Recovering from the brink in Michigan, eagles still face threats
Bald eagles have recovered from the brink of extinction in Michigan but still face death from a few unusual circumstances.
The soaring scavenger birds die more now from trauma after being struck by cars and from the lead they consume as they pick off the carcass of road kill and animals like deer, according to a recent study in the Journal of Wildlife Management.
Necropsy data from 1986 to 2017 show that bald eagles still are dying, but not in alarming numbers. The study, by biologist Kendall Simon who now works for the U.S. Fish and Wildlife Service, focused on 1,490 dead bald eagles.
After decades of a decline, Michigan has an estimated 2,500 bald eagles, including more than 500 young eagles that aren't of breeding age, experts said.
Bald eagles were one of the first species to receive protections under the precursor to the Endangered Species Act in 1967, according to the U.S. Fish and Wildlife Service. They were removed from the Federal List of Endangered and Threatened Wildlife and Plants in 2007.
Marvin Roberson, a forest ecologist for the Michigan Sierra Club, said he is not surprised that vehicle mortality was the leading cause of death for the birds of prey.
"Bald eagles are scavengers, and road kill is a favorite form of food for them because they are sitting on the road," Roberson said. "Unlike a lot of smaller birds who can fly off when they see a car coming, it takes a bald eagle a ways to get the engine running and off the road. If somebody doesn't slow down, it's not like a sparrow who just speeds off into the distance."
Simon, who originally is from Portland, Michigan, but wrote her paper for her PhD at the University of Maryland, said the switching of food from fish to road kill is one of the causes of death.
"There's a gradual, not a significant, upward trend (in deaths) and that is a functional response to the increasing population," Simon said. "Eagles like to live on water. They prefer to eat fish. If they can't fish, they definitely eat a deer on the side of the road."
The majority of the deaths were females, who are the larger bird among the gender, Simon said.
Simon said as the population increases in ideal eagle breeding territories along waterways, new, inexperienced eagles are forced to settle in lower-quality habitats that don't have access to water.
Behind the risk of getting struck by vehicles, eagles "who love an easy meal" become victims of consuming lead in carcasses of animals shot by hunters.
Their resurgence can be attributed to the banning of contaminants like PCBs and the decrease in eggshell thinning. There are now close to 900 breeding pairs in Michigan, Simon said.
"They've made a pretty dramatic comeback," she said.
Ed Golder, spokesman for the Michigan Department of Natural Resources, said the department recommends "the use of non-lead shot and bullets, so we encourage voluntary hunter support for reducing potential lead poisoning in eagles."
Golder also recommends keeping a watchful eye for the majestic birds on roadways.
"As the study shows, vehicle strikes are a primary cause of bald eagle deaths in the state," he said. "That’s a good reminder to motorists to be on the lookout for eagles feeding on the side of the road, to slow down when they see one, and to make room by changing lanes, if they are able, in order to prevent hitting birds when they take off because of passing cars."
Simon said she found a "disproportional increase" in deaths due to vehicular trauma and lead poisoning in recent years in comparison to the first couple of years of the study.
The Sierra Club's Roberson said that despite the deaths, he sees a silver lining in the data: there are more eagles.
"The fact that there enough bald eagles eating roadkill to be killed by cars is actually a good sign," he said. "Forty years ago, there weren't enough bald eagles hanging around. Seeing one was a big deal. While it's a tragedy individually, it's a sign that the population has rebounded enough that this is actually a concern."
Simon said the fate of bald eagles also can affect other scavenger species such as crows, turkey vultures and coyotes.
In her study, Simon suggests ways to save the birds of prey.
"We recommend moving road‐killed carcasses, especially white‐tailed deer, from the main thoroughfare to the back of the right‐of‐way, and the transition from lead
ammunition and fishing tackle to non‐toxic alternatives to decrease these main anthropogenic sources of mortality for bald eagles, and other scavenger species," Simon said in her study.