|DN4 at the Decorah North Nest|
Enjoy the downy bobbleheads this week! By next week, they will already be growing their longer 'wooly' second or thermal down and alternately worrying and thrilling us with their interactions and sojourns around N2B.
The general stages of eagle development are:
- Stage 1 - Structural growth. In their first thirty-five to forty days of life, eagles grow very rapidly, gaining weight and building bones, muscles, tissue, and features like tarsi, footpads, toes, and claws. This phase of development slows down about halfway through an eaglet's time in the nest, even though individual features might continue some level of growth.
- Stage 2 - Feather and flight-related growth. Eagles grow four sets of feathers - natal down inside the egg, thermal down, juvenile feathers, and adult feathers. While thermal down starts growing at about ten days and juvenile flight feathers at about 27 days, feather growth doesn't overtake structural growth until thirty-five to forty days after hatch. Flight muscles also begin growing as eaglets wingercize, flap, hover, and eventually branch and fledge.
- Stage 3 - Neurological Coordination. Eagle watchers know how ungainly eaglets can seem! As they grow, they become more adept at controlling beaks, legs, wings, and feet. They learn to stand on their own feet, tear food, self-feed, and flap their wings, going from cute but clumsy clown clompers to graceful young eaglets poised at the edge of fledge.
I'm not sure how familiar many of you are with the cortical homunculus, an image-based tool that maps tactility. We discussed it very briefly in this blog and I'll include links below. While useful and extremely cool, most cortical homunculii are static - that is, they reflect just one phase (usually adult) of an organism's life. But an eaglet's cortical homunculus will differ from an adult's as body parts and associated skills are gained and neural pathways developed. Our eaglets' brains and bodies are rapidly growing and changing as they gain the skills they need for life outside the egg!
Things that helped me write this blog, with a few considerations:
- Eaglet hatch weight is based on Gary Bortolotti's work with eaglets at Besnard Lake in Canada. It is possible that our eaglets are a little smaller than his, since Bald eagles get bigger the farther north one travels: a phenomena known as Bergmann's Rule. Bortolotti's paper makes for interesting reading and provides a great look at the work involved in field science. Citation: Physical Development of Nestling Bald Eagles with Emphasis on the Timing of Growth Events, The Wilson Bulletin, Vol. 96, No. 4 (Dec., 1984), pp. 524-54. https://www.usask.ca/biology/bortolotti/pubs/wb96-4-524-542.pdf. Thanks to The Wilson Ornithological Society for their permission to use this chart.
- Mouseunculus: http://phenomena.nationalgeographic.com/2013/07/24/mouseunculus-how-the-brain-draws-a-little-you/
- Homunculus: http://io9.com/5670064/how-your-brain-sees-your-body-meet-the-cortical-homunculus
- Input from Bob Anderson, who imparted much wisdom and information before he passed.
- RRP moderators and their calendars, lists, books, charts, and personal observations.