Feathers are fabulous! Not only is each feather on a bird’s body different from every other in length, shape, structure and function, but feathers also differ between species and between sexes and ages within a species.
For example, young raptors often have noticeably longer flight feathers in the wings and tail which provide additional stabilization, making it easier to fly. This is similar to training wheels on a bicycle.
The feathers at the top of the wrist are called “alulas”. They originate from the first digits of each wing, similar to our thumbs. The position of the alulas during flight can be altered to create drag for different flight maneuvers. Raptors typically have between 3 to 5 alula feathers on each wing.
We wanted to use feathers from Freedom, the bald eagle whose training you have been following, to demonstrate this. We keep all of the feathers that he has molted - which means he has already replaced some from when he was a hatch year bird last year. (Molted feathers are easy to place next to a ruler to show you measurement.) We are comparing them to a current bald eagle patient, since we could put a measuring tool next to them while the patient was on the table. What we will show you is that the alula feathers from a hatch year bird (Freedom's molted feathers) are a different length than those same feathers on a bird who is older.
|This is the wrist and alula feathers of a second year bald eagle patient.|
|This is a ruler showing you the length.|
|These are Freedom's molted alula feathers from when|
he was a hatch year bird. Can you see that they are about
three inches longer?
The first photo is of the male bald eagle patient. The top of the wrist is at the top of the photo. You can see the three alula feathers. These feathers are not his hatch year feathers. They have already molted. (You can see how fresh and dark the newer, molted alula feathers are.)
The second photo is of that patient bird, with a ruler next to the feathers, so you can see the measurement.
The last photo is of Freedom's molted alula feathers from when he was a hatch year bird. They are almost three inches longer!