Golden Eagles are large birds with extremely
long, broad wings, which are held in a dihedral when soaring and
slightly bowed when gliding. They appear slow moving in flight,
and exhibit heavy, languid wing beats. Golden Eagles are dark with
a golden nape (typically appearing all-dark at a distance) but
immature (all ages except adult) birds have varying amounts of
white in the wings and tail. Adult Golden Eagles are present along
the Wasatch Mountains most times of the year, but during spring
and fall migration Golden Eagles of all ages are seen with
regularity.
In flight, many Golden Eagles are difficult or impossible to age
without seeing the bird’s topside or the tail fully spread.
However, it may be possible to see white in the wings or tail, or
molt in the flight feathers (tail and wings) to narrow the age to
non-juvenile or non-adult. This article is made to point out the
difficulties in ageing 1-3 years old Golden Eagles in flight,
since birds 1-3 years old with white in the wings or tail look
similar in plumage to each other.
Underside
Juvenile (up to one year old), sub-adult I (1-2 years old), and
sub-adult II (2-3 years old) Golden Eagles are often inseparable
in the field without ideal, close-up views. All three ages have a
white tail with a dark tip, and varying amounts of white along the
base of the primaries gradually becoming uniformly dark as they
reach full adult plumage, which takes from 4-6 years. The white in
the tail is typically extensive, covering more than half the
length of tail, but can be restricted to the base in rare cases (Figure
4, left / juvenile). Sub-adult I Golden Eagles (Figure
2) retain most of their juvenile feathers and appear nearly
identical to juveniles (Figure 1) in the
field. Also, the inner primaries, inner secondaries, and central
tail feathers that are replaced on sub-adult I birds are
impossible to distinguish.
Sub-adult II Golden Eagles (Figure 3) are
comprised of mostly sub-adult feathers, with some retained
juvenile feathers. On some sub-adult II birds, the central tail
feathers may be replaced with adult feathers, causing the tail to
look dark centered or ‘split’ (but this usually occurs on
sub-adult III birds). Sub-adult II birds may replace all of their
juvenile secondaries, but sometimes retain a few juvenile
secondaries, which will project slightly beyond the rest of the
wing. On sub-adult II birds, primary molt occurs towards the outer
end of the wings, thus, a Golden Eagle with a white base to the
tail that is molting outer primaries is almost certainly a
sub-adult II bird. Birds that are not actively molting are
difficult to age.
Upperside
The upperwings of juveniles are uniformly brown, but the upperwing
coverts and golden nape typically fade by spring and appear paler
than usual (Figure 4, middle). Juveniles
lack any signs of molt (replacement of feathers) during fall, with
their wings looking even along the trailing edge; other ages often
show wear along the edge of the wings. Juveniles are also the only
age to lack pale, mottled upperwing ‘bar’. Golden Eagles with
extensive white wing patches to the underside of the wings often
show small white patches on the upperside of the primaries (Figure
1, right).
Some upperwing coverts on sub-adult I Golden Eagles are replaced,
with the new pale feathers forming a narrow, mottled upperwing
‘bar’. The faded upperwings of juveniles in spring are broad and
even-toned.
Be careful, certain traits on Golden Eagles can be misleading. In
direct sunlight, the pale undertail coverts can be mistaken for
the white tail base of immature birds. In spring when the head is
faded, Golden Eagles may exhibit a pale-headed appearance that can
look like the white head of a Bald Eagle (Figure 4, middle /
juvenile). Also, the flight feathers (including the grayish tail
bands) of adult Golden Eagles may appear whitish similar to
immature birds when illuminated by snow cover (Figure
4, right).
Photos by Jerry Liguori
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