by Sherri Elliott
Bald Eagles have over 7,200 feathers (yes, researchers study and have counted them) and each plays a remarkable part in physiology, flight, and insulation. While Bald Eagles will go through multiple plumage changes before maturity at age five when heads and tails become fully white, head feathers and upper tail coverts can be distinctly colored and patterned as they segue or transition to body or tail.
January 2, 2020: Decorah Mom head feathers and nape
Thanks to the camera operators we have closeups of Mom Decorah’s back head feathers showing the stiffer black rachis (shaft) with interlocking barbs and vane, in addition to the streaks of pure white and chocolate that mix as they transition to nape and mantle feathers. The frost of the morning is still on her upper shoulders, showing how well insulated her feathers are in cold weather.
January 2, 2020: Decorah North Female preens upper tail coverts
The patterns are also interesting on the upper tail coverts below the rump and above the tail, as seen by the Decorah North Female (DNF) as she preens each feather carefully and with precision, zipping her feather barbs and distributing the uropygial gland oil which helps keep them healthy and water repellent.
Both Decorah Eagles Nest and Decorah North Nest are live-streamed 24/7 by Raptor Resource Project.
To learn more about bird anatomy, we love the Cornell Lab of Orinthology. Here’s a great link: https://academy.allaboutbirds.org/features/birdanatomy/