Rare Barthelemyi Variant of the Golden Eagle Seen Migrating Along Second Mountain

As the autumn raptor migration draws to a close in the Lower Susquehanna Valley Watershed, observers at the Second Mountain Hawk Watch in Lebanon County, Pennsylvania, were today treated to a flight of both Bald and Golden Eagles.  Gliding on updrafts created by a brisk northwest breeze striking the slope of the ridge, seven of the former and three of the latter species were seen threading their way through numerous bands of snow as they made their way southwest toward favorable wintering grounds.

The best and final bird of the day, and possibly one of the highlights of the season at this counting station, was a “Barthelemyi Golden Eagle”, a rare Golden Eagle variant with conspicuous shoulder epaulets created by white scapular feathers.

"Barthelemyi Golden Eagle" passing the Second Mountain Hawk Watch in Lebanon County, Pennsylvania.
The grand finale, a “Barthelemyi Golden Eagle”, passed the Second Mountain Hawk Watch during a break in the afternoon’s snow showers.  Note the bright white scapulars at the base of the leading edge of the wing.
"Barthelemyi Golden Eagle" passing the Second Mountain Hawk Watch in Lebanon County, Pennsylvania.
Barthelemyi variants are known from populations of Golden Eagles in the Alps of southern Europe and from both eastern and western populations of birds in North America.  Spofford (1961) documented a pair of Golden Eagles with the Barthelemyi traits nesting in eastern North America.  In two successive seasons they produced young that developed the same plumage characteristics, suggesting the variation may be passed to offspring by one or more genetic alleles.

Today’s rarity is the second record of a “Barthelemyi Golden Eagle” at Second Mountain Hawk Watch—the first occurring on October 21, 2017.

SOURCES

Spofford, W. R.  1961.  “White Epaulettes in Some Appalachian Golden Eagles”.  Prothonotary.  27: 99.