Montana Fish Wildlife & Parks biologists have completed an investigation into a waterfowl die-off at Lake Frances experienced near the town of Valier in north central Montana.

The die-off was the result of avian cholera and happened in early April. FWP game wardens collected approximately 200 carcasses along the shoreline of the lake after members of the public began reporting the dead waterfowl. Two samples were sent to the National Wildlife Health Center in Madison, WI, which confirmed the cause of mortality to be avian cholera.

Species affected were mainly snow geese, but smaller numbers of northern pintail and northern shoveler ducks were also found along with Canada geese, wigeon and swans. Total mortality for the outbreak is estimated to be around 500 birds.

Avian cholera is a highly contagious disease among waterfowl that become congregated during migration and has been reported in Montana in the past. Mortality events and numbers can sometimes be large. Epidemics of avian cholera occur almost annually in wild waterfowl in parts of North America and is one of the most significant diseases affecting wild waterfowl on the continent.

The bacteria that causes avian cholera does not typically cause infections in mammals and is considered a low risk to humans. But as a precaution, the public should not handle dead waterfowl, and dog owners should prevent contact between their pets and carcasses.

FWP staff have removed as many bird carcasses from the water as possible, but some birds in willow patches were unable to be reached. Waterfowl have continued their northward migration and the large congregations of birds have largely dispersed. The current mortality event has largely ended, but the public may continue to see birds die in small numbers.

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