(Image: Laysan duck with four ducklings. USFWS photo.)
The cause of the fatalities is still not known, and duck carcasses are being flown to the Mainland for testing.
But the best guess right now is that the birds are getting something fatal from their water, and that it might be avian botulism.
In humans, botulism generally comes from eating improperly home-canned foods. The bacteria can grow outdoors in warm, stagnant waters, where they feed on rotting vegetation and bugs. Birds can get the disease directly from the water or from eating affected bugs.
The toxin produced by the botulism bacterium causes paralysis and ultimately death.
“Birds are unable to use their wings and legs normally or control the third eyelid, neck muscles, and other muscles. Birds with paralyzed neck muscles cannot hold their heads up and often drown. Death can also result from water deprivation, electrolyte imbalance, respiratory failure, or predation,” says the U.S. Geological Survey National Wildlife Health Center website, http://www.nwhc.usgs.gov/disease_information/avian_botulism/index.jsp.
Wildlife noticed birds dying at Midway Aug. 10, and since they suspected avian botulism in stagnant water, they began flushing the freshwater seeps where the birds gather. The daily death count has begun dropping, perhaps as a result of those measures, according to the U.S. Fish and Wildlife Service.
Midway Atoll is the second-westernmost island in the Hawaiian archipelago, and lies more than 1,000 miles to the northwest of Honolulu. It is a national wildlife refuge and lies within the Papahānaumokuākea Marine National Monument.
Laysan ducks were once found throughout the archipelago, but by the mid-1800s, they were only surviving in the wild at Laysan Island, a low, sandy island with a large saltwater lake. Laysan lies several hundred miles west of Kaua'i.
They are the rarest waterbird in the United States.
Four years ago, to provide a safety net in case of natural disaster at Laysan, 42 ducks were taken to Midway, where they quickly began reproducing. By this year, the count had gone up nearly 10 times. Before this week's disease outbreak, there were about 400 ducks on the atoll, meaning a quarter of the population has died in a week.
At Laysan itself, the population rises and falls, but it was most recently estimated at 600 birds. The disease outbreak has not been reported from Laysan, where a small crew of wildlife experts keeps watch.
At Midway, as of August 15, 106 birds were dead. A U.S. Fish and Wildlife Service official said 69 percent of the dead birds were youngsters from this year's hatchings.
Most of the dead birds have been burned to control the disease. A sampling has been preserved and was flown to Honolulu yesterday, for further shipment to the National Wildlife Health Center in Madison, Wisconsin.
“Although we suspect avian botulism, we will not have a confirmed diagnosis until next week,” said Matt Brown, Midway 's acting refuge manager.
“As recommended in these cases, we have added large amounts of fresh water to many of the wetland seeps where dead birds have been found in order to reduce stagnation.”
The Laysan duck deaths represent the loss of 10 percent of the wild population of Laysan ducks in less than a week. Brown said the situation “underscores the need to have Laysan ducks at more than one location in the Hawaiian Islands.
© 2008 Jan TenBruggencate