We’re writing a series of blogs about the first few weeks of an eaglet’s life. An eaglet spends roughly 75 to 80 days in the nest. For about the first half, it grows and gains weight. For about the second half, it grows flight feathers and starts developing the skills it will need post-fledge. We will focus on week three in this blog.
TE3 turned 20 days old today. During week two (seven to 14 days), its footpads and talons grew, its feet and legs yellowed, its talons started turning black, and its grey thermal down started sprouting! For the first few days of TE3’s life, Mrs. T carefully placed tiny morsels of meat into its gaping, sometimes unsteady beak. As week two progressed, she dangled larger strips of flesh for TE3 to lunge at, which improved the eaglet’s visual acuity and feeding skills. It had a fine fishy buffet to chose from, including sucker, carp, and drum from the Mississippi (look for rougher scales and a bottom pointing mouth with fleshy lips), blue jay, coot, opossum, squirrel, and rabbit. Of course, all that food resulted in a whole lot of eaglet poop. As it got stronger and more coordinated, tree-rrific TE3 got better at sitting up, bending over, and shooting poop!
Fish, fish, and even more fish!
Bald Eagles are piscivorous by preference, but TE3’s diet is fish-heavy even when compared to our other nests. We’ve talked about the ways in which neighborhood influences nest and this is a prime example! The T’s are nesting in a yard along an islanded stretch of the Mississippi River. Islands create zones of reduced flow where sediments, detritus, and larvae can accumulate; provide cover and foraging areas for juvenile fish; and support aquatic vegetation, which contributes to oxygenation, shelter, and spawning grounds. In short: structure supports fish populations, and where fish are abundant, eagles thrive.
Mrs. T is the lone provider and pressed for time and resources. Her mammalian neighbors aren’t spending much time on mowed grass and are generally harder to catch, although we’ll most likely see an increase in mammalian prey once unwary kits, kittens (baby rabbits), and pups begin leaving dens and holes. In the meantime, Mrs. T is focusing on a reliable, relatively easy source of food to provide for TE3 and herself. All meals are welcome, but there are a lot of fish on the Trempealeau Buffet!
Is TE3 lonely?
Watchers often wonder about the life of a single eaglet. Is TE3 lonely with no siblings to play with and bonk? Remember, this is all the eaglet has ever known, so it has no basis for comparison. And its world offers plenty of stimulation, including time with Mrs. T, an occasional visit from Mr. T, a squirrel with the zoomies, and visits from neighboring nuthatches! All of these things give TE3 an opportunity to learn and practice the fundamentals of eagle life: play, observation, competition, allopreening, vocalizing, and defense. Nest neighbors like this keep life exciting!
Filial imprinting is an enjoyable part of nest watching and an important part of early eagle learning. But it’s not the only way that eaglets learn about or experience the world around them. Our sensational singleton is learning and growing every day.
Milestones from TE3’s third week include…
- Mohawks! Natal down disappears from the head last, giving TE3 a distinctly punk rawk vibe as its grey thermal down came in.
- Thermal down: As much as I love the fluffy white bobblehead stage, it was a relief to see TE3’s grey flannel pajamas replace its natal down. TE3 isn’t completely waterproof, but it’s less vulnerable to cool, wet weather than it was just a week ago.
- Cropzillas! Eagles store food in their crops until their stomachs are ready for more. This mini ‘pantry’ helps ensure that rapidly growing eaglets get the nutrients and calories they need, when they need them. We saw crops in the first and second weeks, but holy cow – how did TE3 not crop flop over this week? And remember those bigger chunks of scaly fish? TE3 cast its first pellet this morning! https://youtu.be/wdArBN5lNPQ
- Eaglet exploring: TE3 shuffled around its nest, defended itself against a squirrel with the zoomies, and expanded its boundaries as it learned more about the world around it. It’s a big world, and our eaglet explorer is just getting started!
- Pinfeathers and clown clompers! We saw the very beginnings of pinfeathers at the end of TE3’s second week, but they are clearly emerging now. Its footpads are growing rapidly and starting to assume clown-clomper proportions. Next step? Standing!
Happy three-week birthday TE3, and welcome to week four! Your human aunties and uncles are rooting for you!
As of this blog, our sensational singleton is about 25% of the way through life in the nest. Our adorable little bobblehead has been (mostly) replaced by a large grey tween eagle. Enjoy white down and earholes while you can!
Fourth week preview
Watch those clown clompers really take off in TE3’s fourth week! Think they are oversized now? You ain’t seen nothing yet!
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. Thermal down starts growing at about ten days, juvenile deck feathers at about 20-23 days and juvenile flight feathers at about 27 days, but 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.
- Neurological coordination occurs throughout an eaglet’s time in the nest. During week two, their eyesight and basic coordination skills are improving as they grab food from Mom and Dad, sit up tall for feedings, shuffle around on their tarsi, and explore the world with their sensitive beaks. As they grow, they will become more adept at controlling beaks, legs, wings, and feet. They will 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. 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! Areas related to visual acuity, strength, and coordination all ‘lit up’ in week two as the eaglets got better at perceiving things at a distance, improved their poop shooting, reached for food, took bigger bites, and started exploring!
Things that helped me write this blog, with a few considerations
- Eaglet weight and growth 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
- 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.
The Raptor Resource Project