A Natural History of Conewago Falls—The Waters of Three Mile Island
Golden Eagle Aging Chart
Determine the Age of a Golden Eagle in Flight—Well, Maybe
Is this an adult Golden Eagle? Are you sure? Take the guesswork out of determining the age of migrating Golden Eagles by using the “Golden Eagle Field Observation Log with Aging Key”.
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.
Observers search the skies for migrating Eastern Golden Eagles from the lookout at Waggoner’s Gap Hawk Watch on the crest of Blue Mountain north of Carlisle, Pennsylvania.
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 traveled 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.
“Eastern Golden Eagles” are observed each fall at lookouts on the ridge systems of the Lower Susquehanna River Watershed and neighboring Schuylkill River watershed to the east. (NASA Earth Observatory base image)
Places to Observe “Eastern Golden Eagle” Migration
Waggoner’s Gap Hawk Watch (Staffed by Official Counters)*
Second Mountain Hawk Watch (Staffed by Official Counters)*
Route 183-Blue Mountain Hawk Watch (Staffed by Official Counters)*
Hawk Mountain Sanctuary (Staffed by Official Counters)*
Cove Mountain Hawk Watch
Peters Mountain Utility Right-of Ways
Boyd Big Tree Preserve Conservation Area
Governor Dick Fire Tower
Conewago Falls
Rocky Ridge County Park Hawk Watch (Staffed by Official Counters)
Ironville Community Park
* Sites where double digit numbers have been recorded on peak flight days in autumn.
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—in that initial season. Northwest winds produced the biggest numbers. 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 these 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. To more thoroughly assess fall Golden Eagle migration through the Allegheny Plateau escarpment/Bald Eagle Mountain corridor, a nearby observation site, Allegheny Front—Sandy Ridge, was first utilized during the 2024 season as an alternate to Eagle Field on days with wind directions ranging from east to south. The best of these days produced dozens of birds that would not have passed close enough to the Eagle Field site to be counted.
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.
The presence or absence of white in the plumage is, by itself, not a reliable way to assign an age class to a Golden Eagle. While the plumage seen here is typical of a bird before its third year, some birds at this age will have no white at all in the wings and any white in the tail may be indiscernible when it is folded or seen laterally.
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…
Click this image to view, download, and print the “Golden Eagle Field Observation Log with Aging Key” (PDF file). The instructions, consisting of just three steps, are listed at the bottom of the sheet. It includes ten rows for entry of observation data on as many as ten eagle sightings.Expecting more than ten Golden Eagles to pass your lookout today? Lucky you. Here’s a field observation log without the aging key. You’ll have data space for up to twenty-two additional eagle sightings. Click the image to view, download, and print this sheet (PDF file).
STEP ONE
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?
Top View of a Hatch-year/Juvenile (left) and a Second-year/Basic I (right) Golden Eagle- Answer NO to question #1 if there is no tawny bar visible on the top side of the Golden Eagle’s wings (left). Answer YES to question #1 if you observe pale brown median secondary upperwing coverts that create tawny-colored wing bars (right).Even at a distance, the tawny bar parallel to the base of the secondary flight feathers can readily be seen extending along the length of the center of the left wing on this Golden Eagle. Answer YES to question #1 when this bar is seen. Answer NO for birds seen with dark median secondary upperwing coverts.The tawny bars created by pale median secondary upperwing coverts are conspicuous on this Golden Eagle. Note their mottled appearance. Answer YES to question #1 when these bars are seen.With a little luck, an observer may be able to catch a glimpse of the tawny wing bars on a Golden Eagle passing at or near eye level, even while a bird is in powered flight. Answer YES to question #1 when these bars are detected.Tawny wing bars with a mottled appearance on a circling Golden Eagle seen at eye level.The bars on the wings of this second-year (Basic I) Golden Eagle appear as glowing bright-brown smudges, even under marginal lighting conditions. Answer YES to question #1 when these bars are seen. When observing birds similar in appearance to this individual, be careful to discern between the white bases that are present on the juvenile set of primaries and the tawny bars created by the pale median upperwing coverts along the length of the secondaries.The faded median secondary upperwing coverts on this hatch-year (Juvenile) Golden Eagle lack the brighter mottled appearance created by the pale light-brown feathers obtained during a bird’s first molt, early in its second year. Answer NO to question #1 when wing bars are absent or are as indistinct in good light as those seen in this image.Many observers have been led to believe that the absence or presence of white patches in the wings is a key indicator of age, but the lack of tawny wing bars on this Golden Eagle is far and away the more important field mark. Answer NO to question #1 for a bird lacking pale median secondary upperwing coverts like this one and you’ve clinched it!Here, a Golden Eagle displays both tawny wing bars and white on the inner primary feathers. Answer YES to question #1 for a bird like this, but be careful not to confuse the presence of the latter for the former. Look closely and you’ll notice the absence of any white showing in this eagle’s tail, suggesting an older bird, possibly in its fifth year or beyond. This is an atypical individual with an unusual amount of white (or very light gray) in a sub-adult or adult set of primary feathers, another example of the dangers of relying upon the presence or absence of white in the remiges as a means to age a Golden Eagle.A poorly lit Golden Eagle, or a bird that passes at great distance or high overhead, may provide the observer with little or no opportunity to discern the field marks necessary to answer one or more of the four questions on the “Golden Eagle Field Observation Log with Aging Chart”. That’s O.K., just mark down UNKNOWN for any questions that can’t be resolved with certainty. “Unknown” happens to be a valid answer for using the aging key on the chart.A passing Golden Eagle might never reveal the top side of its wings to an observer. Answer UNKNOWN to question #1 if the presence or absence of tawny wing bars cannot be determined.
Question #2: Is there evidence of molt in the juvenile remiges (primary and secondary flight feathers in the wings)?
Neat and clean. These flight feathers of uniform length show no definitive sign of molt on this young Golden Eagle. Answer NO to question #2 for a bird with a full set of juvenile remiges like these.Note the combination of white bases and dark mottling on primaries one thru three on each wing. Juvenile remiges and rectrices (tail feathers) can be mottled like this on some young birds. Again, answer NO to question #2 for a bird with a full set of juvenile remiges like these. (United States Forest Service image)A full set of juvenile Golden Eagle primary flight feathers, numbers ten through one (left to right). This first set of remiges is longer in length than the sub-adult and adult replacements that will follow. The extensive areas of white may be absent on some birds. (United States Fish and Wildlife Service image)A partial set of juvenile Golden Eagle secondary flight feathers, numbers one through eight (left to right). This first set of remiges is longer in length than the sub-adult and adult replacements that will follow. The extensive areas of white may be absent on some birds. (United States Fish and Wildlife Service image)Answer NO to question #2 when a Golden Eagle is not yet showing any signs of molt in the wings. In addition, note that the bird still has a full set of juvenile remiges. For example, your entry on the observation log under question #2 might read: “NO (juv. set)”.Not all Golden Eagles show white in their first set of flight feathers, but a bird like this with extensive white at the base of the inner primaries can safely be recorded as possessing a set of juvenile remiges. In addition to logging whether or not molt was seen, you can make a note on your entry under question #2 that the bird was showing evidence of juvenile primaries and secondaries. Be aware that in some cases white may remain present at the base of the secondaries through at least a Golden Eagle’s fourth year, but white in the base of the primaries, if present, is lost during the molt process in a bird’s second and third years.An example of the hazards of relying upon the presence or absence of white in the wings to age a Golden Eagle. On this bird, white at the base of the secondaries and not at the base of the primaries indicates only that the bird might not yet be a breeding age Golden Eagle. It tells an observer little about state of a given bird’s molt sequence, that is, whether the remiges are a set of juvenile, sub-adult, or adult feathers. Because the wings show no molt and have a two-toned appearance similar to a Turkey Vulture (see question #3), an observer has an indication that this bird no longer possesses juvenile remiges, so answer NO to question #2 for an eagle like this. In a case when it cannot be determined whether or not feathers from a juvenile set of remiges are present, answer UNKNOWN to question #2. And remember, it’s more important to determine if a passing bird has white in the tail than if it has white in the wings (see question #4).Despite an absence of white patches in the wings, this bird is a classic example of a Golden Eagle with a complete set of juvenile primaries and secondaries. Note the long length of these feathers where the two sets meet, particularly on the left wing. Because these are typically the first of the remiges to be lost and replaced by shorter feathers, a bird molting juvenile primaries and secondaries will show a notch along the trailing edge of the wings in this area. Answer NO to both questions #1 (tawny wing bars) and #2 (molt of juvenile remiges) when observing a bird like this one.A gap is visible on each wing where the inner juvenile primaries are in the process of replacement on this second-year (Basic I) Golden Eagle. Answer YES to question #2 when a gap is visible where these remiges are lost, and new sub-adult feathers have not yet grown in to fill the void. In the observation log, be certain to note details about the status of molt along with your answer. And yes, this bird is passing a hawk watch lookout with a full crop.Note the finely pointed tips on most of the secondary flight feathers on this silhouetted Golden Eagle. These are most frequently juvenile remiges. A gap among them where a feather is missing on each wing indicates molt is underway (appears to be secondary five or six). Answer YES to question #2 when a bird such as this is observed.A Golden Eagle with a noticeable gap in the trailing edge of the wing where a secondary is being replaced. Answer YES to question #2 for a bird with an appearance similar to this.A “Barthelemyi Golden Eagle” (a variant with white scapulars resembling epaulets on the shoulders) showing tell-tale signs of molt, particularly in the left wing where juvenile primary #5 has been lost and is being replaced by a new feather. Age “Barthelemyi Golden Eagles” just as you would those without the white shoulder epaulets.Another look at the “Barthelemyi Golden Eagle” seen in the preceding image. Note the new feather replacing primary #5 in the left wing. Answer YES to question #2 when you can see juvenile primaries and/or secondaries are being replaced.The incremental loss of juvenile remiges and growth of new shorter sub-adult and adult replacements produces an irregular trailing edge of the wing. Answer YES to question #2 when these new darker and more mottled flight feathers are detected. Make a note on the observation log listing the molted feathers. Be as specific as you can, but don’t stress out over it. Just noting that several primaries and secondaries are shorter will help narrow the possibilities when you use the key to age the bird. Look carefully, you’ll see that this eagle is replacing primaries one, two, and three, as well as secondaries one, two, and five on each wing. (United States Fish and Wildlife Service base image by Tom Koerner)A full set of adult Golden Eagle primary flight feathers, numbers ten through one (left to right). Each of the feathers in this set of remiges is shorter in length than the earlier juvenile feathers with which the eagle learned to fly, maneuver, and hunt. (Note: When comparing individual eagles, size can be just as variable as plumage. Females are typically larger than males, but there is also variation within the genders. The adult primaries shown here were sourced from a male bird of larger size than the male eagle from which the juvenile set was derived for the earlier image. Hence, each adult feather in this image is actually longer in length than the one in the same position on the image of the juvenile set.) (United States Fish and Wildlife Service image)A partial set of adult Golden Eagle secondary flight feathers, numbers one through eight (left to right). Each of the feathers in this set of remiges is shorter in length than the earlier juvenile feathers with which the eagle learned to fly, maneuver, and hunt. (Note: When comparing individual eagles, size can be just as variable as plumage. Females are typically larger than males, but there is also variation within the genders. The adult secondaries shown here were sourced from a male bird of larger size than the male eagle from which the juvenile set was derived for the earlier image. Hence, each adult feather in this image is actually longer in length than the one in the same position on the image of the juvenile set.) (United States Fish and Wildlife Service image)The pair of longer secondary flight feathers (probably numbers nine and ten) on this molting bird’s left wing are retained juvenile feathers. Answer YES to question #2 when a Golden Eagle has an untidy appearance like this along the trailing edge of the wings. Make a note on the observation log that these longer juvenile feathers were seen, it may help you age the bird more accurately when using the key. (United States Fish and Wildlife Service image by Tom Koerner)It may be difficult to precisely pinpoint which juvenile secondaries a molting Golden Eagle has retained, but answering YES to question #2 and noting that several were longer will help you assign the bird to an age class without relying upon guesswork.Answer YES to question #2 when a Golden Eagle with a full set of adult remiges like these is seen. Make a note on the observation log that no long juvenile secondaries were seen.Many Golden Eagles will provide no opportunity for the observer to study wing molt. Answer UNKNOWN to question #2 for these birds.
Question #3: Do the undersides of the wings have a two-toned appearance similar to a Turkey Vulture (Cathartes aura)?
Answer YES to question #3 when a Golden Eagle’s primary and secondary flight feathers appear silvery or notably pale in comparison to the darker underwing coverts (left), resembling to some degree the two-toned underwing appearance of a Turkey Vulture (right).Answer YES to question #3 when a Golden Eagle has two-toned undersides on the wings, similar to those of a Turkey Vulture.Answer YES to question #3 if the eagle’s wings resemble those of a Turkey Vulture, just like the ones on the bird in the upper right of this photo (dark inner wing linings contrasting with silvery-gray primary and secondary flight feathers). Answer NO if they resemble those of the younger eagle in the lower left (wings dark below, often with some white bases on the primary and/or secondary flight feathers). Answer UNKNOWN to question #3 if you’re unable to answer YES or NO. (National Park Service image by Kent Miller)
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.
Answer “YES” to question #4 when white is visible in the rectrices (tail feathers). When a bird is observed from an angle similar to this, make a note that a lateral view of a folded tail was seen. Such a view may obscure the dark set of adult inner rectrices that give a 4th-year or 5th-year bird a split-tail appearance.Even at a distance, the white base of this Golden Eagle’s rectrices are apparent. Answer YES to question #4 when white is seen at the base of the tail feathers.Answer NO to question #4 when observing a bird with a full set of tail feathers like those to the left in this image. Answer YES if tail feathers have white bases similar to those to the right. Note the covert feathers at the base of these sets of rectrices. Be careful not to answer YES to question #4 when white is detected only in the coverts and not in the much longer tail feathers themselves. (United States Fish and Wildlife Service image)Answer YES to question #4 if the tail contains any rectrices with white bases similar to these. (United States Fish and Wildlife Service image)A Golden Eagle with a full set of juvenile rectrices (tail feathers).Answer YES to question #4 if the tail contains any rectrices with white bases similar to these. (United States Fish and Wildlife Service image)Answer YES to question #4 if the tail contains any rectrices with white bases similar to the left and center feathers seen here. Golden Eagles are often discovered to be breeding in sub-adult (Basic IV) plumage during their fifth year. Tail feathers with white bases (left and center) are lost during this period. Most birds attain full adult plumage (Basic V) by their sixth year, a full set of adult rectrices lacking white bases (right) having since been acquired. (United States Fish and Wildlife Service image)Top View of a Fourth-year/Basic III (left) and a Fifth-year/Basic IV (right) Golden Eagle- Answer YES to question #4 when white is detected in the base portion of any of the rectrices. Make a note in the observation log if you see a split-tail effect, such as illustrated in the Basic III bird to the left, or if you see only very limited white in the tail, such as depicted in the Basic IV bird to the right.Make a note on the observation log if darker rectrices like these are creating a “split-tail” look or other appearance as they grow in among lighter juvenile or sub-adult feathers. (United States Fish and Wildlife Service image)Keep in mind that mottling can be present at any age and, even among adult Golden Eagles, it can be quite variable. (United States Fish and Wildlife Service image)White cannot be seen in the rectrices of this Golden Eagle. Answer NO to question #4, but you should note on the observation log that it was a lateral view of the bird. A top view of a spread tail must be seen to confirm the absence of any white-based feathers. Notice the tawny wing bars on this bird. Nice. (United States Fish and Wildlife Service image by Tom Koerner)Beware: Fluffy white covert feathers surrounding the base of the rectrices can create the illusion of white in the tail feathers, particularly on older Golden Eagles. If you’re not certain whether the white you see is in the base section of the tail feathers or is instead in the covert feathers surrounding the tail, answer UNKNOWN to question #4. Log the same answer if conditions such as backlighting, distance, or a lateral view of a folded tail prevent adequate study of the eagle’s rectrices.A Golden Eagle showing very pale undertail coverts, but no white in the rectrices, may very well be an adult bird. However, unless you can see the dorsal side of the spread tail to confirm the absence of white in its flight feathers, you’ll have to answer UNKNOWN to question #4.Caution: Sun reflecting off the glossy surfaces of a set of adult rectrices can give the illusion of white in the tail. Though there is pretty strong evidence that this eagle has no actual white in the tail and is probably an adult in definitive plumage, we need to see the top of the spread tail to be sure, so mark down UNKNOWN for question #4 (white in the tail), but YES for question #3 (two-toned undersides on the wings).The preceding bird as it passed the lookout. Careful examination revealed the underside of the tail was not white, despite appearing that way in direct sunlight.
STEP TWO
Enter the date, time, and flight information for your sighting in the appropriate boxes below the blue headings on the observation log.
STEP THREE
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
After you’ve recorded the age class code for each bird on your observation log(s), this Golden Eagle Aging Codes and Nomenclature chart can be used to help analyze your sample. Click the image to enlarge.
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.
SOURCES
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.
Wheeler, Brian K. 2018. Birds of Prey of the East: A Field Guide. Princeton University Press. Princeton, NJ.
