Botulism Kills Laysan Ducks on Midway
Hawaiian Atoll Staff Works to Reduce Losses of Rare Bird Species
Aug 27, 2008
Laysan ducks (Anas laysanensis) were translocated to the refuge in 2004 in an effort to prevent extinction of this species. The main population of what is considered the rarest native waterfowl in the United States, which is on Laysan Island, is not expected to be affected by the botulism outbreak
The Laysan Duck
Laysan ducks are found only on Laysan Island, which is part of the Hawaiian Islands National Wildlife Refuge, and now on Midway Atoll National Wildlife Refuge. Birds on Laysan Island were heavily exploited when explorers came to mine guano in the late 1800s. In addition to the mining operations, hunting for food and sport took a toll on the Laysan duck. In 1911, only 11 of these rare birds were found on Laysan.
By 1987 the population had reached approximately 500 animals. But climate fluctuations, such as El Nino events, cause Laysan duck population fluctuations as well. During a 1993 drought it is believed that their numbers dropped to less than 200.
In 2004, in an effort to ensure that a catastrophic event on Laysan Island did not result in extinction for these birds, 42 wild Laysan ducks were introduced to Midway Atoll. Captive breeding populations around the world also contribute to the effort to prevent extinction for the species.
The Botulism Outbreak on Midway Atoll
The first case of avian botulism in the Midway Atoll Laysan ducks was found on August 10, 2008 but it took several weeks to determine the cause of death. In the interim more than 120 ducks have died.
Initially there were concerns that the birds might be suffering from avian influenza, which can be transmitted to humans. This meant that strict precautions had to be taken when collecting carcasses to prevent infecting workers in the area.
Now increased effort can be put into collecting carcasses and, more importantly, to preventing the spread of the disease. Because avian botulism is spread in stagnant waters during warm weather, the first step taken was to drain the catchment basin near where the ducks nest. Then fresh water was introduced into wetlands on the island to help ensure that no further outbreaks occur.
The Outlook for the Species
Before this botulism outbreak the Laysan duck population on Midway Atoll was approximately 400 birds. Of those 400, nearly 200 fledged this year. If next year’s breeding season is as successful, the population on Midway Atoll should come close to recovery in a year or two.
The main population of approximately 600 ducks, on Laysan Island, is over 100 nautical miles away, so this outbreak will not be a problem for them. But this situation has meant that the US Fish and Wildlife Service, which is charged with protecting the Laysan duck, is taking a hard look at ways to prevent another outbreak on either island.
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