“When we’re out here doing migratory bird studies, we might see some and then we pick them up as soon as possible. A lot of times, we get radioed from different people like lifeguards and they have us come out and pick them up so that the disease doesn’t spread throughout the rest of the ecosystem.”
In some previous years at Presque Isle, hundreds of birds and untold numbers of fish would die in a summer.
The interns found five dead birds rotting on the beach. They buried the maggots around the bird carcasses because they also could carry the botulism toxin. Other birds might eat them and become infected. They shoveled the bird carcasses into a big black plastic garbage bag, the kind that contractors use when removing asbestos.
“If they’re very fresh — this one obviously is not very fresh, but if we get a fresh one, we actually freeze them and they’re sent off to be tested for botulism. But something like this we’ll just bag up until we can get them incinerated to get rid of all the disease.”
A local funeral home handled the incineration.
The frozen carcasses were shipped to the National Wildlife Health Center in Madison, Wisconsin. There, Grace McLaughlin was among the researchers who began to put the puzzle together.
A couple of invasive species were brought in the ballast water of cargo ships coming from eastern Europe. Zebra mussels and quagga mussels created huge mussel beds on lake bottoms. That began a complicated biological phenomenon. Organic matter, mostly dead algae, settled to the bottom among the mussels and decayed there. That, combined with the mussels’ pseudofeces would lower the oxygen level in the immediate area of the mussels. McLaughlin said Type E botulism spores occur naturally, but they began spreading like crazy in this new anaerobic environment.
“That toxin will accumulate in the organic matter as well as in the water in the immediate vicinity of the mussel beds,” McLaughlin explained.
“As the mussels do their filter feeding, they will accumulate the toxin. However, they are not susceptible to the toxin. When the fish start coming down there and eating the mussels, they become intoxicated, lose their ability to swim properly, and become easy prey for the birds that come in.”
And another invader from Eastern Europe, the round goby, was the primary fish feeding on the mussel beds. Researchers made the connection when they noted botulism poisoning started spreading among birds shortly after round gobies arrived in big numbers.
Later, research out of the University of Wisconsin gathered data from volunteers who walked the beaches in Door County, Wisconsin, Sleeping Bear Dunes National Lakeshore in Michigan and in the Upper Peninsula of Michigan. They found botulism deaths also coincided with warmer waters. So, add climate change as a factor.
Researchers also learned that because the mussels filtered microscopic organisms out of the water, it was clearer. Sunlight could reach deeper in the water for more algal growth which would eventually die. Again, that robbed the bottom of oxygen as it decayed, which meant even more botulism spores.
In our reporting archives we found there were larger bird and fish die-offs due to botulism E in 2006, 2007 and others in 2013 and 2016. Nearly every year there are die-offs, but some years are worse than others.
For example, in 2016, about 600 birds died along the shore of Lake Michigan, washing up at Sleeping Bear Dunes National Lakeshore and then there were more dead birds in the Upper Peninsula of Michigan that year.
The really difficult part is predicting exactly when to expect a particularly bad year. Last year in late October when the temperatures were cooler, about 300 birds died at Sleeping Bear Dunes due to botulism. Other years, very few birds die.
Over the decades, though, the death toll has been significant, with numbers in the tens of thousands.
“While we haven’t had large numbers or large mortalities in the more recent years, there have been some years that we’ve had huge mortalities. And so, in 2006, 2007, these estimates were about 7,000-7,500 birds affected. And in 2006, those were primarily common loons. So, you’re talking about thousands of loons,” said Melotti with the Michigan DNR.
