Friday, April 13, 2018

Eaglet Growth and Development, Week Two

It is April 13 as I write this, and our eaglets are growing rapidly! In Decorah, D29 is twelve days old, D30 is eleven days old, and D31 is nine days old.

Left to right: D30, D29, D31
In their second week of development, the eaglets will gain roughly two pounds between their 7th and 14th day of life. They will experience rapid growth in features like beaks, culmens, and footpads, start replacing their white natal down with thicker grey thermal down, and begin exploring the nest. Although they aren't yet standing on their toes, they are able to sit up - way up! - for feeding and shuffle around on their metatarsi. Their eyes are wide open and fit more comfortably in their eyesockets, features like brow ridges are beginning to appear, and their legs and footpads are yellow, not pink. Gary Bortolotti wrote that bald eagles might gain more weight per day than any other north American bird, although the majority of their weight gain occurs within the first 30-40 days. This rapid weight growth is fueled by their nutrient-rich diet of meat. Over the past week or so, we watched the eaglets chow down on fish, rabbit, squirrel, ground squirrel, coot, groundhog, and unidentified birds. D29 became proficient enough at shooting poop to christen the Poopcasso tree on April 9th, although it was quickly joined by its siblings on April 11th and 12th. While babylet battling hasn't entirely subsided, it has become less intense as pecking orders are established and eaglet crops are repeatedly stuffed until they look ready to burst! The eaglets are alternately hitting, submitting, and quitting to cuddle in the nest cup, grow, and wait for more food to arrive. We haven't gotten to see much of them given the cold, but D29 did finally escape the nest cup during warmer weather Wednesday!

So what did we see in the nest this week?


 April 8: Eaglet explorers. Despite the cold weather, the eaglets are busy popping out from under Mom and Dad and starting to nibble at nest materials, exploring  the world with their sensitive beaks and tongues.
April 9: Preening! When birds preen, they remove dust, dirt and parasites from their feathers and align each feather in its optimum position. D29's exploratory downy nibbles today marked an important first step on the road to feather care!
April 10: Thermal down begins to emerge! A hatchling eaglet's fuzzy white natal down doesn't assist thermoregulation, aka controlling one's temperature. Denser thermal down provides more insulation and helps nestling eaglets keep their body temperatures at a relatively constant 105'ish degrees. 

April 11: Eaglet escapee! D29 took its first sojourn out of the egg cup today! At ten days of age, D29 weighs between about 2 and 2.5 pounds. It can't stand on its feet, but it can sit upfor feeding and shuffle around on its metatarsi. Its feet and toes are yellow, but its tiny talons are still clear.

April 12: Cropzillas! D29 has just gorged itself on more food than it can stomach! It will store the food in its crop until it is ready to transfer it to its stomach for digestion. This mini 'pantry' helps assure that the rapidly growing eaglets get the nutrients and calories they need, when they need them.

Painting the Poopcasso tree! On the morning of April 9th, the eaglets weren't quite shooting poop as far as the Poopcasso tree. D29 christened it that day, and all of the eaglets were hitting it by the 13th!
In the week to come, we can expect (continued) rapid growth in footpads, talons, and legs. Beak growth will rapidly slow as the eaglets' beaks approach adult size and we may see dark juvenile feathers start to sprout from their grey down. Overall weight and height gain will continue, most likely reaching their steepest curves some time this week. By the end of their second week of life, our little bobbleheads at Decorah will be almost a foot tall! Enjoy eaglet earholes and egg teeth while you still can - their earholes will soon be covered by down and their egg teeth are wearing away.

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! I'd tend to think that visual acuity and eaglet beak and tongue sensitivity  suddenly 'lit up' this week, leading changes in coordination as the eaglets began sitting up, grabbing food, moving around, and preening and nibbling at things.

Things that helped me write this blog, with a few considerations:
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