Laysan ducks, one of the world's most endangered waterfowl, are native to only the Hawaiian archipelago. For 150 years, Laysan ducks were restricted to an estimated 4 square kilometers of land on Laysan Island in the northwestern Hawaiian Islands. In 2004 and 2005, in an effort to rebuild the population, biologists released 42 Laysan ducks on Midway Atoll, located one day's boat ride from Laysan.
By 2007, a breeding population was well established on Midway, reaching 200 ducks. However, in August 2008, more than half of the Midway duck population (181 ducks) was lost to a disease epidemic lasting 30 days. Necropsies (the animal equivalent of autopsies) on dead birds revealed botulism type C as a cause of the die-off.
Disturbingly, said Work, 3 ducks were also infected with a worm suspected to be Echinuria uncinata; this worm has been responsible for mass die-offs of Laysan ducks on Laysan Island. Work notes that this worm was either moved to Midway during translocations of ducks from Laysan, despite preventive treatment of all founding birds, or it arrived with migratory waterfowl.
Either way, says Work, this epizootic highlights the disease risk to birds restricted to small island populations and the challenges associated with managing newly translocated endangered species. Frequent population monitoring for early disease detection and comprehensive wetland monitoring and management will be needed to offset the potential effects of avian botulism and parasitism on endangered Laysan ducks, Work said.
The bigger picture, though, is that disease risks need to be closely examined for translocations of all kinds, especially in light of translocations being proposed for dealing with habitat range changes that affect endangered species due to climate change.
This research was presented by the USGS at the Wildlife Disease Association Conference in the first week of August, 2009.
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