Eaglet Growth and Development: Week Four

D24 and D25, April 25, 2016

D24 is 28 days old today, while D25 turns 26 days old. At this point, feather growth is starting to overtake structural growth as the eaglets approach the half-way point in the nest. Pinfeathers emerged this week, growing at an astonishing rate as they poked out from their keratin sheaths along the edge of the eaglets' wings. Feathers also started to emerge along their backs - the 'cloak' - and sprout from their tails. As beak, leg, and footpad growth began to slow, wing growth sped up, leaving the eaglets with noticeably longer, larger wings by the end of week four.

We also saw changes in behavior. Although the eaglets will continue to compete for food, baby bonking has ceased. This always makes me wonder what functions it serves. We know it strengthens muscles, aids coordination, and helps improve eyesight. Does food competition lead to greater food intake, helping to fuel an eaglet's rapid growth? Does it lay the ground for future social interaction, which includes plenty of body language, vocalization, and dominant/submissive interaction? Does it give parents information about an eaglet's overall heath, or help prompt provisioning? Or is it simply replaced by a new suite of physical behaviors as the eaglets begin to explore the nest and enter the next phase of nestling life? Bonking may have ended, but the eaglets are starting to play with sticks, move towards a full stand, and expand their explorations of the nest. They've also begun noticing the area around the nest, tracking with Mom and Dad as the adults pay attention to the outside world.

So what can we expect to see in week five? Watch for an explosion of dark feathers, leading to an evenly mottled grey and white appearance some time in the next week. The eaglets will begin standing and walking, leading to many mouse clicks as we try to shoo them back to the center of the nest! We may see them begin to tear their own food and we will get to see them 'play house' as they begin moving sticks around themselves and with Mom and Dad. If past years are any judge, Mom and Dad will give them plenty of materials to work with as they pile up the crib rails with larger, heavier sticks!

We've talked a lot about physical changes. We are also entering a period of rapid developmental changes as the eaglets acquire new skills and grow feathers. The eaglets will play cooperatively and competitively, learn to stand, walk, and tear food, and begin moving their wings. Following the appearance of Mom's teakettle whistle, I'm waiting for baby vocalizations to turn into juvenile screes for food! I'm looking forward to watching D24 and D25 move into the next phase of their lives as feather growth takes over from body growth and greater mobility leads to changes in behavior.

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.

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.

So where is our cortical homunculus in weeks 4-5? I'd tend to think that legs, feet, and wings are accelerating in importance this week, leading important behaviors like standing, tearing, and flapping! I also wonder what impressions are being made now that they are beginning to pay attention to the outside world and have moved from playing with grass to nibbling at larger, heavier sticks. The nest and eagles always have more to teach us!

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.

Eaglet Growth and Development: Week Three

04/13/16: Decorah Nest	04/13/16: Decorah Nest
04/19/16: Decorah Nest	04/19/16: Decorah Nest

D24 is 22 days old today, while D25 turns 21 days old. In the past week, the eaglets' footpads and talons have grown, their feet and legs have yellowed, and their talons have turned almost entirely black. Their mohawks have become more apparent as they shed their white natal down, which disappears from the head last. Almost every time I checked in, the eaglets were either eating or recovering from a meal. Their crops bulged so heavily at times that it was hard to believe they could sit up! They also 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), rabbit, muskrat, and even a mink.

Eaglets spend roughly 75-80 days in the nest, so we are a little under a third of the way to fledge. Most birds of prey seem to spend roughly the first half of nest life gaining weight and growing structural features like footpads, talons, toes, and beaks. While some structural growth may occur later on, the second half of nest life is dedicated to feathers and wings as feathers replace down and wings lengthen.

This week we were treated to a lot of eating and sleeping, but big changes are on the way! Pinfeathers started growing out late in week three and poop went from little slices to big spatters as the eaglets got better at sitting up, bending over, and shooting poop! What else can we look forward to in the coming week?

• The eaglets should start standing on their feet. This will change nest exploration and enable them to really get to work on the Poopcasso tree!
• Natal down mohawks will vanish and dark deck feathers will poke through the eaglets' natal down at an astonishing rate.
• Still enclosed in their keratin sheaths, eaglet pinfeathers will grow longer. 
• We may be treated to the beginning of wingercizing sessions! Once the eaglets can stand, they can really begin exploring their wings. 

By the end of the fourth week, the eaglets should be standing well and may be starting to walk and tear their own food. I have no doubt that many of us will be mouse-clicking, shoeing, and blowing to get inquisitive eaglets back into the center of the nest as they widen their explorations and begin broadening their horizons! 

While we've been making guesses at gender, the weight of the two sexes begins to separate as females gain weight faster than males.  Sex takes over from age as a size determinant around 50-60 days. But cameras can be tricky and clutches can have large males and small females or be all one sex, making ID impossible without measurements or a genetic test. We'll have a lot of fun seeing if size conforms to our observations based on what we have seen of beak size, commissure extension, and other traits, and I can hardly wait for food tearing and wingercizing!

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.

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! I'd tend to think that legs, feet, and wings are starting to 'light up' this week, leading important behaviors like standing, tearing, and flapping!

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.

Thank you to our volunteers!

This week is National Volunteer Appreciation Week! I wanted to take the time to thank all of our wonderful volunteers for everything they do for us!

Our Chat and Facebook Mods dedicate an extraordinary amount of time to providing a fun, educational chat. In addition to time spent online with watchers, they dedicate themselves to learning everything they can about bald eagles and their habitat, help keep me informed of important or extraordinary events, let me know when technology is going wrong, and bring their own ideas to bear on tools and content for followers! Our sites would not be what they are without them.

Our  Camera Operators and Video Makers share life in the nests with us. They give us extraordinary close-ups, interesting moments, and tours of the areas that shape the lives of the birds we watch. Thanks to them, we get to see and relive important events and cuteness overload close-ups, even when we aren't able to watch live!

Our Landowners share their wildlife and resources with us. We would not be watching eagles if they weren't willing to let us do so. Those with falcons on their properties watch nests, provide helpful information, and let us on to their land to band, survey, and put up boxes. They have been a critical part of peregrine falcon recovery!

Our Board is working on long-term goals and strategies. We would not have N2B or Decorah North without their direct help, and it has been wonderful to work with them as we do things now and prepare for our future.

Volunteers, I appreciate their dedication and talents more than I can say. As Bob would say "You ROCK!" Thank you for all you do.

Amy

Eaglet Growth and Development: Week Two

D24 and D25: 04/04/16

D24 and D25: 04/12/16

D24 is 15 days old today, while D25 turns 13 days old. The week-old difference between these two photos is striking. In their second week of development, the eaglets grew larger, gaining roughly two pounds between April 4th and April 12th. They experienced rapid growth in features like beaks, culmens, and footpads, replaced their white natal down with thicker grey thermal down, and began 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, roe (fish eggs), venison (aborted fetal deer), rabbit, squirrel, something that might have been a muskrat, waterfowl, and several other birds. D24 became proficient enough at shooting poop to christen the Poopcasso tree on April 5th, while both eaglets got in plenty of tussling and bonking play, alternately hitting, submitting, and quitting to cuddle in the nest cup, grow, and wait for more food to arrive.

Watchers have been asking why the Fort St. Vrain eaglets began wandering the nest so much earlier than the Decorah eaglets. While we don't know for sure, we suspect that temperature played an important role. Fort St. Vrain experienced unusually warm temperatures in late March and early April, and the leaves hadn't unfurled to provide shade for the nest. Cold is a challenge to eaglets under 10-15 days of age, but so is heat! With little ability to control body temperature and no way to lose heat except by panting, the eaglets did their best to retire to what little shade tree limbs and the nest itself offered. Once in the shade, they sprawled out as much as they could. Mom did her best to provide shade for the eaglets, moving from one to another and standing between them and the sun.  As alarming as it was to viewers, Mom's ploy worked and we didn't see quite as much wandering, at least for a few days, after the weather cooled down. 

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 the week, our little bobbleheads at Decorah and Fort St. Vrain will be almost a foot tall, while the eggs at Decorah North should begin hatching! 

Watchers have observed that different nests seem to have different 'parenting' styles: i.e., Dad may be more present at one nest than another, food may come in more or less regularly, and eaglets might spend more time alone. Many things influence nest life, including weather, temperature, food availability, predators, and the presence of other adult, sub-adult, and juvenile bald eagles. While eaglet growth and development occurs along a fairly predictable trajectory, local conditions can change the timing of events - something we've seen in Decorah, Fort St. Vrain, and the year we watched Eagle Valley. We are looking forward to hatch at Decorah North!

---

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.

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! I'd tend to think that visual acuity suddenly 'lit up' this week, leading changes in coordination as the eaglets began sitting up and moving around.

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
• 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.

Is the last egg going to hatch?

The last egg in the Original Decorah nest

As of this morning, the unhatched egg in Decorah is somewhere between 49 and 42 days old. Can it still hatch? Eagle eggs have hatched as late as 44 days after they were laid. If this is the last egg, we still have roughly two days in which hatch could occur. However, eggs have never hatched this far apart in Decorah before. Given the dates, it is possible that we've seen the hatch of eggs number two and three instead of eggs number one and two as we initially assumed. Roughly 3% to 12% of bald eagle eggs fail to hatch based on the studies I read, although some sources put the number a little higher, at 10% to 25%.

So why wouldn't the egg hatch? Eggs fail to hatch because they are either infertile or nonviable. Infertile eggs occur when the ovum is not fertilized before it begins its journey down the female's oviduct. We know that bald eagles copulate frequently before and during egg laying, which helps assure that sperm is present in the right place (the infundibulum) at the right time (when the ovum arrives).  Since female birds don't have a way to reject or stop the egg-laying process once it begins, incomplete, poorly timed, or insufficient copulation can result in unfertilized eggs.

A nonviable egg occurs when an embryo fails to develop properly and dies. This is mostly likely to happen within the first three days of incubation (embryonic organs fail to develop) or the last three days immediately prior to hatch (major organ failure becomes apparent or hatch starts but cannot be completed). Non-viability can happen for a number of reasons, including:

• Insufficient incubation. Incubation is fairly complex! Eggs must be kept at the proper temperature and humidity and turned regularly. Freshly laid eggs can spend time in the zone of suspended development (roughly 28.4 to 80.6°F) with no harm to the egg or embryo, but eggs must remain between about 99 and 104°F once development starts. Time off the eggs regulates humidity and helps keep pores from clogging. Turning or rolling the eggs prevents the developing embryo from sticking to the side of the egg, brings it into contact with fresh 'food' and important nutrients supplied by the yolk and white, and assures proper development of the membranes that exchange gas and protect the embryo from contaminants. 
• Piercing or cracking of the shell. If the egg shell is pierced or cracked before the embryo is fully developed, it will die. This can happen if the egg is jostled too vigorously, stepped on, or damaged or destroyed by an intruder - something that has been documented in many species of birds. 
• Insufficient nutrition. Given all that we've seen the eagles eat, this doesn't seem to be especially likely in Decorah. But if a female bird is insufficiently nourished before she begins laying eggs, her eggs won't have the nutrients needed to nourish the developing embryo. 
• Bacterial or chemical contamination. Although the embryo is protected by a shell and layers of membrane, contaminants can sometimes make their way into an egg and impede or kill the embryo inside it. 

We aren't going to attempt to retrieve the egg if it doesn't hatch - at least not while the birds are in the nest. Without opening the egg, we have no way of knowing why it failed. On one hand, the eagles spent a surprising amount of time off the first two eggs. On the other, studies in some species of birds indicate that infertility is more common than non-viability. Infertility is also more likely to prevail in first and last-laid eggs, which is unsurprising given the importance that timing plays in fertilization. 

What will happen to the egg? Different species do different things, but bald eagle eggs are commonly buried under layers in the nest, where they presumably break and decompose. Eggs may also be pierced or trampled as siblings grow and become more active. We will look for the egg if we go into the nest this fall. If we find it intact, we will turn it over to the USFWS for study. 

Will the next eaglet to hatch be called D26 or D27? This is confusing to followers who have seen nothing but production success. However, peregrine falcons aren't always successful and we don't count production until after banding. A falcon that makes it to fledge but dies soon after is still considered in production counts, but a falcon that dies before banding is not. If this egg doesn't hatch, the next living eaglet will be called D26. 

It's hard to believe that we could have an unhatched egg after so many years of success. How many times have we been worried about something only to have it all turn out right? But eggs don't always hatch and even excellent parents like our Mom and Dad experience failure. I'm glad we have D24 and D25 to watch this year and I look forward to studying the dynamics and rearing of two siblings, even though I wish there were three.  If we have a chance, we'll retrieve the egg for inspection and we will also review the video record to determine how much time was spent off the first egg.

Note: While I included contaminants on the list of things that can cause eggs to fail, my guess would be that this egg failed due to infertility (statistically more likely according to what I could find) or incubatory failure due to cold exposure.

Eaglet Growth and Development: Week One

Newly hatched D25, March 31st 2016

D24 is three days old today, sibling D25 is not quite a day old as I write, and D26 is still inside the egg. What can we expect in the first week of watching?

Weight Gain!
Like humans and other animals, growing nestlings have developmental milestones. The eaglets spend roughly the first week of their life gaining weight. They aren't able to thermoregulate yet, so depending on the weather and temperature, they may spend a lot of time under Mom and Dad. We'll see them eat, sleep, scuffle, and grow stronger as they interact with one another.  They will go from roughly 3.2 ounces - about the weight of 18 nickels - to roughly 16 ounces or one pound, increasing their weight five times over in just seven days.

Many structural features, including foot pads, tarsi, and hallux claws, won't start rapid growth until 10-15 days after hatch. But the hatchlings' mid-toes and culmen - the dorsal ridge of the upper mandible - are already growing longer! Food is the root of all else besides, so it isn't surprising that the culmen achieves maximum growth in the first ten days. I suspect that the mid-toe aids balance, a crucial element of sitting up and exploring the nest. While our eaglets won't truly stand on their feet until they are roughly four weeks old, they will begin to shuffle around the nest on their tarsi long before that.

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
• 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.