Saturday, December 10, 2011

All Those Not-so-bald Eagles

Subadult Bald Eagle (c) John Ashley
A courageous Magpie joins a two-and-one-half year old Bald Eagle for lunch on a deer carcass.

This evening I watched no fewer than nine Bald Eagles take turns feeding on a deer carcass in a foggy field of stubble. One or two at a time would fill their crops with red meat - in some unspoken eagle pecking order - while the rest watched from favorite trees along the river.

Subadult Bald Eagle feeding on a deer carcass (c) John Ashley
Banding juvenile Bald Eagle.
(Click to see the dark beak.)
A lot of people I know think Bald Eagles have white heads and tails and Golden Eagles are just that, golden-brown. That makes life real simple. The only problem is that it leaves out the majority of Bald Eagles, the many sub-adults that aren't old enough to have solid white head feathers.

Bald eagle plumage basically goes from dark to light with age. They start off chocolate-brown with various amounts of white feathers here and there during their first three years - but not just in those areas that will be white in adult plumage. With all the variability in feather colors, it's easier to focus on eye and beak colors.

Banding a juvenile Bald Eagle(c) John Ashley
Juvenile Bald Eagle with dark eye and beak.
(Click to raptorize.)
Juveniles just off the nest (first-year birds) have dark eyes (irides) and black beaks from the nose holes (nares) forward. A second-year bird will still have a dark beak, but its eyes will lighten to a buffy brown. A third-year bird will start showing some yellow on the forward half of its beak, and its eyes will lighten even more to a creamy tan.

A forth-year bird is finally starting to look the way we think a Bald Eagle should. A few dark feathers remain on an otherwise white head and tail, the beak is mostly yellow, and the eyes are dull yellow. And if the Bald eagle lives to be five years old, it will finally look very distinguished with its bright white head and tail, solid brown body, and bright yellow eyes and beak.

If the eagle in question is anywhere near water, you're almost certainly looking at a Bald Eagle. They are mostly denizens of large lakes and rivers. Golden Eagles are denizens of high desert plateaus and mountains. as they prefer higher and dryer terrain. About the only notable overlap in is the high desert winter, where some Bald Eagles spend the icy months dining on jackrabbits.

You can find a detailed description of Bald Eagle ages here, and you can find the answer to just about any question you might have about them here.  Information on aging Golden Eagles is found here.

One and one-half year old Bald Eagle (c) John Ashley
One and one-half year old Bald Eagle with dark beak and buffy brown eye.