This is a compelling story of mysterious bird deaths that is raising concern for the health of eagles, ducks
geese and fish in the southeastern reservoirs.
It all started in DeGray Lake, Arkansas, where 69 eagles died over the course of three winters from 1994-1996. Wildlife biologists and disease scientists investigated the cause of death and found no known toxins or infectious disease agents at the reservoir or in the birds that died. They did find an interesting and distinct lesion, or tiny holes in specific regions of the brain tissues of the eagles and waterbirds that were found dead at DeGray Lake. Veterinary pathologists from the USGS Wildlife Health Center described the new disease and named it for the lesions they found in the brain—Avian Vacuolar Myelinopathy (AVM).
Since 1994, the disease has been found in 7
states in 18 separate reservoirs, and is considered the cause of death for over 150 eagles and 1000’s of waterbirds. Investigation into the cause of death continues as a collaborative effort between University of Georgia Warnell School of Forestry and Natural Resources, UGA Southeastern Cooperative Wildlife Disease Study, Augusta State University and the Georgia Department of Natural Resources. It has taken a team of scientists from different fields; veterinarians, wildlife biologists, toxicologists, and aquatic ecologists studying the issue together to understand the underlying cause. Many questions still remain, but we have some important clues from reservoir surveys/trials and laboratory experiments.
FIELD OBSERVATIONS: We looked at all the lakes where eagles and waterbirds were diagnosed with AVM and found some important clues.
Clue #1: All the places where birds have died from AVM are on or very near man-made reservoirs in the southeastern United States.
Clue #2: All of the AVM reservoirs have extensive invasive aquatic vegetation, usually hydrilla (Hydrilla verticillata), but also brazilian elodea (Egeria densa) and eurasian milfoil (Myriophyllum spicatum)
Clue #3: An unknown species of blue-green algae (cyanobacteria) was growing densely on the leaves of the invasive plants in all the sites where birds where dying from AVM. Cyanobacteria are known to produce toxins, including neurotoxins, that can harm humans, fish, and wildlife.