Brian Barton
Eagles are majestic birds of prey that have become a symbol of national pride in the United States. However, these majestic creatures face significant threats from various forms of pollution. Lead poisoning, for instance, has been found to be a major cause of mortality in eagles, with almost half of all American bald and golden eagles suffering from chronic lead poisoning due to the use of lead ammunition by hunters. Additionally, plastic pollution has been found in the stomachs of eagles, causing the deterioration of stomach linings and the production of deadly toxins. Other pollutants, such as bromine, have also been detected in eagles, leading to a disease called avian vacuolar myelinopathy (AVM), which causes physical impairment and often results in death. The impact of pollution on eagle populations highlights the urgent need to address these issues and protect these iconic birds.
| Characteristics | Values |
|---|---|
| Number of eagle deaths from pollution | 70+ in DeGray Lake, Arkansas |
| Type of eagles affected by pollution | Bald eagles, golden eagles |
| Causes of eagle deaths from pollution | Lead poisoning, avian vacuolar myelinopathy (AVM) |
| Factors contributing to lead poisoning in eagles | Use of lead ammunition by hunters, scavenging on animals killed by lead shot |
| Symptoms of AVM in eagles | Poor coordination, stumbling, flying into obstacles |
| Impact of AVM on eagle populations | Mass die-offs, long-term effects on eagle habitats |
| Sources of pollution leading to eagle deaths | Bromine-based herbicides used by lake managers, lead pollution |
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What You'll Learn
Lead poisoning from ammunition
Lead poisoning is a significant cause of eagle deaths. Research has shown that almost half of all American bald and golden eagles suffer from lead poisoning, with 33-35% of eagles suffering from acute lead poisoning and 47% of bald eagles and 46% of golden eagles suffering from chronic lead poisoning.
Eagles are exposed to lead through the ingestion of lead ammunition fragments left in carcasses and offal. Lead ammunition is used by hunters to kill game animals, and when hunters field dress their kill, they leave behind the entrails, which eagles then scavenge. Lead core rifle bullets fragment into hundreds of pieces upon impact, and these fragments can spread far beyond the wound channel, with some found up to 18 inches from the wound site. When eagles consume these fragments, they ingest a potentially deadly meal. Even at very low levels of exposure, eagles show signs of toxicity, including gastrointestinal dysfunction, neurological impairment, depression, seizures, weakness, and death.
The use of lead ammunition has been linked to the widespread lead poisoning of eagles and other wildlife. Lead is a potent toxin that can have serious ecological and human health consequences. Lead ammunition has been banned for hunting waterfowl since 1991 due to ducks and other aquatic species dying after consuming lead shot. However, it is still permitted for hunting upland game birds, deer, elk, and nuisance animals in some states.
To reduce the risk of lead exposure to eagles, conservationists advocate for the use of non-lead ammunition. There are many effective, non-lead alternatives to lead-based ammunition, with more options becoming available each year. Transitioning to non-lead ammunition eliminates the exposure of eagles and other wildlife to lead toxicity and also results in a safer food source for humans.
While lead poisoning from ammunition is a significant issue, other sources of lead exposure for eagles include lead fishing tackle and lead in the environment from historical uses, such as in paint and plumbing.
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Avian vacuolar myelinopathy (AVM)
The cause of AVM eluded scientists for decades, but it is now known that the disease is caused by a neurotoxin called aetokthonotoxin produced by cyanobacteria. Specifically, the cyanobacterium Aetokthonos hydrillicola colonizes an invasive plant, Hydrilla verticillata, which grows in man-made water bodies. The neurotoxin is produced when this invasive plant is colonized by the cyanobacterium. Field and laboratory studies have demonstrated that AVM can be transferred up the food chain, affecting not only waterbirds but also birds of prey that consume affected waterfowl.
The occurrence of AVM has been linked to the use of bromine-based herbicides by lake managers to control the invasive weed H. verticillata. Bromine is a chemical element that is rarely found in nature, particularly in freshwater. Instead, it is usually introduced by human activities, such as the use of pesticides, dyes, gasoline, and plastic casings for electronics. Scientists are still working to understand the factors that affect the distribution and toxicity of invasive aquatic plants and the sources of bromine in the environment.
Since its discovery in 1994, AVM has spread to four more states in the southeastern United States and infested multiple aquatic systems, including 10 reservoirs. The disease has been documented in numerous avian species, most notably waterbirds such as American coots, ring-necked ducks, mallards, and Canada geese, and in various birds of prey. In addition to avian species, AVM has also been found to affect amphibians, reptiles, and fish. Active surveillance during outbreaks at Clarks Hill/Strom Thurmond Lake on the Georgia/South Carolina border from 1998 to 2004 yielded annual average prevalences of vacuolar lesions in 17-94% of coots.
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Plastic pollution
Bald eagles, a symbol of the United States, are vulnerable to plastic pollution due to their diet consisting largely of fish. Research has revealed the presence of microplastics in numerous fish species, which then accumulate in the eagles that consume them. This contamination extends beyond the eagles, as they themselves become part of the food chain, passing on the toxic effects to their predators.
The impact of plastic pollution on eagles is not limited to those that inhabit aquatic environments. Landbirds, including eagles, are also affected by plastic waste. This is due to the widespread presence of plastic in the environment, which can be easily spread by wind and waves, reaching even remote areas.
Addressing plastic pollution is crucial to mitigating its harmful effects on eagles and other wildlife. Efforts are being made globally to reduce plastic waste and improve recycling practices. Campaigns such as the Clean Seas campaign by UN Environment aim to raise awareness and encourage individuals, governments, and businesses to take concrete steps to reduce their plastic footprints.
In conclusion, plastic pollution poses a significant threat to eagles and other bird species. The ingestion of plastic and its associated contaminants can lead to severe health issues and even death. By understanding the detrimental effects of plastic pollution on eagles, we can emphasize the urgency of addressing this global issue and work towards protecting these majestic birds and the delicate balance of our ecosystems.
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Bromine-based herbicides
While there is no direct mention of bromine-based herbicides being responsible for eagle deaths, bromine is a chemical element that can indicate pollution when found in the environment. Bromine is scarcely found in freshwater but is often introduced into nature through human-caused products such as pesticides, dyes, gasoline, and plastic casings for electronics.
In 2022, scientists discovered that bromine-based herbicides used to control the invasive weed H. verticillata may have caused the deaths of eagles in DeGray Lake, Arkansas, in 1994. This was due to a disease called avian vacuolar myelinopathy (AVM), which causes significant physical impairment and often leads to drowning, starvation, or injury. The cause of AVM eluded scientists for decades, but they eventually discovered that cyanobacteria produced toxins due to the bromine-based herbicides used by lake managers.
Additionally, methyl bromide (bromomethane), an organobromine compound, has been widely used as a pesticide and is recognized as an ozone-depleting chemical. While most countries have phased out its use, it is still preferred by some agricultural departments for fumigating organic goods. Methyl bromide is toxic to humans and has been linked to respiratory, kidney, and neurological issues.
Overall, while bromine-based herbicides may have contributed to eagle deaths in specific cases, other pollutants such as lead poisoning and methyl bromide also pose significant threats to eagle populations.
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Trauma and electrocution
Trauma in eagles can be caused by collisions with vehicles, wind turbines, power lines, trains, and other objects. Natural features, such as trees or rocks, can also cause trauma, although this is less common. Eagles may also suffer trauma from predation or fighting with other eagles.
Electrocution is often caused by power lines. As eagles are large birds with a significant wingspan, they can easily touch two power lines simultaneously or a power line and the ground, completing an electrical circuit and receiving a fatal electric shock.
In addition to immediate deaths caused by trauma and electrocution, these incidents can also cause injuries that lead to secondary causes of death, such as drowning, infection, or starvation.
While the number of eagle deaths caused specifically by trauma and electrocution is challenging to determine, studies have shown that these factors contribute significantly to eagle mortality.
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Frequently asked questions
Eagles can be poisoned by lead ammunition used by hunters. When they scavenge on animals killed by lead shot, they can consume the metal. Eagles also accumulate hazardous waste through their meals as fish make up a significant portion of their diet.
Lead poisoning causes poor coordination while walking, swimming, and flying. The eagles may also act strangely, such as flying straight into cliff faces or stumbling around as if drunk.
Almost half of all American bald and golden eagles are being poisoned by lead.
