A paralyzing disease known as botulism has killed over 100,000 birds in parts of the Great Lakes since 1999. The outbreak is particularly harmful to some species of water birds, silencing the haunting call of many common loons and further threatening the federally endangered piping plover.
Scientific mysteries and partially answered questions surround the botulism outbreaks: How does the toxin spread through the food chain? What causes and sustains outbreaks in the Great Lakes? How can it be controlled or eliminated? The U.S. Geological Survey, in collaboration with the National Park Service, U.S. Fish and Wildlife Service and other partners, and funded through the Great Lakes Restoration Initiative, is studying avian botulism to better understand and help mitigate deadly outbreaks in the Great Lakes.
“Botulism, we believe, is a consequence of Great Lakes ecosystems distressed by invasive species and disturbed delicate food webs,” said Jonathan Sleeman, Director of the USGS National Wildlife Health Center. “We are working to detect botulinum toxin in the environment and determine how the toxin reaches and affects birds.”
What is avian botulism?
Avian botulism is a deadly food poisoning of wildlife, caused by a toxin produced by the naturally occurring soil bacterium, Clostridium botulinum. The toxin likely accumulates in some invertebrate and fish species, which are then eaten by vulnerable water birds.
Two types of botulism are deadly to birds such as waterfowl, shorebirds, and colonial water birds. The majority of avian botulism is caused by Type C toxin, which can occur annually on wetlands, lakes, and ponds, while Type E toxin is limited primarily to the Great Lakes (but also occurs in Europe and other locations outside of the U.S.).
Botulism in humans is usually the result of eating improperly home-canned foods, which contain types A or B toxin. Type E intoxication of humans has been associated with improperly smoked fish. Thorough cooking destroys botulinum toxin that may be present in food.
An extensive problem
Outbreaks of avian botulism Type E have resulted in periodic and often severe die-offs of fish-eating birds in the Great Lakes since at least the 1960s, but have become common since 1999, particularly in Lakes Michigan and Erie.For example, in 2012, over 4,000 botulism-afflicted birds were found dead on Lake Michigan beaches.
On a larger scale, the USGS NWHC in Madison, Wisc., has developed an interactive national map showing the number of bird deaths primarily related to botulism Type C, when each outbreak occurred, and the top species affected, based on 25 years of bird mortality data.
At the base of the food web
Spores of the botulism bacterium are widely distributed throughout the environment, but can become active and produce toxins under suitable environmental conditions, such as warm temperatures coupled with the presence of decomposing plants and invertebrates. In some cases, birds may ingest the toxin by consuming decaying organic matter directly, or by eating live invertebrates whose food was laden with the toxin.
USGS and National Park Service scientists are studying potential connections between toxin production, lake-bottom sediment and water conditions, and the presence of invasive species such as zebra mussels, quagga mussels and round gobies. The mussels create a hard surface on the lake bottom which allows algae to attach in places where it could not previously, and the mussels filter lake water and make it clearer. The clear water allows sunlight to reach further down into the lake and, combined with the increase in phosphorus from mussel excretion, human industry and agriculture along the shoreline, promotes extensive growth of the nuisance alga Cladophora. Later in the summer, the alga dies and decays on the lake bottom, creating a low-oxygen environment favorable to the botulism bacterium.
A paralyzing illness
The botulinum toxin attacks birds’ nervous systems by preventing impulse transmission to muscles. Typical clinical signs of botulism in birds include:
Together, these impairments can lead to death by drowning, respiratory failure, or vulnerability to predators.
The USGS and its partners are studying avian botulism on both microscopic and geographic scales as part of the Great Lakes Restoration Initiative. Information gleaned from this research will help resource managers develop strategies to prevent or reduce the impacts of devastating botulism outbreaks in the Great Lakes.
Under the microscope
USGS researchers and their partners are investigating where and how Clostridium botulinum grows in Lake Michigan to uncover factors that cause botulism in water birds.
“Determining precisely where botulism outbreaks occur will allow us to further determine how birds ingest the toxin,” said USGS microbiologist David Blehert. “To facilitate this research, we are working to improve our capacity to detect the botulinum toxin.”
Laboratory tests following necropsies, or wildlife autopsies, are used to determine whether botulinum toxin was a cause of death in birds, and these analyses are conducted at the USGS NWHC. Work is underway to develop novel biochemical tests to more precisely determine the amounts of botulinum toxin in tissues from birds, fish or invertebrates. Molecular tests are also used to determine the amounts of toxin-producing bacteria in environmental samples, such as sand, mud, or water.
From the sky
The USGS Upper Midwest Environmental Sciences Center (UMESC) in La Crosse, Wisc., is studying the distribution, movement, and feeding patterns of water birds to help determine where and how they come into contact with the botulinum toxin. This information will eventually help identify what drives botulism outbreaks in the Great Lakes for wildlife management purposes.
“Our research can help managers effectively focus their conservation efforts,” said USGS scientist Kevin Kenow. “If we know where loons and other waterbirds obtain contaminated food, management tactics can be targeted to those areas.”
Kenow and his colleagues use aerial surveys and tracking technology to determine migration and feeding patterns of the iconic common loon. Satellite
tracking devices implanted in loons from Minnesota, Wisconsin, and the Michigan Upper Peninsula help scientists determine where the birds are spending time on the Great Lakes during their seasonal migrations, and where additional research could focus to provide insight on routes of exposure to the botulinum toxin.
Other loons are tagged with electronic geolocators, which record daily information about the birds’ specific feeding behavior. Geolocator data, such as location, temperature, light levels, and pressure, tell how far down in the water loons dive for fish: Close to 150-foot dives have been recorded, suggesting that loons may be exposed to the toxin in deep offshore waters.
The public can track loon migratory movements from current and previous aerial surveys on the USGS common loon migration page.
On the ground
A beach strewn with lifeless birds is a disheartening sight. However, some citizens have been channeling their concern into action through the Avian Monitoring for Botulism Lakeshore Events (AMBLE) citizen science program. Established by the USGS in 2011, AMBLE trained volunteers to monitor, count, and collect data on bird carcasses found along the shores of northern Lake Michigan. The 2011 AMBLE focus area was Door County, Wisc., and was expanded to include some of the Green Bay shoreline in 2012.
Data collected are entered into an online portal maintained by the USGS NWHC, and especially when combined with data collected by NPS volunteers and biologists around northern Lake Michigan, provide valuable information about the timing, severity, and bird species affected by botulism.
“We are using data collected by beach monitors to create a statistical model, or representation, of the pulses of reported mortality in space and time,” said USGS scientist Jenny Chipault. “Repeat data from 2013 will validate and strengthen the model and ultimately help define Lake Michigan bird mortality trends.”
Data on bird mortality are also being used to help determine the locations of intoxication based on the ecological characteristics of the species involved.
AMBLE volunteers are specifically trained in safe handling and disposal of wildlife carcasses they may find.
“In general, untrained people should not pick up or touch sick or dead wildlife,” said Stephen Riley, USGS scientist and lead of the Great Lakes botulism study “Instead, they should alert their state wildlife officials about the location, and those officials will properly dispose of the carcasses.”
For more information on USGS avian botulism and wildlife disease research, please visit the following websites:
USGS National Wildlife Health Center: http://www.nwhc.usgs.gov/disease_information/avian_botulism/index.jsp
USGS Upper Midwest Environmental Sciences Center: http://www.umesc.usgs.gov/umesc_home.html
Great Lakes Restoration Initiative: http://cida.usgs.gov/glri/projects/habitat_and_wildlife/avian_botulism.html
USGS Michigan Water Science Center: http://mi.water.usgs.gov/
USGS Great Lakes Science Center:http://www.glsc.usgs.gov/
Restoring the Great Lakes, DOI publication on the Great Lakes Restoration Initiative (PDF file): http://greatlakesrestoration.us/pdfs/doi-glri-report-20131028.pdf
USGS Common Loon Migration Page: http://www.umesc.usgs.gov/terrestrial/migratory_birds/loons/migrations.html
USGS AMBLE citizen science program: http://www.nwhc.usgs.gov/amble/
USGS National Atlas Avian Botulism Wildlife Mortality Information: http://www.nationalatlas.gov/mld/wlbotut.html
Wildlife Health Event Reporter: http://www.whmn.org/wher/