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[tulsaducati]

We are restarting our Bald Eagles Fact of the Day thread; had some technical issues with it and are hoping to get everything going again.  We are very sorry for the disruption!

[tulsaducati]

With the severe weather and big weather changes, we get a lot of questions about how the eagles manage staying safe and warm (or cool). Stalmaster says that eagles belong to a category of "regulated heterothermy" which allows their temperatures to fluctuate within a narrow range. Body temperatures of bald eagles range from 101.84 degrees Fahrenheit at night to 105.26 degrees Fahrenheit during the day to 106.16 Fahrenheit during flight. With body temperatures lower at night, they can minimize heat loss. Maintaining internal temperature is critical. In hot weather, without sweat glands, they pant to reduce body temperature. In the cold, the base layer of thermal down, which we are seeing come in on DH2 now, insulates the body, but the eaglet must still be protected from wet weather until the waterproof plumage comes in. Once the feathers are present, the eagle can manipulate the feathers to provide an extra level of insulation, by creating a warm air layer between the down and the feathers.

[oregonian1944]

The average rate of weight gain for a nestling prior to fledge varies but may be as much as 1 pound every 5 days. The largest weight gains are early in the nestling period. Between the ages of 18-24 days the eaglet gains about 4 oz. per day, more weight than at any other stage of development. So DH2's fastest rate of weight gain is coming up very soon. Many physical changes will also be taking place. Thermal down will be coming in so he is able to self-regulate his body temperature (thermoregulate), however, he'll not yet be waterproof.

[Bob1603]

In his book The Bald Eagle - The Improbable Journey of America's Bird - author Jack E.Davis writes about a Fish and Wildlife bald eagle census report completed in 2021. On the basis of aerial surveys from the previous two years, researchers calculated the bald eagle population in the lower 48 states had quadrupled during the previous decade.  Nesting couples totaled more than 71,000 and individual eagles well over 300,000.  Alaska's bald eagle population was put at over a conservative estimate of 70,000.  Canada had approximately the same as Alaska. To quote Davis "It would not be a stretch to say from coast to coast and from northern Canada to northern Mexico, five hundred thousand (bald eagles) occupied their indigenous  lands." 

The comeback of the American Bald Eagle has been truly remarkable.

[pelmomma]

An eagle can keep its body temperature within certain boundaries, even when the surrounding temperature is very different: thermoregulation!   Thermal down has very good insulating qualities and by 15 days old the chicks are typically able to thermoregulate on their own.  Parent eagles can be absent from the nest for slightly longer periods of time, although they are still close by and protective.

At 2 weeks of age the nestling should instinctively back up to the edge of the nest and defecate over the side.

[glogdog]

Odd as it may seem, birds do not instinctively recognize others of their species as being the same as themselves.  Instead, as chicks they "imprint" on whatever large, moving, vocalizing object cares for them. In the wild, this is invariably their parents, and the nestlings develop the correct self-image for their species.  It is this image that will eventually determine their choice of a mate. They also appear to imprint on the same kind of nest sites in which they were raised, and in a larger sense may imprint on their parents' habitat.

[pelmomma]

Between the ages of 18 and 24 days the eaglets gain about 4 ounces per day, more weight than any other stage of development. 

While the sexes are initially the same size, sexual size dimorphism begins to appear in some variables after 20 days of age. With one eaglet, of course, we have no frame for comparison.  So guess away!

[pyrmum1]

There are several stages of growth for eaglets:  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, foot pads, 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.

[tulsaducati]

Today DH2 is right at 25 days old; we're in the growth spurt that includes beaks and feet growing rapidly, talons turning from beige to black and lengthening. The thermal down gets even thicker, improving the ability to thermoregulate.  Wing primary and covert feathers start lengthening and pushing out the natal down. We'll start to see contour feathers on the back, shoulders, legs, and breast. We should see DH2 standing on his feet more, stretching, rousing, and maybe casting a pellet. Exploring the nest will cause some palpitations in we human watchers, as he/she will spend more time near the rails. For more details, check out Elfruler's excellent website: https://www.elfruler.com

[Iriscats]

Since we should be seeing this behavior from DH2, thought I would share what to expect. Casting a pellet: Casting is a round or oblong wad of feathers, fur, and bones which are left after the nutritious parts of a meal are digested. This can appear to be concerning for those who have not seen it before. The bird extends its neck, arches it, and wrenches it down, may also shake its head violently and appears to vomit. Birds who successfully bring up a pellet are exhibiting healthy, normal behavior. Also, the pellets seldom contain fish bones, because they are highly digestible.

[littlebittykitty]

 A bald eagle’s feathers are not only important for flight, they also help regulate body temperature, are useful for territorial, social and courtship displays, help keep certain areas of the body clean from debris and transmit information to nerve receptors in the skin (e.g. wind currents).  Bald eagles have approximately 7,000 feathers.  Their feathers weigh twice as much as their skeleton (which weighs about half a pound).  Thirty of a bald eagle’s feathers weigh about the same as a penny (.088 ounces).  Feathers protect an eagle from the cold as well as from the sun by trapping layers of air.  To aid in maintaining its body temperature, an eagle changes the position of its feathers by ruffling and rotating them so that air pockets are either opened to the air or drawn together to reduce the insulating effect.  Its feathers allow bald eagles to live in extremely cold environments. 

[pelmomma]

Various search and attack behavior patterns are basically instinctive for eagles, and appear in a variety of recognizable forms such as the glide attack.  But instinct alone cannot prepare for the wide variety of prey they will encounter, or the prey’s evasion tactics, or problems imposed by terrain. 

So the bird has to learn these through experience and modify the attack style as appropriate.  It also learns to improve its flying skills, its footing ability, and its basic attack strategies. 

The more specialized a species is, the more its hunting behavior is governed by instinct.  The more of a generalist or opportunist a species is - such as our bald eagles - the more its behavior is shaped through learning.



[littlebittykitty]

You may notice DH2's wings drooping as his feathers grow in.  This is caused by the blood supply in the growing shaft of each feather, which makes them heavy.  After the blood supply receded and the feathers are hard-penned, this will go away. 

You may see the feathers flash blue in the sunlight while they still have a blood supply.  Watch closely to see this.

[oregonian1944]

DH2 is approaching 5 weeks old - we can expect him to stand upright, begin to scream loudly and maybe attempt to tear his own prey. He will measure approximately 2 feet from head to tail and weigh around 6 pounds. His early plumage is visible through his 2nd down (thermal) and at this early stage can be referred to as a Juvenile. He will be seen pruning regularly now which removes dirt, smooths his feathers and distributes oil from the uropygial gland near the tail which helps to keep the feathers healthy. And wait, that's not all - he will begin vigorously flapping, hopping and moving around the nest - this we often call wingersizing.  So much to look forward to as we watch him continue to grow and gain more strength.

[Iriscats]

Michigan did a study of 1,490 bald eagles and deaths by trauma from 1986 to 2017. Vehicle collisions were responsible for 66.2% of female deaths, and 68.3% of male deaths, making them the biggest single killer of bald eagles overall. 518 females and 544 males died of car trauma.
Franson and Russell 2014

...The high number of vehicle fatalities may be exacerbated when roadside conditions prevent escape routes. In short, a lot of carcasses are available in October-December (rut-deer acting crazy) and Feb-March (or whenever the snow melts).  Eagles compete for them. This doesn't go well for them because:
-They aren't especially afraid of cars and also may not be able to judge how fast a car is approaching.  (There is a lot of argument about this since some birds can judge the speed).
-They are less likely to leave prey if they are hungry or other eagles are in the area.
-They aren't especially maneuverable or quick. They take off in a very straight line, can't change direction or trajectory quickly, and take some time to get off the ground.
-Trees, fences, houses, buildings, hedges and other obstacles might force them to take off into roadway.

So, if you ever see a bald eagle on the road, slow down and give it as much space as you can, safely.
Amy Ries 2023