Dead Ducks On Local Beaches Succumbed To Avian Botulism, Says National Lakeshore Biologist

Reports of dead or sick ducks on the Lake Michigan shoreline have been circulating among Leelanau locals — from Esch Road beach within the Sleeping Bear Dunes National Lakeshore to Leland’s public beaches. “Unfortunately, they are a common victim in the type-E avian botulism outbreaks that occur in our area this time of year,” shares Vince Cavalieri, wildlife biologist with the National Lakeshore.

Periodic outbreaks of type-E avian botulism have occurred in the Great Lakes since the 1960’s but have become more common and widespread in recent years. The toxin production occurs only when suitable environmental conditions allow spore germination and cell growth. The resulting neurotoxin causes paralysis and is usually fatal. 

Most of the dead birds found in recent days are long-tailed ducks, which Cavalieri says are migrating through coastal Northern Michigan right now, with some staying through the deep winter if Lake Michigan doesn’t freeze.

Some of these migratory sea ducks found on the beach are missing their heads — certainly a macabre sight, but one Cavalieri says is common. Birds that die of botulism are often scavenged. “The usual suspect scavengers —crows, gulls, eagles, coyotes, and raccoons — would do it,” says Cavalieri. In addition, he notes, “owls do commonly eat just the head and neck of their prey as ‘optimal foraging.’ That is the most nutritious part for them to eat and they are relatively well fed so they just eat that part.”

Any wildlife scavengers who happen upon birds infected with type-E avian botulism are likely to get sick, too. “Because of this, it’s also a good reason to keep dogs on a leash to make sure they don’t get into anything bad,” notes Cavalieri. To prevent further spread of disease “on beaches within the park, the avian botulism monitoring crew made up park staff and volunteers will bury the carcasses,” says Cavalieri.

In addition, according to the Lakeshore, “Some bird carcasses are sent to a lab for testing; all birds are documented as part of an on-going avian botulism research project, where  the National Park Service and research partners are analyzing data collected on beaches and at several sites located within Lake Michigan.” This research effort is ongoing and is “being used to improve understanding of toxin transmission through the food web to birds, to develop predictive models of future outbreaks, and to identify management actions that could reduce future avian mortality events.”

The public’s reports of dead birds include beaches both within and close to the National Lakeshore, but Cavalieri says numbers in the park itsef are down overall: “At the park this [past] week we are seeing a bit of a die-off — with about 20 birds found so far. But there have not been a lot of carcasses this year compared to many recent years.”

Cavalieri explains that while the botulinum bacteria are naturally occurring in Lake Michigan’s cladophora algae mats and “probably have always posed some threat,” it is believed that invasive zebra and quagga mussels (that were transported to the Great Lakes region through ballast water discharge from ocean-going ships) have changed the lakes to a degree that makes type-E botulism more likely to occur.

“Basically, zebra and quagga mussels filter the lake of particulates which allow sunlight to penetrate deeper into the water column where the cladophora algae grows,” he says. When the algae dies, it forms mats that have the perfect anaerobic conditions in which the botulinum bacteria thrives. “That bacteria produces a toxin that is taken up by small invertebrates and eventually into fish and birds that eat them.”

The biologist stresses that it is illegal for park visitors to handle or remove sick birds from the shoreline. “You can contact the park to report them,” says Cavalieri, adding, “Even [those discovered] outside the park but nearby are of interest.” A complete list of who to contact for safe and legal handling and disposal of birds can be found here. 

Pictured: National Park Service photo of a deceased long-tailed duck found on the Lake Michigan coastline.