Lake invaders may be killing birds

Scientists suggest invasive mussels in the Great Lakes may be responsible for the deaths of thousands of migratory birds.

The hunt is on in the upper reaches of Lake Michigan to count what's believed to be thousands of bird carcasses that have washed ashore this fall — a staggering toll blamed on the disruptive powers of invasive species that have taken root in the Great Lakes.


The great debate in the Asian carp crisis, still playing out in federal court and the halls of Congress, is whether the feared fish has the capability of establishing a thriving population in the Great Lakes. If so, bighead and silver carp will almost certainly, and dramatically, alter commercial and recreational fishing in the nation's largest freshwater body.

But what if, as some scientists suggest, the Great Lakes' natural defenses — plankton shortages, lower water temperatures, greater water depth and swift-moving currents — keep Asian carp from sustaining themselves in large numbers? Will the threat have been avoided?

The answer is that all invasive species bring consequences that few can predict, leading scientists to ponder the thousands of gulls, loons, mergansers and other migratory birds whose remains wash ashore along the white-sand beaches in northern Wisconsin and Michigan's upper peninsula each fall.

There is a somewhat controversial theory for this annual die-off, which by some estimates has claimed more than 100,000 birds in the last 15 years, and it involves a type of naturally occurring but deadly botulism linked to the spread of invasive zebra and quagga mussels, which entered the Great Lakes decades ago aboard ocean vessels.

"There's still a lot about this we don't know," said Joe Kaplan, of the Michigan-based nonprofit Common Coast Research & Conservation. "The one thing we do know is that it's killing a lot of birds that are important to us.


"This is a very serious problem that deserves more attention."

Like Asian carp, zebra and quagga mussels reproduce rapidly and overwhelm their environment. Scientists feared densely packed clusters of mussels would take a toll on industry, colonizing in water pipes, intake valves, and air conditioning and cooling systems. And they have.

The U.S. Geological Survey, which has studied zebra and quagga mussels for more than 20 years, rank them among the most destructive "biological invasions into North America." But few could foresee the carnage that has followed.

Zebra mussels and quagga mussels filter naturally occurring botulism and other toxins from the water. Round gobies, another problematic invasive species, eat the mussels, and birds, in turn, eat the gobies.

"The evidence is there to suggest this is happening, but it's circumstantial evidence because we haven't found any proof of it," said Tom Cooley, a biologist at the Michigan Department of Natural Resources. "All we can really do at this point is to continue to monitor what's happening and maybe something in the lakes will turn around."

Michigan's DNR and the Common Coast Research & Conservation are among the organizations, including the USGS and the National Wildlife Health Center, studying the deadly phenomena that this year is expected to kill as many or more birds than died in the oil spill in the Gulf of Mexico last summer.

Scientists don't know how long botulism or similar toxins have been killing birds in the Great Lakes, but the first sizable counting came in 1999, when researchers recorded 311 birds off the shores of Lake Erie. The following year, they found 8,000 around the Great Lakes and the death counts have remained in the thousands every year since.

For now, the deaths appear limited to the northern Great Lakes region, where the concentrations of mussels and birds are higher. But so little is known about the environmental factors that contribute to these deaths that scientists can't rule out large numbers of dead birds washing up along the shore closer to Chicago and western Michigan.

After two "low years" the death toll seems to have risen again this fall, Kaplan said, with perhaps as many as 50 dead birds recovered for every mile of beach. That may be because the unusually hot summer around the Great Lakes produced more algae, which feeds the mussels' population explosions. Or it may be attributed to other factors scientists haven't yet explored.

"We're still learning," Cooley said.

The die-off has devastated the populations of a number of important and protected bird species, but the discovery of many hundreds of common loons, a threatened species in Michigan, has given researchers a rallying point to draw attention and hopefully more funding to this issue, Kaplan said.

But with so much money already being spent to minimize the spread of invasive species within the Great Lakes, and recently to stop another from entering, Kaplan said he realizes this fight may be unwinnable.

"Unfortunately, we don't begin to really study an issue until we see entire systems collapse or get out of control," Kaplan said. "But that comes at a high cost."

By Joel Hood, TRIBUNE REPORTER

http://www.chicagotribune.com/news/local/ct-met-lake-michigan-bird-deaths-20101127,0,918715.story