2017-11-16 / Outdoors

Disease takes toll on bird species

By Patti Brandt Burgess
Of The Enterprise staff


THIS DEAD common loon, which likely succumbed to the botulism toxin, was found Friday on a beach north of the National Lakeshore by loon researcher Damon McCormick, who is with Common Coast Research & Conservation. Pyramid Point is visible in the background. 
Photo credit:Damon McCormick THIS DEAD common loon, which likely succumbed to the botulism toxin, was found Friday on a beach north of the National Lakeshore by loon researcher Damon McCormick, who is with Common Coast Research & Conservation. Pyramid Point is visible in the background. Photo credit:Damon McCormick There is no end in sight for bird dieoffs from avian botulism, the paralytic and usually fatal disease that has affected local and migrating bird populations across Lake Michigan since about 2006.

And the common loon is the bird most susceptible to the die-off, according to Damon McCormick, a wildlife biologist with the non-profit Common Coast Research & Conservation.

While the number of birds that have succumbed to the disease along the Lake Michigan shoreline this year is down — about 600 so far — the percentage of deaths that is loons — 60 to 70 percent — is higher than in past years, McCormick said.

“There is no end in sight,” McCormick said, as the botulism toxin is driven by invasive species. “The Lake Michigan food bed is impacted by invasive species so that it’s difficult to predict what’s going to happen going forward.”

The Sleeping Bear Dunes National Lakeshore is the most heavily impacted area, though dead birds are being tracked annually along a 138-mile stretch of Lake Michigan shoreline in the northern lower peninsula and the upper peninsula.

Counts are done by Common Coast, by the Tip of the Mitt Watershed Council and by volunteers in the Lakeshore known as the Bot Squad.

And while it’s unclear whether avian botulism can be called an epidemic across all bird populations, it is an epidemic for loons and can severely impact the loon population in Michigan, McCormick said.

It already has, in fact.

In 2012, which had a March warmup that hit 80 degrees, 1,446 dead birds were found on beaches within the National Lakeshore, according to Bot Squad counts.

That year was also the largest die-off of loons, with 580 loon deaths recorded.

The following spring a 23 percent drop in the loon population was seen — an unprecedented one-year decline, McCormick said.

“When we see that a quarter of the loon population can be lost to botulism ...” McCormick said. “If that happens on a regular basis the Michigan loons are in really bad shape.”

Last year a total of 805 dead waterbirds were counted in the Lakeshore, with 46 of them loons. But across the Lake Michigan region a total of 3,505 dead birds were counted, with 522 of them loons.

Erica Plesha, avian botulism crew lead for the National Lakeshore, said the bird die-off historically peaks in October. In the Lakeshore this year 67 dead birds were found from Oct. 22 to 27. Of those, 45 were loons, Plesha said.

“It’s a little bit later this year than last year, but we had that warm spurt,” Plesha said.

Last October 200 dead birds washed up in Good Harbor Bay, she said.

But what’s been documented reflects a very small part of the total, McCormick said, as loons that die on Beaver and Gull islands, the Manitous and the Foxes are not monitored.

“That’s one of the great unknowns because nobody is out there,” he said. “What’s been documented reflects a very small part of the shoreline.”

The loon is an iconic species that is a barometer for assessing what is happening here to all birds, McCormick said.

The loon was found all across Michigan in the 1800s and early 1900s, but has retreated north following the development of the state’s many lakes.

The first survey of loon numbers was done in 1980 and estimated there were just 800 nesting pairs left in the state, prompting the state legislature to place the bird on the threatened species list, where it still remains.

The Lake Michigan shoreline seems to be ground zero for avian botulism, as migrating birds stop there to eat after their long flight across the lake from points north.

Prevailing westerly winds play a large role, as the birds die on the lake and are pushed to the eastern and southern Lake Michigan shoreline. Researchers also know that warmer water temperatures are a trigger for the toxin, while high water levels seem to keep it more at bay.

Thousands of loons have been banded at Seney National Wildlife Refuge in the Upper Peninsula, McCormick said. Many of them have been found dead on the Lake Michigan shoreline, he said.

The loon, which has been documented as living up to 40 years, has only one or two chicks per year and is sensitive when it comes to nesting.

The bird likes to nest in areas buffered from the mainland such as wetlands, protected areas and islands — including those in northern Lake Michigan, McCormick said.

Avian botulism became more widespread in the Great Lakes with the introduction of the invasive zebra and quagga mussels in 1988 and 1989 respectively. Both quickly colonized and are now found in all five Great Lakes.

The mussels begin the process that ends in production of the botulism toxin by eating microscopic zooplankton, which makes the water clear. The clear water allows the sun to penetrate to a greater depth, signaling the proliferation of native cladophora algae.

When the algae decomposes it consumes oxygen in the water and the deoxygenated water, along with phosphorus and nitrogen waste produced by the mussels, prompts the botulism bacteria to create the deadly botulism toxin.

Loons and other birds that feed on fish and mussels are particularly susceptible to the botulism toxin. Loons can dive up to 150 feet to get a meal and they and other migrating birds pick up the toxin by eating mussels off the lake floor.

Round gobies, an invasive fish species, also play a role by eating the algae. The toxin moves up the food chain when water birds eat the gobies.

Return to top