botulism toxin affects ducks and shorebirds, and type E affects gulls and loons. Avian botulism is one of the most significant diseases of migratory birds; estimates suggest 10,000-50,000 birds are lost in most years.
The disease is spread to other birds by maggots and other invertebrates that feed on the decaying carcasses. The toxin builds up in these invertebrates but does not harm them. However, there is enough toxin in one maggot to kill the bird that eats it.
The bacteria botulism spores can survive in wetland soils for years and are ingested by birds while feeding on vegetation. These spores grow the bacteria that produces the toxin since conditions are ideal with protein rich material, absence of oxygen, and high temperatures. The maggots on the dead carcasses spread the disease, completing the cycle and involving more and more birds.
Research to date has concluded that carcass cleanup does not reduce bird mortality. Avian botulism cannot be prevented but research efforts are to minimize or reduce bird deaths and reduce the exposure to humans and other mammals. Cattle sometimes ingest toxic maggots floating on the water.
Zebra mussel beds filter lake sediment concentrating the bacteria and the introduced round gobies feed on the mussels again increasing the concentration. Larger fish and birds feed on the gobies, again increasing concentration. Bottom feeding fish and birds like lake sturgeon, diving ducks (surf scoters, long-tailed ducks, mergansers) and gulls are more susceptible.
Waterfowl and shorebirds are most susceptible with filter feeders and dabblers like mallards, teals and shovelers at risk due to feeding habits. Fish eating loons and gulls are at high risk, swans, mergansers and grebes at lower risk. Botulism can occur in all birds and mammals that eat the dead fish or birds.
There have been large botulism kills of birds in Lake Huron and Lake Erie since 1998 and it has killed many birds in Georgian Bay in October 2007, 2011, 2012, 2021 and now in late October 2024, dead birds are again beginning to appear washed up on the beaches of Wasaga and Tiny beaches. If birds are rescued before drowning, they can be saved by bird rehabilitators like Shades Of Hope in Pefferlaw. Dead fish and birds on beaches will continue into November until the weather turns colder, or most birds have moved south on their migration.
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