Avian botulism in Hawai‘i wetlands monitored

HONOLULU — Hundreds of birds in Hanalei’s wetlands succumbed to a botulism outbreak earlier this year. Now the toxin has been detected on Maui, where dozens of Hawaiian birds have been found dead recently, according to officials from the state Department of Land and Natural Resources.

Wetland biologists and others involved in managing lands with associated wetlands have been notified by DLNR Division of Forestry and Wildlife of a recent avian botulism outbreak affecting waterbirds on Maui, states a DLNR press release Friday.

In just over a week, 67 birds have been found dead at Kanaha Pond Wildlife Sanctuary in Kahului including Hawaiian Stilt, Hawaiian Coot, and Hawaiian Ducks of adult and juvenile stages. The paralytic disease has killed adult birds on their nests, also causing the eggs to be lost.

Earlier this year a botulism outbreak in Hanalei, Kaua‘i resulted in more than 300 sick and dead birds being collected by U.S. Fish and Wildlife Services refuge staff.

Additionally, numerous other botulism fatalities have also been reported at wetlands throughout the state.  

Because botulinum toxin can be produced in most wetlands and transported to new wetlands by dead or dying waterfowl, landowners and managers, public and private, are being asked to frequently survey their wetlands for sick and/or dead birds, remove any dead or dying birds from the wetland, and contact local DOFAW biologists for guidance.

Botulism is a paralytic condition brought on by the consumption of a naturally occurring toxin produced by the bacterium Clostridium botulinum. It is an intoxication rather than an infectious disease.

Botulism, type C is commonly found in Hawaiian soils and is not dangerous to humans.

Particular environmental conditions in wetlands will sometimes allow this bacterium to produce botulinum toxin; the toxin is then accumulated in aquatic invertebrates. It is consumption of these toxic invertebrates by waterfowl that leads to mortality.

Typical clinical signs in birds with botulism include weakness, lethargy, and inability to hold up the head or to fly. For waterfowl, this can be catastrophic because inability to hold up the head leads to drowning.

In Hawai‘i, birds commonly affected include waterfowl frequenting wetlands such as our endangered Hawaiian coots, Hawaiian ducks, Laysan ducks, Hawaiian moorhen, Hawaiian stilts, Black-crowned night-herons, and various migratory waterfowl and shorebirds.

Northern Shovelers — a common migratory duck in Hawai‘i — are particularly sensitive indicators of botulism because they are efficient filter feeders and thus are most likely to accumulate sufficient toxin to kill. Avian botulism does not affect humans.

The U.S. Geological Survey National Wildlife Health Center Honolulu Field Station has been working closely with the USFWS and DLNR to investigate and confirm botulism as a cause of waterfowl mortality in Hanalei and Kahului.

The NWHC- HFS provides technical assistance to federal, state, municipal, and non-governmental organizations on wildlife health related matters in Hawai‘i and the Pacific.

“Part of our role is to determine the cause of death during unusual wildlife mortality events involving native and endangered species and provide management recommendations to address and mitigate such mortalities” said Dr. Thierry Work, Wildlife Disease Specialist for USGS NWHC-HFS. “For this particular event, our team first conducts necropsies of freshly dead birds here in Honolulu and then sends samples to the National Wildlife Health Center in Madison Wisconsin for confirmation of botulism.”

There are several types of botulism toxin, some of which can affect humans who eat improperly canned foods.

Although avian botulism Type C does not pose a risk to humans, carcass removal should involve standard hygienic practices including gloves, boots and coveralls.

Officials are asking the public to report waterbird deaths at their local DOFAW office. The DOFAW Kaua‘i branch is at 3060 ‘Eiwa St., room 306, Lihu‘e. The office can also be reached at 274-3433.

Visit www.nwhc.usgs.gov/hfs/Botulism.jsp for more information.

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