Eaglet Growth and Development: Week Three

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.

D32 and D33 are 16 and 13 days old. During week two (seven to fourteen days), the eaglets’ footpads and talons grew, their feet and legs yellowed, their talons started turning black, and their grey natal down started sprouting! During week one – especially the first few days – Mom carefully placed tiny morsels of week into gaping, sometimes unsteady beaks. During week two, she dangled larger strips of flesh for hungry eaglets to lunge at, improving visual acuity and feeding skills. When it wasn’t too cold or wet to require brooding, the eaglets were eating, bonking, or recovering from a meal. They had a fine buffet to chose from, including trout from the hatchery (look for finer scales and a front pointing mouth with thin lips), sucker (look for rougher scales and a bottom pointing mouth with fleshy lips), and what might have been a pheasant. Of course, all that food resulted in a whole lot of eaglet poop. Little slices went to big spatters on the crib rails and poopcasso tree as as the eaglets got better at sitting up, bending over, and shooting poop out of the nest…or at a parent who accidentally ended up in the line of fire!

When will D33 catch up with D32? It’s going to be a while. Both eagles are rapidly gaining weight, but sex doesn’t take over from age as a size determinant until about 50 days of age. Concerned about feeding? Trust the crop! If D33 has a crop, it’s getting fed – whether we see it or not.

We saw whole lot of eating and sleeping during week two.  While big changes are on the way, week three (14 to 21 days) will involve a whole lot of, well, eating and sleeping as the eaglets enter the steepest part of their weight curve! Here are some things to watch for:

  • Mohawks! Natal down disappears from the head last, which will give the eaglets a distinctly punk rawk ‘do in the next seven days or so.
  • Cropzillas so heavy that the eaglets have a hard time sitting up! Given that bites now include scales and fur, we will likely see pellet casting this week.
  • Pinfeathers! Look for pinfeathers to start emerging along the edges of wings.
  • Eaglet explorers! While the eaglets can’t stand on their feet yet, they will begin to expand their explorations as they grow older and (hopefully) the weather becomes a little warmer and drier.
  • Clown clompers! Feet pads and legs/tarsi will grow like crazy, as this chart from Gary Bortolotti shows! You think those footpads are big now? Just wait!Eaglet Footpads

By the end of week three, the eaglets will be about 25% of the way through life in the nest. Our adorable little fuzzballs will have been (mostly) replaced by large grey tween eagles. Enjoy white down and earholes while you can!

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: