Betty Thompson and her husband Tim, both former Knoxvillians, were visiting Columbia Bottom Conservation Area outside of St. Louis in the spring of 2021. Betty is an avid bird photographer and always is on watch.
“I saw his white head in a grassy area. He was on a low embankment about 20-30 feet from us. I was excited and camera ready. At first I thought he might be sitting on some prey. However, as we stopped roadside he didn’t fly away,” Betty remembers.
“He looked healthy, I did not notice any injuries to his wings, but I knew it was odd that he stayed. When I approached he attempted to fly. He only made it a few feet in the air and several feet in distance. After two poor attempts at flying he landed roadside.”
The Thompsons drove away but eventually came back to that same road and saw the downed eagle was still there. It was still in distress and they reported it to park staff.
After returning home to Kansas they learned via email that the eagle was suffering from lead toxicity and had later died.
Eagles are majestic hunters. They primarily eat freshly caught fish. But they also scavenge and will occasionally eat carrion that contains a hunter’s lead bullet or pellet. A piece of lead the size of a grain of rice will be enough to eventually kill the bird. But it is not only eagles. The American Bird Conservancy estimates 16 million birds die of lead poisoning every year by accidentally ingesting it through eating carrion or spent shotgun pellets mistaken for seeds by birds like mourning doves. Hunters are asked to switch to non-lead ammo.
Symptoms of lead toxicity in birds can include panting, confusion and poor muscle control. The bird may appear drunk and bewildered. Despite this, if they are found and taken to a veterinary in time they can be saved.
“Ingested lead quickly becomes absorbed and high levels can occur quickly. Lead in tissues from being shot results in a slow absorption of lead depending on exactly which tissues are involved,” said Dr. Cheryl Greenacre, DVM at the University of Tennessee College of Veterinary Medicine.
“Lead toxicity is treated with a drug called Calcium EDTA, a binding agent or chelator that bonds with the lead in the blood and the bird urinates it out. It cannot bind lead stored in the bone, so treatment may be prolonged in severe cases, but the disease is usually treatable if we get the animal in time.”
Lead poisoning has occurred for a while. California condors almost went extinct as a result. From a low of only 22 birds in the 1980s, they are now up to about 300 but it has taking a lot of effort to lift the population to that number.
Lead poisoning was partly to blame for the condor’s collapse and is still the leading cause of their deaths. The scavengers live on carrion and ingest lead from the remains of animals killed with lead ammunition.
A new threat to eagles
There is also a mysterious “new” disease that has killed dozens and perhaps hundreds of eagles across the country. Diagnosed as Avian vacuolar myelinopathy (VM), it was first discovered in 1994 when a large number of bald eagle carcasses were found near DeGray Lake in Arkansas and has now been reported as being responsible for eagle deaths in nine states from Virginia to Texas.
VM is only found in lakes where hydrilla verticillata, an invasive plant from Central Africa, is also found. It has taken 25 years to unravel how this disease works. Early in 2021 it was reported that the deaths were apparently caused by a neurotoxin created by cyanobacteria found in that invasive plant. Here is the kicker: The toxin is called aetokthonotoxin, which literally means “poison that kills the eagle.”
The neurotoxin is only produced if the lake or waterway also has the presence of a high level of bromide.
It gets more complicated
“Bromide does occur naturally in lakes in small doses, but it is also introduced by humans in the form of herbicides (ironically used to control the spread of the hydrilla), as well as chemical run-off from both flame retardants and pollution from coal-powered power stations,” wrote doctoral student Steffen Breinlinger.
Here’s another kick in the keister. How did hydrilla verticillata get to our shores? Beginning in the 1950s it was imported as a popular plant for home aquariums because it stays lush and green under low artificial light. But when that hobby became tiresome, the aquarium’s contents were often dumped in nearby ponds or lakes, where Hydrilla spreads like kudzu.
“Hydrilla verticillata is one of the most serious and troublesome aquatic weeds in the world’s waterways. Its massive spread is largely due to human activities, such as boating and fishing and the aquarium trade,” wrote J.L. Scher for the USDA.
As Walt Kelly’s Pogo Possum observed in 1971 while looking at a swamp full of trash: “Son. We have met the enemy and he is us.”
Stephen Lyn Bales is a natural historian, the author of three UT Press books: Natural Histories, Ephemeral by Nature, Ghost Birds.” He’s also a monthly speaker (via Zoom) for the UT Arboretum Society. He can be reached via email to “stephenlynbales” at gmail.com