Waterfowl Botulism in Michigan: The what and why of the bird die-off of fall 2012
Hundreds of waterfowl were found dead along the northern Lake Michigan shoreline last fall as the result of Type E botulism. Scientists now suspect invasive species in Lake Michigan’s food web as culprit to die-off.
A significant waterfowl botulism kill was experienced along the northern Lake Michigan lakeshore during the fall of 2012. A variety of waterfowl species, the largest number being common loons (Gavia immer), were impacted by Type E botulism and found, geographically, in a general area from Manistique, Michigan down to about Frankfort, Michigan (Schoolcraft , Mackinac, Emmet, Charlevoix, Antrim, Leelanau and Benzie Counties). Perhaps you read of the banded loon, nicknamed The Patriarch, found dead along the shore near Northport, Michigan in late September, 2012. This bird was confirmed positive for Type E botulism. The Patriarch, born in 1991, lived the majority of his life near the Intermediate River in Lake Bellaire and was the oldest banded loon in northern Michigan reaching age 21. The Patriarch certainly had a productive life (and may now have 16 living offspring), but for loon researchers and interested citizens, his demise from botulism was quite discouraging.
The bacterium Clostridium botulinum, which produces the botulinum toxicant under certain circumstances, is native to the Great Lakes. There are documented years in the 1960s, 1970s and early 1980s (pre-zebra/quagga mussel, pre-round goby fish) where there were notable botulism impacts to loons and other species. Today, the weight of evidence points to increased frequency of avian botulism in the post-invasives food web now existing in Lake Michigan. This article will describe some details from the recent impacts in 2012, the Lake Michigan food web, as well as some of the understanding related to the mechanisms, which enable the botulism toxicant to be available in the food supply of these waterfowl.
Species and numbers of waterfowl killed during fall 2012
As mentioned earlier, the waterfowl species most impacted in terms of carcasses found was the common loon. The other most common species killed were also fish-eating ducks including red-necked grebes, horned grebes, long-tailed ducks, white-winged scoters, double-crested cormorants, herring and ring-billed gulls and smaller numbers of merganser species. The majority of the loons and other waterfowl impacted are typically Canadian birds, which are on their annual migration cycle and stop over on the Lake Michigan shore for feeding before continuing on to the Chesapeake Bay area or Gulf of Mexico.
Actual kill numbers are only best estimates, but dedicated volunteers—beach rangers—have been very helpful making these estimates in many areas including in Antrim and Charlevoix Counties. The Sleeping Bear Dunes National Lakeshore had 19 volunteers donate 930 hours monitoring and walking beach segments over the summer and fall. In the Sleeping Bear Dunes along a two-county shoreline (Benzie & Leelanau counties), 580 common loon kills were documented in fall 2012, the largest number of loons since annual counts began in 2006 within the Lakeshore. I can verify from reports and personal observations of at least 100 other loons in other parts of Leelanau County, mostly near Leland. Loon researchers from Commoncoast.org reported 247 loons east of Manistique, Michigan, and volunteer reports were submitted of up to 20 loons in Antrim and Charlevoix Counties. The Emmet County shoreline also had high numbers of loon losses (no good count estimate available yet). This would put a conservative total estimate to be at least 1000 loons lost this fall, including both juvenile and adult birds. Mid-October to mid-November was the highest die-off period, likely corresponding to bird migration cycles. For other species, a conservative kill estimate might be around 500 for grebes, 500 for long-tailed ducks, 500 for double-crested cormorants, and perhaps 250 for white-winged scoters and 250 for gull species.
The Lake Michigan Food Web
While the food web of Lake Michigan has undergone many changes in the 1900s (i.e. sea lamprey, alewife, introduction of pacific salmon), it is unquestionable that the food web has changed radically since the late 1980s and early 1990s when the invasive zebra and quagga mussel, and the round-goby fish, took hold. Water clarity in Lake Michigan has at least doubled since then, due to the massive filtering of the quagga mussels, whose numbers are now estimated in the 950 trillion range in Lake Michigan. With this filtration, light penetrates deeply into the water allowing native algaes to thrive and grow at deeper depths than ever before. The post-invasive food web is thought to account for the increased frequency of avian botulism in the past ten years.
In the Great Lakes, botulism spores (the resting stage of the bacteria) are naturally abundant in various habitats, such as soils and aquatic sediments, and persist over many years in this inert spore stage. The problem begins when the correct environmental factors are present for the spores to germinate and begin toxin production. When algae, such as Cladophora, wash ashore and decompose, there can be a loss of oxygen in the substrate area and the Closteridium botulinum spores can germinate, allowing one of nature’s most potent toxins to become bio-available in the environment. The toxin causes a neuromuscular paralysis in fish, birds and mammals, but does not impact invertebrates and quagga mussels. Fish, like the abundant and invasive round goby, eat the mussels and invertebrates and can become paralyzed, losing equilibrium in the water. The loons and other waterfowl consume these easy-to-catch toxin-rich fish and experience paralysis. The botulism disease in waterfowl is often called limberneck, because the birds often lose the ability to hold their neck upright and may actually drown. Carcasses tend to wash ashore during—and are most abundant—after storm events pass through.
In Northern Lake Michigan, there was a vastly significant waterfowl kill due to botulism in the fall of 2012. However, there was almost a non-existent botulism kill in the fall of both 2011 and 2010, with very small numbers in 2009 and 2008, after significant kills in 2006 and 2007. There are many factors yet to be fully understood, but the recent cycle is undoubtedly related to the post-invasive food web that has taken hold of the Great Lakes. Avian botulism kills do not occur along inland-lakes, and humans cannot get botulism from swimming in the Great Lakes, but efforts to keep additional invasives out of the Great Lakes and inland lakes are important.