Newcastle disease, which has hit hard in past summers, is suspected of killing cormorants and other birds on two lakes. still, other years' outbreaks have been worse.
Hundreds of cormorants, pelicans, gulls, herons and egrets are dead on two lakes in west-central and southern Minnesota, most likely the result of a virus that strikes wild birds every other summer.
Following a tip from Ontario, Department of Natural Resources officials began investigating Minnesota lakes; they discovered carcasses and obviously ill birds at Pigeon Lake, near Litchfield, and Minnesota Lake, southeast of Mankato, said Erika Butler, a DNR wildlife veterinarian. Test results are pending, but DNR officials believe the cause is Newcastle disease, a virus that is spread by droppings and body fluids. Butler described "stereotypical presentation" among diseased birds, including paralysis, drooping heads and the inability to walk or swim. Diseased birds were being euthanized; other carcasses were being quickly cleared and incinerated to prevent the spread.
As of last week, DNR officials had discovered 700 cormorants, 100 pelicans and smaller numbers of the other birds dead and diseased at Pigeon Lake. The toll amounted to fewer than 100 at Minnesota Lake.
Butler noted that the dead birds tested negative for avian influenza.
This year's Newcastle outbreak, which is smaller than those reported previously, is not exacerbated by climate conditions; the biennial outbreaks more likely have to do with the way immunity is passed from bird to chick, Butler said. The disease does tend to strike juvenile birds hardest. This year's relatively lower numbers could be the happy result of an early spring, she said; many juveniles already have grown enough to leave their colonies. It's not clear why the virus hits cormorants so hard, she said, but she added that even such a large die-off will not have a big effect on the statewide population, which has been healthy.
The disease also tends to revisit the same lakes, she said, likely because of preexisting colonies there.
Bird die-offs also have been reported this summer on Leech Lake, Lake Vermilion and the Canadian side of Rainy Lake. Test results are pending in those cases also. In 2008 and 2010, several thousand birds died in Newcastle outbreaks across the state. A 1992 outbreak killed 35,000 double-crested cormorants across the Great Lakes, Upper Midwest and Canada, according to the DNR.
The disease rarely spreads to humans, the DNR statement said. Symptoms in humans can include conjunctivitis, a mild inflammation of the inner eyelids also known as pink eye. It can spread to domesticated flocks; owners should block wild birds from their chicken pens and monitor them for illness.
Maria Elena Baca • 612-673-4409