Botulism Blamed in Bird Die-off on Lake Michigan
Fish, Birds Wash Ashore on Local Beaches
By Paul Gingras

Adie-off of birds killed by botulism has been reported along Lake Michigan in Mackinac and Schoolcraft counties, and researchers are now conducting laboratory tests to analyze the birds. While an accurate count is not available, the number of dead birds is estimated in the thousands, according to the Department of Natural Resources (DNR), which has received many reports of dead fish and birds washed ashore on beaches in the area. The DNR has confirmed type E botulism in common loons, redneck grebes, and several more bird species downstate for the second consecutive year.

An abundance of algae in the lakes has contributed to the growth of botulism bacteria, which is eaten by zebra mussels, quagga mussels, and round gobies, which in turn are eaten by birds. Some of the fish and birds that ingest the bacteria sicken and die.

Dead birds were discovered and reported to the DNR throughout October. The department was still sending birds to a downstate laboratory for testing Thursday, November 1, said Cheryl Ozanich of the DNR field office in Naubinway, adding that a similar die-off occurred between late September and late October last year.

The last die-off of this kind occurred in 1983.

In the wild, type E botulism primarily impacts bird populations. Although it is fatal to many animals, including humans, type E botulism is not considered a serious danger to the public by the DNR.

Human poisonings usually result from eating fish and marine animals that are not thoroughly cooked, or are imperfectly canned or preserved, according to a DNR report. Humans seldom eat waterfowl killed by botulism, and cooking eliminates it, so the DNR does not consider wild birds affected by botulism a significant danger to public health.

The DNR advises against touching dead birds without gloves, Ms. Ozanich said.

Often, bird die-offs occur in association with fish die-offs, because decaying fish are fertile ground for the growth of type E botulism.

Dead fish have also been reported locally, Ms. Ozanich said.

Botulism occurs naturally in soil, both on land and under water. Historically, it affected animals when lake temperatures changed in autumn, sediment rose, and fish picked up the bacteria that causes botulism.

Botulism was noted earlier in the year and appears to be the result of invasive species that browse in underwater soil and pick up the bacteria that causes botulism, said Wildlife biologist Thomas Cooley, who is studying the die-off at a DNR disease lab in the Lower Peninsula.

In lower Michigan, type E botulism has killed birds in Benzie, Leelanau, and Emmet counties. Species affected south of the Mackinac Bridge include horned grebes, red-necked grebes, herring gulls, ring-billed gulls, common loons, white-winged scoters, double crested cormorants, long-tailed ducks, and bald eagles.

Dead piping plovers and caspian terns, species considered threatened by the U.S. Fish and Wildlife Service, were found near Sleeping Bear Dunes National Lakeshore. Owing to local regulations, these birds were sent to a federal testing lab in Wisconsin, rather than to the DNR.

Mr. Cooley reported that several factors appear to have contributed to the reappearance of botulism.

Part of the problem is the abundance of a form of naturally occurring green algae called cladophora, which is common in Lake Michigan and Lake Huron. Cladophora creates conditions that spur the growth of a spore-forming bacteria that causes botulism.

The bacteria, Clostridium botulinum, is consumed by invasive species of mussels, such as zebra and quagga mussels, both of which are having a negative affect on the health of the Great Lakes, according to a report by Tip of the Mitt Watershed Council.

In turn, these mussels are consumed by an invasive species of fish called the round goby.

Mr. Cooley reports that the water birds affected by botulism ate mussels or gobys and became sick from a toxin produced by the bacteria they carried.

Not all birds that ingest the bacteria are killed by it, but many succumb to the toxin it produces, Mr. Cooley reports, adding that he is particularly concerned about eagles, which eat large amounts of fish.

Mr. Cooley said other animals that eat infected fish or birds are unlikely to be affected by botulism. Generally, "you do not hear much about type E in canines," Mr. Cooley said.

Dog owners tend to pull their pets away from fish or bird carcasses before they can ingest enough bacteria to be sickened or killed by botulism, and wild canines such as wolves and coyotes are unlikely to ingest enough infected fish or birds to be hurt, he added.

Mr. Cooley emphasized that type E botulism is primarily considered a concern for fish-eating bird species.

Ms. Ozanich said her office has received numerous phone call from the public regarding dead fish and birds.