More S.C. bald eagles fall to brain disease

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More S.C. bald eagles fall to brain disease

Saturday, February 16, 2002

BY LYNNE LANGLEY

Of The Post and Courier Staff

More of South Carolina's nesting bald eagles have died this year from a

neurological disease, now thought to be caused by a toxic alga growing on

the common aquatic plant hydrilla.

Biologists have picked up six more dead eagles at Lake Strom Thurmond,

where nesting has plummeted from 11 territories to one in just two years,

according to Tom , S.C. Natural Resources Department eagle specialist.

" We could start seeing massive mortality, " said.

" This is alarming, " Holliday told fellow members of the Natural

Resources Board, which met Friday in ton.

" It's a scary situation. We know the prevalence of hydrilla, " said

McTeer, deputy director of Wildlife and Freshwater Fisheries.

Avian Vacuolar Myelinopathy, which breaks down the central nervous

system and causes brain lesions, was first diagnosed in Arkansas in the

winter of 1994-95 and in South Carolina four years later. The disease has

been confirmed every year since at four South Carolina reservoirs: Lake

Thurmond, Lake Murray and Par Pond and L Lake on the Savannah River Site,

said.

The disease, diagnosed on 11 reservoirs in five Southeastern states,

has only been found on inland, man-made reservoirs low in nutrients, not

along the coast.

Reservoirs cover 521,737 acres in this state compared with 504,445

acres of coastal marshlands. Eagles, which once used only those coastal

sites, increasingly have spread to inland reservoirs.

Between 150 and 200 eagles use South Carolina reservoirs, and 52

breeding pairs are known to nest on the largest ones, according to .

Statewide, 162 pairs produced young in this state last winter.

It is now believed, but not proven, that AVM is caused by a naturally

occurring biotoxin produced by an alga species, said, adding that the

most likely suspect is a blue-green alga that grows on hydrilla.

That alga has been found in every reservoir where AVM has affected

birds such as eagles and coots and in no bodies of water where the disease

has not been confirmed, he said.

Hydrilla grows widely across the Southeast. Department aquatic nuisance

species manager de Kozlowski expects the non-native plant, which can

cover up to 4,000 acres in one year, will spread into every reservoir in the

state before long.

" It could take half the eagle territories in South Carolina, "

said.

At first, the disease appeared to be killing northern eagles that spend

the winter here, but now local nesters are dying.

This winter, 10 of the 11 nest sites at Lake Thurmond and both nests on

the Savannah River Site reservoirs sit empty, meaning that both eagles in

the pair have died, said. Normally he expects to lose less than 2

percent of established territories in a year.

He described the loss as catastrophic locally. As for a larger regional

effect, he said, " The potential has us all edgy now. "

Eagles appear to pick up the disease by eating sick coots, which feed

on algae.

When a disabled coot can no longer fly, swim or dive normally, it

becomes a magnet for eagles, said.

A bird develops symptoms five days after being introduced to an AVM

site and is dead within seven days. Of SRS coots sampled last year, 95

percent had brain lesions even if they didn't show symptoms.

Sick coots on reservoirs that didn't contain hydrilla had the plant in

their stomachs, indicating that coots could carry a death warrant with them,

and eagles could die.

" We wouldn't know, " said.

So far, eight species of birds ranging from waterfowl to great horned

owls to killdeer have been confirmed as victims of AVM, but it has not been

found in mammals or fish.