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Pennsylvania's bald eagle population rebounded from near extinction thanks to federal protections, a ban on DDT and 88 eaglets from Saskatchewan, Canada.
There are at least three bald eagle nests within driving distance of Philadelphia. Two others are located near West Chester, Pennsylvania, and one near Lancaster; a handful surrounding Pittsburgh and dozens lining Lake Clarke, which runs between York and Lancaster.
Throughout Pennsylvania, there are more than 300 nesting pairs of bald eagles, according to estimates from the state’s Game Commission—so many that officials rely on help from the public to count them. It’s a complete turnaround from the early 1980s, when state populations of the bird had dropped to just three nesting pairs, prompting wildlife officials to hatch a conservation plan that relied on a little help from Canada.
“It was a multi-state approach to bring birds from other parts of North America into the Northeast and boost the population quickly,” Patti Barber, an endangered bird specialist with the Pennsylvania Game Commission, said in a video about the species. “About 88 birds were brought from Saskatchewan and were raised in Pennsylvania through a process called hacking.”
Hacking, in avian parlance, is a process where young birds (typically nestlings) are raised in controlled environments without being able to see their human caretakers. This prevents them from imprinting on people or equating humans with food, which allows the birds to be released into the wild at the age where they would normally leave the nest on their own.
The program worked, and it worked relatively quickly. In 1998, 25 adult pairs of eagles were reported to the Game Commission, which increased to 100 in 2006 and more than 300 today. Those results were aided by several factors, including federal protections for both endangered species and bald eagles specifically, along with a nationwide ban of DDT, a pesticide that wreaked havoc on wildlife across the country.
“DDT would enter the environment and it bioaccumulates, so say a small fish gets some of the pesticide in their system,” said Sean Murphy, Pennsylvania’s state ornithologist. “A bigger fish is going to eat a lot of small fish, and when that kind of trophic transfer happens, it’s the top predators that end up being impacted because they’re accumulating all of what’s been concentrated as it moves up the food chain.”
When ingested by adult eagles, DDT caused eggshells to thin, either preventing a viable embryo from forming or causing the egg to crumble under the weight of its parents. The pesticide was outlawed in 1972, and it slowly flushed out of the ecosystem in the years after, which eventually eliminated its impacts on the bald eagle population.
The bald eagle’s natural tendencies also worked in its favor, Murphy said. Though the bird dines primarily on fish, it will scavenge when necessary, picking at roadkill and even stealing food directly from other birds.
“When you look at species at the broad scale, typically if you’re kind of an opportunistic forager you tend to be pretty successful, and I think that helped in their recovery,” he said. “They’re good at what they do, and when we provided them protection the population was able to recover, and their biology certainly helped in that.”
The species was delisted as federally endangered in 2011 and downgraded to protected at the state level in Pennsylvania in 2014 (although they are still covered by the federal Bald and Golden Eagle Protection Act). The state ceased nest-by-nest monitoring at that point, but officials wanted to continue to keep an eye on population levels so they’d know if conditions changed.
They decided to turn to the public for help, launching a web tool in 2018 that allows birdwatchers and eagle enthusiasts to plot their sightings on a map. The site asks residents for details of the encounter, including the behavior they observed (nest-building, incubating, chick-rearing) and the number of eagles spotted. The resulting data is streamlined by state officials and sent to the U.S. Fish and Wildlife Service, which uses the information to ensure that nests are being appropriately protected as required by federal guidelines.
“The impetus for the bald eagle tool started with the fact that everyone loves bald eagles and likes to talk about them,” Murphy said. “But it provides valuable information as well. Once people put those data into the tool, it marks a nest as active, which grants it five years of protection. It’s great for identifying new nests, and all indications we have are that the population is still increasing.”
That information is useful to the state, both for monitoring purposes and for conservation efforts. The bald eagle’s turnaround is a rare success story, and state officials like to promote it, Murphy said.
“Everybody knows a bald eagle—it’s the national bird and it has all this heritage attached to it, and now they’re pretty much everywhere throughout the state,” he said. “Wherever you are, it’s a great point to connect with folks when you want to talk about wildlife or deliver the message of conservation. It’s just a great tool to connect with the public.”
Kate Elizabeth Queram is a Staff Correspondent for Route Fifty and is based in Washington, D.C.