Gorgeous, no? An adult redtail who visited yesterday. One of only two birds who stopped by when I was banding, but definitely worth all the hours in the blind.
A profile showing some of her beautiful details. We aged her as "After Second Year", which means we know she was hatched in 2011 or earlier. I'm guessing, based on her plumage, that she can be more specifically aged as a third year bird, i.e., hatched in 2011. (More about that as I go through the pix.) As redtails age, their eyes darken from yellow to dark brown. She has milk-chocolate eyes, so not quite as dark as they'll get. Note the little ring in her iris... I thought was an elegant touch.
She blinked her eye just as I was taking this so I got a photo of her nictitating membrane - a translucent third eyelid that can protect their eyes but still allows them to see fairly well. It looks like there's something inflamed in a small part of a blood vessel at the corner of her eye.
One of the things I love about banding is that we get to see some of the fine details of plumage that you would never see in the field, like the beautiful feathering on the nape of her neck. You can also see the curve of her gigantic all-seeing eye.
So how do we figure out her age? We know juveniles and adults have very different plumage. For one thing, kids don't have the stunning red tails, like the one above. One thing that can be confusing is that the outer tail feathers on redtails often look very different from the others. On juveniles, you may see outer tail feathers with a bit of red in them, and adults may show greys and browns along with the red, making them look more like juvenile feathers. Redtail plumage is crazy with variation.
When they've got juvenile plumage this time of year, we know they were hatched this year. When they have a mixture of juvenile and adult plumage, we know they were hatched last year. When they have a mixture of old and new adult plumage, we know they were hatched at least two years ago, but it can be difficult to say specifically how many years ago.
On a redtail, the best place to look for retained feathers is in the wings. Because redtails' flight feathers are large, they take a couple of weeks to grow (less for the smaller secondaries, more for the longest primaries). They can't afford to be missing too many at once, lest it compromise their flight abilities, and the energy demands of molting mean they can't typically do it during the winter or when they're breeding. That leaves a window of just a few months to replace those feathers, and it means that they almost never replace all of them in a single year. Looking for last year's flight feathers helps us age them.
The easiest way to see the wear and fading that helps tell old from new feathers is from the dorsal (upper) side of the wing. In the first of these three wing photos, you can see the contrast between fresh, dark feathers and older, faded and worn feathers. To tell juvenile from adult feathers, it's better to look at the ventral (under) side of the wings, like the other two wing photos. Juvenile feathers have a narrower subterminal band (the wider dark band along the trailing edge of the wing). Adults have a heavier subterminal band, and it often has a "spraypainted" appearance like this one. The secondaries on juveniles are noticeably shorter than adult secondaries, giving the wing a distinctive uneven edge. (I think I have some photos that show this - will look and post.) This is something that can be seen pretty easily on soaring birds, so it's the one thing that would let you age a second year bird in the field.
One other thing is the feathers are generally replaced symmetrically - both #1 primaries normally drop within a day or two of each other. You can see that symmetry if you look closely at these two wings. If you see one feather that's outside the pattern, it could be that it was lost in an accident and then replaced.
Wow, that proved harder than expected. I took dozens of documenting photos back in the film days, but apparently not so much in recent years. Anyway, this bird shows one retained juvenile feather in the secondaries - notice the one that's faded and about half an inch shorter than the rest. Typically, they have a few more than this - usually 2-4 retained secondaries. Even though it shows the top side of the wing, you can still see the subterminal band pretty clearly, so you can see how narrow it is on the juv feather compared to the adult feathers.
And a beautiful end to the day... fog thinking about creeping in as I walked down from the hill.