EAGLET GROWTH AND DEVELOPMENT

It has long been a dream of mine to collect a daily log of screen caps and videos that illustrate the growth and development of one eaglet from hatch through fledge, and which can serve as a framework for discussion of the many milestones in an eagle’s first 3 months of life.  This year, thanks to the superb camera setup at the Bluff City nest in Tennessee, operated by East Tennessee State University (ETSU), I have been able to realize this dream.

I have created a series of pages that includes a general introduction to eaglet growth and development, daily photos of young BC14 from hatch on 3/11/19 to fledge on 5/31/19, and a list of references.  I will be adding more pages to the series, covering specific eaglet features like feathers, feet, and various behaviors as it grows.

These pages would not have been possible without the assistance and support of Michelle France, camera operator and keen observer at the ETSU nests, who not only expertly zoomed, panned, and tilted the sometimes touchy cam, often catering to my requests, but also created a treasure trove of screen caps and videos every day which has been invaluable in my quest for daily shots.

I also must thank my long-time eagle-watching buddy Donna Young, whose careful observations over a decade have greatly enriched my understanding of eagle behavior.  Our countless conversations have helped shape this project and contributed enormously to the information I have gathered and presented.

The series I am launching today is found under the Menu item “Eaglet Growth” and so far includes:

More pages are in the works.

FEATHERS!

At the Bluff City nest in Tennessee this week (March 17-23, 2019) we are witnessing the three phases of feather development on a growing eaglet. This nest is live-streamed online by East Tennessee State University, and photos are used with permission. Link to the cam.

On Sunday the two eaglets (BC14 and BC15) were covered with their light gray natal down. These fluffy feathers, called “plumulaceous,” grow in tracts, or rows, that are layered more or less evenly across the skin. The feathers are thin and are not good insulators.

On Wednesday for BC14, and then on Thursday for BC15, we began to see the secondary down feathers emerge. This dark gray layer of down can appear as early as Day 6 after hatch. It is thicker and provides better insulation than the natal down, hence is sometimes called thermal down, as it helps the eaglets begin to self-thermoregulate. The secondary down soon will cover the natal down (but does not replace it because it grows from a different set of follicles). In this photo you can see the dark gray feathers appearing between the neat light-colored rows of natal down feathers.

Within a few days, even while the thermal down is still growing, the follicles that produced the natal down will begin to produce “pennaceous” feathers, ones with a central shaft that makes them stiff, and barbs and barbules that lock together. The shaft has blood vessels running through it as it grows, hence the name blood feather, sometimes also called a pen- or pin-feather (adapted from “pennaceous”). These contour feathers, which include the wing and tail flight feathers, will grow over several weeks to create a protective covering of the eagle’s entire body.

Pin-feathers begin to emerge around Day 12 after hatch, and today at Bluff City, right on time, BC14’s and B15’s wings show a thin line of dark brown feathers at the back edge of the wing. The flight feathers on the wings, the remiges, are the first to begin to grow because they are the longest and take the most time to reach their full length.

In this photo you can see the light gray tips of the natal down feathers that are being pushed out by the growing remiges.

So for the next few days we will be able to see all three types of feathers on the Bluff City eaglets: natal down, thermal down, and contour feathers. The contour feathers will eventually replace the natal down completely, leaving only the thermal down underneath. Contour feathers will appear slowly on the back, then the tail, shoulders, neck, head, sides, chest and belly, and finally the legs and feet. The feathers on the backs of the feet will be the last to grow in because the eaglets will only gradually develop the strength and balance to walk on their toes like their parents do, and feathers would not withstand the wear and tear of constant contact with nest materials.

Hatching Eaglet

Here is a rare bird’s-eye (pun intended) view of how an eaglet uncurls itself from inside the egg in the final stage of hatching. This video is of the hatch of BC14 on 3/11/19 at 10:32 at the Tennessee Bluff City cam, operated by East Tennessee State University.  I’ve slowed the stream to 10% of normal speed and added arrows to indicate the back, head, left wing, right wing, beak, tail, legs and feet, egg tooth (yes! the egg tooth!), umbilicus, and receding yolk sac of the new hatchling.  The eaglet has its back to us and its head is down, tail up.

COOPERATIVE BREEDING

Cooperative breeding is a mystery that scientists have spent decades trying to unravel. It occurs among not only birds but also mammals, fish, and even insects. It is not necessarily a mating system per se, but has more to do with how adults care for their young.

Bald Eagle nest video cameras have provided an opportunity for viewers to observe and document 2 instances of cooperative breeding: on Catalina Island from 1992-2007, and near Lock & Dam 13 on the Mississippi River from 2014 through the present (winter 2018). Published literature includes 6 additional reports of cooperative breeding at Bald Eagle nests, in Alaska, Minnesota, Connecticut, New York, Texas, and British Columbia.

Through several pages on this site I attempt to make sense of some of the mysteries of cooperative breeding and explore the behavior among raptors, including descriptions of each of the known cases of cooperative breeding among Bald Eagles.

Click here to get started.

HALIAEETUS LEUCOCEPHALUS

You know what it means.  (DO you know what it means?  The Latinized-Greekish universal scientific name for “Bald Eagle”?  Literally translated “Sea-Eagle White-Head”?  Term established in the 18th century by Swedish naturalist and taxonomist Carl Linnaeus?  Yes, you knew that.)

But can you say it out loud?  Without sneezing or coughing or mumbling?

I couldn’t either until I utilized the ever-handy Google to find someone to say it for me.

I found lots of someones.  Here’s a site that has Americans, Brits, Welsh, Australians, Canadians, Dutch, Chinese, Germans, Italians, Japanese, Poles, Danes, Russians, Spaniards, Turks, and yes, Swedes, and smart people of other nationalities saying it.

Go ahead.  Impress your friends.

HATCHING!

You know about the internal pip, the egg tooth, and the external pip. But do you know about symmetrical hatching, the complexus muscle, gas exchange via the chorioallantoic membrane, nidicolous chicks, and semialtricial species? If you’re interested in a slightly different presentation of hatching, check this out.

UPDATED EGG-LAYING CALENDARS

With the Bald Eagle egg season well underway and heating up, I have updated the monthly calendars of eggs laid at nests on camera to include data from the 2016-2017 season.  These calendars go back to 2007 when the first reliable observations of dates of eggs laid were recorded.  The season begins in Florida in November and stretches through April in British Columbia, Alaska, and the Yukon Territory.

Go here for the January calendar. From there you can navigate to other months.

“Totality”

I was in the path of the total eclipse of the sun on Monday, 21 August 2017. The birds stopped singing. Until just a few minutes before the moon completely eclipsed the sun, goldfinches, cardinals, and crows sang and called, an occasional Turkey Vulture soared overhead, and a flock of Barn Swallows chatted and flew over the fields. Two or three minutes before the total eclipse, the birds became still, while the crickets got louder.

I was in farm land – acres of green crops, small groves of trees along a creek, a couple of gravel roads, and only two other humans nearby.

The shadow progressed gradually over an hour or so. My Cheerios box with a tiny pinhole showed me the slowly growing crescent. The dimming of light was unnoticeable at first, then became unmistakable. My own shadow on the ground grew faint. At some point the screen on my cell phone became more readable than it is in broad daylight. The skies turned from bright blue with a few wispy clouds, to pastel blue, then to gray. The fields got darker, the trees less distinct. It didn’t look like dusk or dawn – the colors across the land were muted.

The total eclipse came abruptly. One second there was light, then all was in shadow, as if an overhead light had been switched off and only a weak night-light prevented pitch black. The dazzling corona of the sun shone around the edges of the moon, and the distant horizon, outside the umbra, showed some rosy hues. One bright star popped into view. Everything stopped, except the crickets.

The eclipse lasted about two minutes. Then all of a sudden the surrounding dimness was banished in a surprising wash of color as the surface of the sun emerged from behind the moon. The brightness was an illusion – only a sliver of the sun was showing, but it seemed as if the switch had been flipped back on. The restoration of daylight after the slow minutes of anticipation seemed quicker than the fading. Shadows reappeared everywhere – trees, farm buildings, road signs, fences, me. Crops and trees turned green. The sky was blue again.

Soon birds became active, chirping, calling, flying. The swallows took wing after insects, vultures lifted to the sky, a Carolina Wren sang, a Red-Tailed Hawk flew across the fields and perched atop a tall maple.

About five minutes after the sun reappeared, a rooster crowed. Then another, and then another.

I was struck by a feeling of bigness. The wide expanse of sky, in which two huge celestial bodies implausibly converged. Daylight turning precipitously into a vast eerie twilight. Hundreds and thousands of vertebrates and invertebrates unexpectedly moved to alter their behavior. Millions of people across the continent changing their normal routines in order to take in the other-worldly event. The astounding exactitude of the scientists’ predictions of times – to the second – and places – to the geographical degree and minute. The breath-taking rarity and the improbable opportunity afforded a small creature like me to be part of something so enormous. This was not a movie or a documentary or a news report. I was actually there. How cool is that?

I captured a few minutes of video, not of the sun but of the countryside, which to me was infinitely more interesting than the sun.  https://youtu.be/q23aTXWfVnc

When Will That Egg Hatch?

I’ve compiled and analyzed data from wild Bald Eagle nest cams from 2006-2016 concerning how long it takes for an egg to hatch.

In some ways the numbers support what veteran cam watchers have come to know about parents’ incubation behavior, delayed hatching of the first egg, and how close together hatches can occur in comparison to the minimum 3 days between egg-layings.

For instance, the first egg almost always takes longer to hatch than later eggs. Observations from these nests give us a pretty good idea of how much longer.

And hatches can occur as few as 4 hours apart. But for which eggs in a clutch?  The data tell us.

The data also show some more subtle facts, such as differences in hatch timings between a 2-egg clutch and a 3-egg clutch.

There are some unexpected numbers, such as the average time overall between when an egg is laid and when it hatches.  It’s 36.5 days.  Not 34 or 35.

In fact, the shortest hatch time on record at these wild Bald Eagle nests was 34 days 11 hours 1 minute after the egg was laid.  And that fast time is an outlier in the data.

The longest time on record was 40 days 12 hours 17 minutes.

And whether a nest is in a northern climate or a southern climate seems to make no difference in whether hatching is delayed.

Go here to take a deep dive into the data and my analyses.

Eggs, eggs, everywhere!

The 2017 breeding season is well underway, and as we approach the end of January it’s about to get crazier.  I have finished compiling comprehensive 10-year calendars of egg-laying dates at the nests for which we have reliable observations. Here are the calendars for January and February.  You will find the other months under the Bald Eagle Nest Cams menu.

Based on previous years, we might expect to see eggs between now and mid-February at the DNR nest in Minneapolis, John Bunker Sands Wetlands in TX, several nests on the Catalina Islands, Blackwater Wildlife Refuge in MD, Upper Mississippi River Refuge in IL, nests in TN and DC, Turtle Bay nest in northern CA, Lake of the Ozarks in MO, Davenport IA, and nests in Pittsburgh and at Duke Farms in NJ.

We’re also going to start seeing some more nestlings hatch.

As the title of this post suggests, these few dozen nests on cam are a tiny fraction of the Bald Eagle nests across North America where courtship, nest-building, egg-laying, and hatching have gotten well underway. For another year running, the population of Bald Eagles is about to surge.

Buckle up.

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