Determine the Age of a Golden Eagle in Flight—Well, Maybe
The Golden Eagle (Aquila chrysaetos), a majestic Holarctic raptor of remote mountains, plains, prairies, and deserts, is a species that is both revered and persecuted by human cultures. By some societies and civilizations, it has been highly regarded and, in some cases, worshiped as a symbol of courage, strength, power, and mysticism. For hundreds of years, its likeness has been crafted into the shields, seals, banners, and statuary of numerous nations and empires. In North America, this eagle’s feathers are those often used to adorn ceremonial tribal headdresses. Unfortunately though, as a living entity, the species suffers many of the worst fates man can dish out. It is shot, trapped, imprisoned, bludgeoned, poisoned, electrocuted, and most recently, “wind turbined” to death. The Golden Eagle doesn’t fare well when man moves into the neighborhood.
Herbert H. Beck, in his 1924 publication, A Chapter on the Ornithology of Lancaster County, Pennsylvania, cites Dr. M. W. Raub:
“Prior to 1850 a pair had their eyrie on a cliffside of the Susquehanna opposite the mouth of the Pequea.”
Referring to this same York County nest site, Beck quotes Witmer Stone:
“This was probably the last stand of the golden eagle in Eastern North America.”
Well, it appears not—but we know they were being exterminated wherever people happened to be free-ranging livestock as if it were live bait for birds of prey and other indigenous predators. During the onslaught of European settlement and thereafter, native animals that were just trying to survive the obliteration of their habitats and food chains were mercilessly murdered if they wandered anywhere near man’s realm. Judge J. J. Libhart of Marietta, Pennsylvania, in his 1869 account of Lancaster County ornithology, related Professor S. S. Rathvon’s story of the demise of a Golden Eagle he received into the collection of the Linnaean Society of Lancaster City and County:
“The splendid specimen in the collection of the Lancaster Linnaean Society, No. 124, was shot December, 27th, 1867, near Willow Street in this county, where he had been depredating upon the poultry of the farmers for several weeks. Although fatally wounded, he bravely, while life remained, defended himself against the efforts of his captor to dispatch him.”
Oh my goodness—a heroic man saving the innocent country folk (and poultry) from an evil indestructible villain—a bird. The poor fella with a gun barely escaped with his life! It was pathetic enough then, but can you believe we’re still expected to believe adolescent tales of adventure like this from the grown men of today? Don’t fall for it. It has nothing to do with specimen collecting, predator-prey population balance, protecting chickens, or rescuing goldfish from a heron that raids a garden pond. Just like it was a century and a half ago, it’s all about the adrenaline rush and simplistic satisfaction of blasting the living snot out of something.
Despite the stomping from an ever-expanding human footprint, Golden Eagles in western North America continue to be numerous. Because they travel many miles to retrieve food for young in the nest, large tracts of undisturbed habitat are necessary for the birds to be successful. The vast lands of the North American west can still satisfy this requirement. “Western Golden Eagles” probably number in the tens of thousands.
The “Eastern Golden Eagle”, the other population of the single North American subspecies Aquila chrysaetos canadensis, nests in remote regions of northeastern Canada and winters in the Appalachian Mountains of the United States. They are far fewer in number than their western counterparts—the eastern population probably totaling only a couple of thousand birds. Migrating “Eastern Golden Eagles” are seen each autumn from hawk watch sites atop ridges in the Mid-Atlantic states. Recently, “Eastern Golden Eagles” have become more frequent as wintering birds on the Atlantic Coastal Plain, particularly on the Delmarva Peninsula and in upper Chesapeake Bay. On the Piedmont, they are occasionally spotted among the scores of Bald Eagles (Haliaeetus leucocephalus) that gather annually beginning in November on the lower Susquehanna River in the vicinity of Conowingo Dam near Rising Sun, Maryland. Pennsylvania’s Middle Creek Wildlife Management Area in Lancaster and Lebanon Counties has hosted a wintering Golden Eagle in recent years. Birds headed to these lowlands seem to ignore the benefits of ridge-top flight and can be seen migrating along rivers, coastlines, and even passing over urban and suburban areas to reach their winter retreats.
In the Lower Susquehanna River Watershed, autumn flights of migrating “Eastern Golden Eagles” peak during the last days of October and first two weeks of November. The high count for the season often occurs following passage of a significant cold front on a day with strong northwest winds. In the Piedmont and the Ridge and Valley Provinces, the updrafts created as these winds strike the numerous ridges provide lift and easy flying for eagles headed southwestward toward wintering grounds in the southern Appalachians.
Atop these ridges, the hardiest of raptor enthusiasts gather at hawk watch sites and wait patiently for a chance to observe, count, and study “Eastern Golden Eagles” and other migratory birds.
Waggoner’s Gap Hawk Watch on Blue Mountain north of Carlisle and Second Mountain Hawk Watch at Fort Indiantown Gap are staffed by official counters who record migration data throughout the autumn season. “Eastern Golden Eagle” numbers at Waggoner’s Gap are seldom exceeded by any other census location in the lower Susquehanna region. Just to the northeast of Waggoner’s Gap, the lookout on Cove Mountain offers opportunities to observe eagle passage, but no official count is currently conducted there.
Just to the east of the Susquehanna valley, world renowned Hawk Mountain Sanctuary has been tracking autumn hawk migration at their lookouts since the poachers were evicted in 1934. During that first year, curator of the new refuge, Maurice Broun, discovered the previously unknown southbound movements of “Eastern Golden Eagles” along the ridges of the Appalachians. With only partial coverage during that first season, he spotted more than thirty. By the following year, skeptical ornithologists were coming to see this phenomenon for themselves—among them, Herbert H. Beck. He commented to Broun, “I have travelled thousands of miles to see golden eagles, with never any luck until this day.” Beck was within sixty miles of his Lancaster County home when he saw his first Golden Eagle at Hawk Mountain. Broun would count a total of sixty-six Golden Eagles there during 1935, the first year with complete coverage of the autumn season. Hawk Mountain’s fall migration count has been conducted continuously since 1934, except during the three years of World War II (1943-1945) when Maurice Broun was in military service.
Though not recently in use, the Route 183 Hawk Watch atop Blue Mountain is another excellent location for observing the movement of migrating eagles. It lies just to the east of the Susquehanna watershed about half the distance from Hawk Mountain to the Second Mountain Hawk Watch.
In the lower Susquehanna valley, numerous observation points in the Piedmont Province offer chances for viewing migrating “Eastern Golden Eagles”, but seasonal numbers are a fraction of the concentrations tallied along Blue Mountain and other significant ridges to the north. Governor Dick Fire Tower in Mount Gretna, Conewago Falls on the Susquehanna River, and Rocky Ridge County Park northeast of York are among the locations in the Piedmont Province where they occur annually.
Places to Observe “Eastern Golden Eagle” Migration
- Waggoner’s Gap Hawk Watch (Staffed by Official Counters)
- Second Mountain Hawk Watch (Staffed by Official Counters)
- Hawk Mountain Sanctuary (Staffed by Official Counters)
- Cove Mountain Hawk Watch
- Route 183-Blue Mountain Hawk Watch
- Governor Dick Fire Tower
- Conewago Falls
- Rocky Ridge County Park Hawk Watch (Staffed by Official Counters)
Each of these locations can provide spectacular sighting experiences, but the core of the “Eastern Golden Eagle” flyway through the Susquehanna valley is in the more mountainous region to the west and northwest of the area shown in the image. At hawk watches along the slope of the Allegheny Plateau and its nearest ridges, official counters tally dozens of birds on an ideal day.
Allegheny Front Hawk Watch on Pennsylvania’s Somerset/Bedford County line is located atop the Eastern Continental Divide—rain falling to its east entering first the Juniata River, then the Susquehanna River on its way to the Atlantic Ocean, and that falling to its west making its way to the Gulf of Mexico via the Mississippi River system. This hawk watch is staffed in autumn and in the spring from mid-February through early May. Because the face of the plateau lies along a north to south axis, Allegheny Front experiences its best flights when updrafts are at their best—during days with winds from the east.
Staffed full-time for the first time during the autumn of 2019, Eagle Field on Bald Eagle Mountain northwest of State College documented a fabulous “Eastern Golden Eagle” flight— more than 340 birds. There were nine days in November with ten or more birds counted, including days in mid-month with 24 (twice), 39, 45, 46, and 52! If numbers like this are an annual occurrence, then observers at this site may be seeing the passage of 10% or more of the entire “Eastern Golden Eagle” population each autumn. Perhaps the eagles transiting Eagle Field should be studied more closely.
There are additional locations that offer opportunities to see migrating “Eastern Golden Eagles” in the Ridge and Valley Province in the State College area. In spring, observers at the Tussey Mountain Hawk Watch witness a peak northbound movement in mid-March each year. Counters also tally birds at Tussey Mountain during the autumn. Not far away, on the northwest side of the Kishacoquillas Valley, Stone Mountain experiences good fall flights on north or northwest winds. On the southeast side of the valley, Jack’s Mountain is one of the few sites to experience good autumn flights on a day with southeast winds.
Live in New York state and want to have a look at “Eastern Golden Eagles” migrating through the upper Susquehanna valley? You’re in luck. The Franklin Mountain Hawk Watch on the western edge of the Catskill Mountains is on the south side of the Susquehanna River at Oneonta, New York. The lookout is staffed through the autumn season.
You can view the daily count totals and archived records from hawk watches all over the continent by visiting the Hawk Migration Association of North America’s hawkcount.org. The page also provides a description of each lookout and directions for getting there.
Now, let’s take a closer look at all of those eagles you’re seeing.
This page is specifically designed for the dedicated counters and observers who brave the cold winds of October, November, and December to census Golden Eagles and other late-season autumn migrants from North American hawk watch lookouts.
Counters who staff official hawk watch stations diligently enumerate the eagles, hawks, falcons, vultures, and other migrating birds they see. They record data, hour by hour, for the duration of autumn season. Many counters make a note of the age and/or gender of the rarer species. Golden Eagles, which take five years to attain full adult (Basic V) plumage, can present a real challenge to those tasked with determining the age of a passing bird.
While field observation and fleeting glimpses of eagles in flight can never match the precision that bird banders (ringers) attain by aging a bird in the hand, a hawk watcher can still use some of the same plumage attributes that banders use to accurately determine the age, or age range, of many of the Golden Eagles seen migrating past a given lookout.
Whether you’re an official counter or just a casual observer, the “Golden Eagle Field Observation Log with Aging Key” can help you systematically narrow down the age of a bird that passes by your lookout—even one that provides only a limited view of the aging characteristics. On the log, you enter your sighting data along with the answers to four specific questions for each of your eagle observations. These four questions compel the observer to concentrate study of a passing bird on the field marks that are both critical to determining the bird’s age and readily visible on most birds in flight. By referencing the “aging key” on the log, the answers to these questions can be used to assign each bird you’ve seen to an age class. Age to the exact year can be determined for some eagles, while others can be assigned to one of a number of age ranges spanning up to four years or more.
Use of the “Golden Eagle Field Observation Log and Aging Key” could facilitate development of a more valuable data set for assessing the age classes comprising a population of migrating Golden Eagles seen from one or more given census points. At the very least, it helps to enhance the experience of watching and appreciating migratory Golden Eagles.
Before you begin, you’ll want to read Jerry Liguori’s “How to Age Golden Eagles: Techniques for Birds Observed in Flight”, published in Birding magazine in 2004 (Volume 36, Pages 278-283). You can find it online. This article, and to a lesser degree the literature listed in the sources at the bottom of this page, are the basis for the aging key.
You’ll also want to be familiar with the some of the terms used to describe a diurnal raptor’s plumage, particularly the flight feathers…
TOPOGRAPHY OF A DIURNAL RAPTOR IN FLIGHT
Then you’re ready to begin…
Answer these four questions about the Golden Eagle you’re studying, then enter your responses below the green headings on the observation log:
Question #1: Is there a tawny bar on top of the wings created by lighter-colored median secondary upperwing coverts?
Question #2: Is there evidence of molt in the juvenile remiges (primary and secondary flight feathers in the wings)?
Question #3: Do the undersides of the wings have a two-toned appearance similar to a Turkey Vulture (Cathartes aura)?
Question #4: Is white visible in the rectrices (the long tail feathers)? In addition, note the view obtained of the tail (top, bottom, or lateral), and whether the tail was seen folded or spread.
Enter the date, time, and flight information for your sighting in the appropriate boxes below the blue headings on the observation log.
Consult the aging key to determine the age class of the eagle you’ve studied, then enter its age class code in the yellow box on the observation log with your other data.
Congratulations—you’ve systematically determined the approximate age of a Golden Eagle based upon field observation!
INTERPRETING YOUR RESULTS
NOTE: The term sub-adult, here applied only to a fifth-year Golden Eagle, is sometimes applied to birds in their second through fifth years, and on occasion includes first-year/juvenile Golden Eagles as well.
More to follow on this topic soon.
Beck, Herbert H. 1924. A Chapter on the Ornithology of Lancaster County, Pennsylvania. The Lewis Historical Publishing Company. New York, NY.
Bloom, P. H. and W. S. Clark. 2001. “Molt and Sequence of Plumages of Golden Eagles and a Technique for In-hand Ageing”. North American Bird Bander. 26: pp.97-116.
Broun, Maurice. 1949. Hawks Aloft: The Story of Hawk Mountain. Dodd, Mead Company. New York, NY.
Dunne, Pete and Kevin T. Karlson. 2016. Birds of Prey: Hawks, Falcons, and Vultures of North America. Houghton Mifflin Harcourt. New York, NY.
Ellis, David H. 2004. “Mottling in the Plumage of Juvenile Golden Eagles”. North American Bird Bander. 29: pp.53-58.
Jollie, M. 1947. “Plumage Changes in the Golden Eagle”. Auk. 64: pp.549-576.
Libhart, John J. 1869. “Ornithology”. J. I. Mombert’s An Authentic History of Lancaster County. J. E. Barr and Company. Lancaster, PA.
Liguori, Jerry. 2004. “How to Age Golden Eagles—Techniques for Birds Observed in Flight”. Birding. 36: pp.278-283.