Looking for the clues that distinguish one nestling from another is like trying to looking at the difference between little brown bird A and little brown bird B. Subtle differences make all the, well, difference. Other clues (the type of down and emergence and length of pin feathers, for example) can provide clues about the bird's age. Training yourself to see these differences will not only help you identify D12, D13, and D14, but will also help greatly with bird identification in the field - even if the field is your bird feeder or computer screen.
- Size. As time goes on it may be more difficult to note size differences. Initially, those differences will be based on age. Once the eaglets achieve full or close to full growth, size differences will be largely gender-based. Even within the context of gender, however, there will probably always be at least subtle size differences. In Bald eagles as in other raptors, females are larger and males are smaller.
- Coloring. Actual colors will be similar, but shades of the color may be quite different. Look for patterns of light and dark, and any identifying marks.
- Type of Down. Does the nestling have natal down (white and fluffy), or the thicker wooly secondary down also called thermal down? More information on plumage stages can be found here: http://www.swbemc.org/plummage.html.
- Pin Feathers. Are pin feathers starting to come in? Note the location of emerging pin feathers. We've used pin feather length to help identify the age of young peregrine falcons when banding them.
- Hairdo. This is one way we learned to differentiate nestlings last year. Does the eaglet have a crew cut, a mo-hawk, or an Elvis-style hairdo? Are the eaglet's "bangs" straight across, or do they come to a single point, or is there a double point like an "M" or a "W"?
- Facial Features - Around the Eyes. Look at the area around the eyes - do you notice a streak or a dot, or a dark mask as contrasted with a lighter mask?
- Facial Features - Beak Size and Coloring. Does one eaglet have a larger beak as compared to the others? Look at the coloring on the beak. Is the beak tip dark, or perhaps the darker coloring extends to mid beak.
- Leg Coloration and Foot Size. What color are the eaglet's legs? How big are its feet? Is there anything noticeable about the talons? We've seen blue-legged and white-taloned peregrine young. Color differences can provide a valuable clue.
- Behavior: Is this a noisy or a quiet eaglet? Is this a busy eaglet or a lazy eaglet? Does this eaglet prefer to rest alone or with a sibling? What nest area does the eagle frequent the most? All of these behaviors can provide identification clues.
Here are some observations that might help identify D12, D13, and D14. See if you can spot them, or share your own in the comment section. Of course these are my observations on April 10, 2012. Yours may be different. At the rate they are growing, mine will!
- Has a 'sad-looking' beak that stops midway of eye.
- Has a ^ above the blackening of the eyes.
- Has a skinnier neck than D13 and is whiter for now.
- Has a more messy look of blacking around eye.
- Has a 'drip' under left eye.
- D13's beak goes back to back of eye, and has a jiggy-jag to it.
- Is getting larger than D12.
- Is the smallest so far.
- Doesn't miss a meal.
- Has a strong neck
- Knows how to bonk D12 and D13