The Bald Eagles of Conowingo Hydro Station
By Patrick D Hahn
Propelled by the rapid steady strokes of its long powerful wings, a bald eagle zooms over the tops of trees at the edge of the cliff overlooking the river valley below. The eagle alights on one of the trees for a moment, then takes to the air again, wheeling in a great semi-circle before soaring over the crest and disappearing from view.
I’m walking alongside the Susquehanna River in Harford County, Maryland, just south of Conowingo Hydroelectric Power Station.
The word “Conowingo” is Susquehannock for “at the rapids.” This area was also once known as Smyth’s Falls, after the explorer John Smith, who mapped the region in 1612. The Conowingo Dam supports a 9,000-acre reservoir covering what was once the village of Conowingo, which was ultimately resettled a mile north of the dam to make way for the project. The reservoir provides drinking water for the City of Baltimore and the Chester Water Authority, as well as cooling water for the Peach Bottom Nuclear Generating Station—not to mention habitat for fish and wildlife, and opportunities for boating, fishing, and birdwatching.
The dam itself was built between 1926 and 1928 by the Arundel Corporation, at the behest of the Philadelphia Electric Company. At the time, it was the second-largest hydroelectric power plant in the United States in terms of output, bested only by Niagara Falls. Today, the dam is operated by the Susquehanna Electric Corporation, part of the Exelon Power Corporation. The generators produce power at 13,800 volts, which is stepped up to 220,000 volts for transmission, mostly to the Philadelphia area. The plant is considered a secondary generating facility, providing power only when demand is high. The dam is equipped with 11 turbines with a combined generating capacity of 572 megawatts. When the turbines are running, the intake valves suck in water, and fish, from the reservoir above, spewing them out below—in turn providing a banquet for fish-eating birds. This area is considered one of the best spots in the eastern United States for viewing our national bird, the bald eagle.
My journey begins at Fisherman’s Park, a facility built and maintained by the Exelon Corporation, just south of the dam at the end of Shure’s Landing Road. It’s late morning in late February, four weeks after a record-breaking snowfall. The air is pleasantly cool for now, and temperatures will rise to 60 degrees before the day is done. By now, most of the snow has melted. The few patches that remain have taken on a coarse, grainy texture, speckled with dust and grit.
The dam is a massive concrete edifice, 4,648 feet long and 105 feet high. Its western side is topped by a fantastically ornate steely gray tiara of transformers and God knows what else. Water is churning out of the floodgates, and hundreds of seagulls are circling overhead. To my left and right are several ladies and gentlemen, most of them appearing to be over fifty years of age (as I am), most fiddling with various expensive-looking cameras and binoculars and telescopes, all hoping to catch a glimpse of the largest bird of prey in North America. Adult bald eagles weigh up to fifteen pounds, with wingspans as great as eight feet in length. They can reach speeds of up to 100 miles per hour while dive-bombing prey.
The bald eagle ranges from the Aleutian islands, through Alaska and Canada, to the Labrador and French territories of Saint Pierre and Miquelon, and south through the 48 contiguous United States into northern Mexico. Bald eagles prefer mature forests in undisturbed areas, alongside coasts or the margins of lakes or rivers. They will winter as far north as open water is available, while populations in more northerly areas will fly south for the winter.
More than half of the bald eagle’s diet consists of fish. They also dine on waterbirds, turtles, snakes, frogs, crabs, crayfish, rodents, hares, raccoons, baby seals, and even larger mammals. A bald eagle once was observed carrying away a fawn weighing fifteen pounds, and bald eagles can attack and kill adult deer and pronghorn. They also have been observed preying on domestic sheep and calves, although this is rare. Customarily the eagle makes its kill by stabbing its victim in the back with its razor-sharp talons, closing its digits around the spinal cord and puncturing the aorta. An eagle may also simply seize a young lamb or fawn and begin eating it alive, causing the hapless victim to die by exsanguination. Bald eagles are not averse to carrion, and have been observed dining on dead animals, including beached whales. There is no animal that will prey on an healthy adult bald eagle; they stand at the top of the food chain.
Bald eagles mate for life. Their nests, usually built from 50 to 150 feet above the ground, may be up to thirteen feet across and eight feet deep, and may weigh as much as three tons. The same nest may be used for several years in a row, until it collapses from storms, or the branches supporting it break under its weight. Nest-building or reinforcing usually takes place in mid-February, and one to three eggs are laid in late February. The young hatch from mid-April through early May, and fledge sometime between late June and early July.
The decline and resurgence of the bald eagle population is one of the most resounding success stories in the history of wildlife management. When the first European settlers arrived, the population is believed to have numbered in the hundreds of thousands, but over the centuries that number was cut down and down and down. A variety of factors were responsible, including habitat destruction, legal and illegal hunting, and lead poisoning from lead shot. Another factor was thinning eggshells, which led to eggs breaking before they could hatch. This phenomenon was first observed right after World War Two ended, around the time that DDT and other chlorinated hydrocarbons came into widespread use. Scientists suspected that DDT might be the culprit.
The bald eagle never was in danger of going extinct as a species, but there was a very real possibility of our national symbol disappearing from the lower 48 contiguous states. To some, it appeared the the “silent spring” Rachel Carson had warned us about, in her book of the same title, was upon us. Public outcry from a burgeoning environmental movement, sparked in part by Carson’s book, led the EPA to ban DDT for domestic use in 1972, with some exceptions allowed for public health. Subsequent research confirmed that DDE, a metabolite of DDT, does indeed cause eggshell thinning, in a direct dose-dependent fashion, at least in the American kestrel, a smaller relative of the bald eagle.
It would be remiss not to mention that an entire cottage industry has sprung up, asserting that Carson's admonitions led to the banning of DDT, and in turn 100 million deaths due to malaria. Suffice it to say, here, that Carson, who died in 1962, never called for DDT or any other pesticide to be banned, and there never was a worldwide ban of DDT. The reason some countries stopped using DDT to control mosquitoes was because overuse of that pesticide led to the development of resistance – just as Rachel Carson had warned.
At any rate, in the years subsequent to the EPA ban on DDT, the population of bald eagles in the lower 48 states rebounded dramatically, from a low of 412 breeding pairs in 1963 to over 11,000 breeding pairs by 2007, at which point the bald eagle was removed from the list of threatened and endangered species.
I’ve come to Conowingo Hydro Station to view some of these great birds myself, but I can’t see any. Maybe I could if I owned some of the fancy optical technology deployed by my fellow bird-watchers, but I don’t, so I elect to begin walking along the Lower Susquehanna River Trail, beginning the trail from the south end of the parking lot, to see what I can see there.
To my left is the river itself, which today is pewter-gray in color, muddy and turbulent and swollen by the recent rains. To my right is the remains of the Susquehanna and Tidewater Canal, now long abandoned and largely filled in and overgrown with trees – maples, oaks, sycamores, poplars, and birches. All the leaves have long since turned brown and dropped off, leaving the branches bare, belying the new life waiting to burst forth with the coming of spring. Parts of what used to be the canal are low enough to catch the rainwater in temporary pools, still covered in ice and festooned with duckweed. Beyond that is the side of the river valley, rising up abruptly, almost vertically, forming a high wall, thickly forested and strewn with giant boulders. I am treading on what used to be the canal towpath, now covered in fine gravel to make a comfortable walking surface.
Past the 1.5 mile marker, the sides of the river valley start to recede from the edge of the canal, which is getting a little deeper and becoming more and more recognizable as such. Past the 1.75 mile marker, the trail makes an abrupt 90-degree angle turn to the right and passes over a wooden footbridge straddling the canal. Then it begins following Deer Creek, the largest tributary of the Susquehanna River. Past the 2 mile marker, I come across a 20-foot high stone tower topped with a brick dome. This is the Stafford Flint Furnace. Once upon a time, this tower would be packed with alternating layers of flint and wood which was then set afire, driving the water out of the flint and cracking it into smaller pebbles. These were ground to a fine powder which was washed, bagged, and shipped to Trenton, New Jersey, to be used to make porcelain tableware. This furnace is the only remnant of the once-thriving town of Stafford, which got its start in 1749 with the construction of the Rock Forge, an iron forge built by entrepreneur George Rock. At one time this town boasted forges, furnaces, mills, a boarding house, a school, and a post office. But in 1904, after years of decline, much of the town was destroyed by an ice gorge.
The trail ends at Stafford Road, just beyond the furnace. A solitary bicyclist whizzing past is the only other human being in sight. On the other side of the road is a wooded hillside, part of Susquehanna State Park, damp patches of snow still lingering in the shade of the trees.
It’s time for me to start heading back. I am almost back at the parking lot when the bald eagle comes soaring in overhead. The encounter takes only a few seconds, but there is no doubt as to what I saw. No other bird in North America can possibly be mistaken for an adult bald eagle.
As I settle into the car for the drive home, I take a moment to reflect. If such a magnificent animal can exist in the shadow of a power plant that provides electricity to hundreds of thousands of people, then perhaps the Silent Spring that Rachel Carson prophesied is not our inevitable destiny. Perhaps, little by little, we can learn to live in harmony with nature.
Patrick D Hahn is an Affiliate Professor of Biology at Loyola University Maryland and a freelance writer.