Raptor Resource Project Forum
Chat Moderators => Decorah Eagle Mods Want You To Know -- Eagle Education => Topic started by: tulsaducati on April 19, 2023, 09:24:14 AM
-
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!
-
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.
-
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.
-
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.
-
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.
-
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.
-
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!
-
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.
-
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
-
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.
-
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.
-
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.
-
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.
-
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.
-
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
-
5-9-23: Hard to believe, but DH2 is already 32 days old. We're seeing lots of changes now, with the juvenile feathers coming in on the wings and tail, covert feathers covering the base of wing and tail feathers, and contour feathers appearing on DH2's back. We've often been asked about how the feathers develop, and particularly if the juvenile feathers are produced from the same pores that produce the thermal down. Reading through Amy's blog, it's a far more complicated subject than I thought! It turns out, feathers do not sprout from pores that produce down. Complex feathers grow from follicles that become active after hatch. Juvenile feather growth really takes off at about 35 days, so we should see some exciting feather changes soon. Here's a link to Amy's blog on the subject: https://www.raptorresource.org/2023/05/01/from-bobble-heads-to-eaglets-natal-down-thermal-down-and-flight-feathers/
-
Coming to Terms!
Digitigrade - animal or bird that walks on its toes (digits) as opposed to -
Plantigrade - foot flat on the ground (humans).
Eagles are digitigrade (what a great vocabulary word!). We see that starting in week 4 DH2 is gaining the muscle strength to stand. The nest is certainly not a very firm, stable surface to practice walking but the challenge will actually help them strengthen those leg muscles. This will enable DH2 to "prance" about on those huge toes to explore his/her beautiful home high up in the cottonwood.
and here is a link for everything you could possibly want to know about bird feet and legs!
https://en.wikipedia.org/wiki/Bird_feet_and_legs
-
Flap, Flap, Flap! We’re starting to see DH2, in the 5th week of life at the Decorah Eagle’s nest, begin to flap those growing wings. “Wingercizing” as we call it helps to strengthen the wing muscles. There are about 50 different muscles that control the wing movements, but the Pectoral muscles and the Supracoracoideus muscles, are the primary engines of bird flight. The Pectoralis major is the primary depressor of the wing in downstroke. The Supracoracoideus is the primary elevator of the wing in upstroke. Here is a neat video showing how they work: https://youtu.be/aFdvkopOmw0
-
May 13, 2023: DH2 is 37 days old! According to Dr. Bryan Watts, T90 (the time required to reach 90% of the terminal or final weight) is reached between the age 36 and 42 days, depending on the gender. The smaller sex (the male) is characterized by earlier development of feathers, faster attainment of asymptotic size (size that nears the peak of the growth curve) and earlier flights from the nest. Most of an eaglet's weight gain, relative to its overall body weight, occurs early on. We've had lots of discussion about the sex of DH2, we would all love to know whether we have a boy or a girl. While both sexes are about the same size at hatch, the sexual size dimorphism begins to appear in some variables after 20 days of age. Bortolotti found sexual dimorphism for bill depth to be present at 20-24 days, and for foot pad between 25-29 days. These variables level off between 40-45 days. Although we have some clues about the possible sex of our eaglet, without another eaglet in the nest for comparison, we'll just have to keep wondering! As we continue to watch DH2 standing tall beside his parents, it's apparent that we are at or near 90% of his or her ultimate size.
-
Covert feathers cover the bases of the flight feathers. They cover the leg from the upper leg to the abdomen on both the dorsal and ventral surfaces of the body and help streamline the shape of the wings and tail while providing insulation.
-
Most of us will agree that the tail of an eaglet is just about the cutest thing ever. So let's talk about the structure of the tail.
There is a bone at the posterior end of the spinal column in birds called the "pygostyle" which consists of several fused caudal vertebrae and supports the tail feathers (number 17 in the photo). It is the main skeletal base of the "uropygium", the posterior part of the body from which the retrices, or tail feathers grow. The uropygium is the fleshy and bony protuberance at the posterior extremity of a bird's body that supports the tail feathers. Colloquially it is known as the bishop's nose, parson's nose, pope's nose, or sultan's nose.
-
Birds have large brains relative to their bodies and that account for about 9% of their body mass. Many types of birds, particularly hunters such as bald eagles, show complex intelligence and learning abilities.
The optic lobes and the cerebellum (which helps coordinate muscles in flight) dominate the midbrain. The two optic lobes are huge in relation to the rest of the brain.
The olfactory lobes are relatively small in most birds, suggesting a poor sense of smell as with bald eagles. Some birds, such as vultures, do have a well-developed sense of smell.
-
We have often observed HM bringing in talons full of nesting material prior to forecasted weather changes. Here is an explanation as to why or how she can sense changes in the weather.
A bird's skin has sensory nerve endings that detect heat, cold, pressure, and pain. Touch is an important sense to them, especially in flight. They are very sensitive to changes in air temperature, pressure, and wind speed. These changes are transferred down the feathers to nerve endings in the skin. Filoplumes around the bases of major flight feathers have sensory corpuscles around the base of each feather shaft. As the remiges are moved during flight, the filoplumes assist the bird in judging what position its flight feathers are in and gives feedback as it shifts the position of its feathers. This allows birds to feel despite their thick covering of feathers.
-
Eagles, like all birds, have superior color vision. They see colors as more vivid than we do, can discriminate between more shades, and can also see ultraviolet light — an ability that evolved to help them detect the UV-reflecting urine trails of small prey. In addition to the wider spectrum of color vision, we all know that eagles have much sharper visual acuity. Their retinas are more densely coated with light-detecting cells called cones than human retinas, enhancing their power to resolve fine details just as higher pixel density increases the resolving power of cameras. They also have a much deeper fovea, a cone-rich structure in the backs of the eyes of both humans and eagles that detects light from the center of our visual field. Some investigators think this deep fovea allows their eyes to act like a telephoto lens, giving them extra magnification in the center of their field of view. A big thanks to our deeply loved and sadly missed TX_Ninja, who taught us much about eagle eyes, and many other things. Fly high, TX.
-
At 12-13 weeks old, an eaglet's flight feather growth is developed well enough to leave the nest. Fledglings will begin to hone their flying skills and landing techniques as they begin the process of learning to find and kill prey. They will still depend on the parents for food for several weeks, and typically stay close to the nest tree as they learn how to forage for food. This period is used to complete feather growth and to develop muscle strength. Young eagles learn by watching their parents, and by practicing instinctive behaviors. Juvenile skills are perfected by trial and error, and within about a month after fledge, they will have mastered the art of soaring. By late summer, juvenile eaglets will be flying well outside the nest territory and learning to hunt and search for their own food. A juvenile eagle is nearly self-sufficient at an age of about 16 weeks. Eagles hatched in April will likely leave their parents' home range in September.
-
"The ten weeks of nest life can be divided into three stages: eyas, this is derived from the French niais, meaning "fresh from the nest " and which refers to the first three to five weeks when the eaglet is covered with down, needs to be brooded frequently, and is unable to stand and feed itself; ramage, from the French word of the same spelling meaning "wild" or "of the branches," when the eaglet becomes covered by feathers, needs to be brooded only in harsh weather, and learns to stand up, hold food, and feed itself; and brancher, which for eagles is the one-week period near the nine- to ten-week age when they move out to the branches to strengthen their leg muscles and fine-tune their balance."
Excerpt taken from A Season with Eagles by Dr. Scott Nielsen.
-
DH2 has demonstrated this week that he can self-feed, but it will be a long time before this young bird becomes proficient.
As we’ve seen, DH2 is also almost as large as his parents. By 7 weeks of age, young eagles have attained almost their full fledging weight and very much look ready to fly. But his tail feathers have only started to lengthen, and his wing feathers are well below fledging length.
We’ll see increasing bouts of wingercizing in the coming days, followed by the excitement of hovering.
-
A bird has some 175 different muscles controlling the movements of its wings, legs, feet, tongue, eyes, ears, neck, lungs, sound-producing organs, body wall and skin. Collectively, the muscles are concentrated near the bird's center of gravity. Muscles are used for motion and balance and are the primary organs of heat production in the avian body.
The muscles that surround the cervical spine are numerous and complex. They both support the cervical vertebrae and provide precise control over movement such as helping the head and eyes move rapidly. Birds also need their long necks to reach and groom their feathers. There are many thin overlapping sheets of muscles and except for the long dorsal and ventral midline muscles, are no longer than a third of an inch. The image below is a rough diagram of major muscles of the bald eagle.
-
Birds have the keenest vision of all vertebrates. It is the most important sense for the bald eagle. Bald eagles are diurnal (active during the day)
Their eyeballs are almost as large as humans, but they are fit so tightly into their heads that they can barely turn them in their sockets. In order to see in all directions, they have to tip or turn their head. Fortunately, their necks are very flexible, and can rotate their heads 270 degrees, unlike humans who can only rotate their heads 180 degrees.
The position of the eyes allows both monocular vision where both eyes operate somewhat independently to see objects to the side, and binocular vision, where both eyes focus on an object directly in front of the head just like humans. Binocular vision gives them extremely accurate depth perception that allows depth of field-an important asset for a bird that has to pinpoint prey from great distances in order to catch it with their talons.
An eagle bobs its head up and down and from side to side in order to triangulate the distance to its prey (triangulation means measuring something using trigonometric relationship between pairs of sides and angles of triangles). In effect, the eagle can use his eyes like a range finder. Not only can it spot prey at great distances, it can also judge how fast to fly to catch prey.
A bald eagle looking at a football field (or fish or other prey) would be able to see it from 32 football fields away, or just about 2 miles.
If humans had the vision of an eagle we could see a pin lying on the shoulder of a road while driving 65 mph!
-
The calamus (sometimes referred to as the quill) is the part of the shaft closest to the bird’s body. It is hollow and doesn’t contain any vanes. The distal end of the shaft is called the rachis. It is solid and is the area to which the vanes are attached. The flight feathers of the wings are called remiges and are of two kinds: primaries and secondaries. Primaries are 10 in number and are those finger-like feathers that are attached from each wrist to the wing tip - they aid in providing forward lift or thrust in flight and can be adjusted individually to help in stability and maneuverability during flight. Secondary flight feathers, or secondaries, are mid-wing and are 16 in number.
-
DH2 is fast approaching 8 weeks old and you can see he is already well-feathered and is about 90% of his mature weight. You may see his wings drooping at times because his developing feathers are blood filled which can cause the wings to be heavy. Now is the time when we may see him begin to practice "hovering" (sustaining air briefly but remaining above the nest) and practice landing. He has already developed the aggression for grabbing or stealing food from the parents. This is the time we will see lots of activity while he is learning many things, running, jumping, trampling, wingersizing, hovering, etc. Sit back and enjoy watching him. (Note: we don't know his gender, but I always refer to our DH2 as he)
-
Eaglets about 60 days old are well feathered, and have achieved more than 90 percent of their mature weight. Their growth is so rapid that a standing eaglet may occasionally droop its wings, since the developing feathers are blood filled and the wings can be heavy. The entire set of primary and secondary feathers is growing at the same time. We have seen our eaglet's hop-flap technique improving daily, getting both feet off the nest. https://youtu.be/6xj0nN3_8hc
DH2 will soon practice "hovering" (which is sustaining air briefly but staying above the nest - think helicopter) and practice important landings. Wing flapping and hovering also strengthens their pectoral muscles necessary for flying. Other exercises they can perform are treading, trampling, and prancing which might help them later in subduing prey.
-
Birds vary greatly in their cognition skills, in ways that affect an individual bird's survival and reproduction. Large brain sizes in bald eagles (9% of their total body mass) require longer incubation periods to mature. Foraging skills, breeding, parental care, long life span and even play behavior all correlate to the brain sizes and cognitive abilities of birds
-
A bald eagle’s hearing is not quite as highly developed as its vision, but still extremely sensitive. Ears are simple openings in the skull below and behind the eye. They are only visible in the first week or two after hatch and are then covered by sparse feathers called ear coverts or auricular feathers. These auricular feathers will protect the bird's ears in flight. The muscles that anchor these feathers form a shallow funnel which directs sound into the ear.
The ear opening leads to an eardrum or tympanic membrane that covers the middle ear. Sound waves are transmitted by the eardrum to the inner ear, also known as the labyrinth, where they are transformed into nerve impulses that are transmitted to the brain. Semicircular canals in the labyrinth also assist in equilibrium.
Scott Nielsen makes the point that the bald eagle never reacts just to a sound but always follows any noise it hears with a close visual examination of where the sound came from—if the visual observation confirms a threat, they will leave the area.
-
Fishing
The bald eagle is also referred to as a fish eagle because some studies show an average of about 56-90% of its diet will consist of fish. Bald eagles use a number of techniques to search for and catch prey. When a fish is sighted, they will usually descend quickly and smoothly from their perch. The eagle starts at a high angle and has an idea of the location of the fish. As it gets closer, it glides in at a bend that becomes steeper until it nears the fish. At the water's surface the eagle will reach a foot (or both feet for a larger fish) and carry it off. Occasionally when capturing a larger fish, the eagle will plunge into the water and may not be able to take flight with its prey. In such an instance, it will tow the fish to shore swimming awkwardly, stroking the surface of the water with its wings while pulling the fish with its talons to shore. Another less common way to fish is wading into shallow water where smaller fish are available. According to Mark Stalmaster in his book, The Bald Eagle, an eagle will wade up to its belly, submerge its head and strike with its beak. "Generally they can carry approximately 4 pounds of weight in their talons, but I will delve deeper into that on another Fact of the Day"
Eagles more easily recognize fish that are upside down (white side up). White side up fish are more quickly spotted and caught as they are more visible to eagle eyes.
Young eagles are much more likely to "catch" fish that have washed up on shore or fish that are floating rather than swimming.
-
The nervous system is divided into 2 main parts-the central nervous system (CNS) and the autonomic nervous system (ANS). The CNS is responsible for voluntary reactions of the body, such as movement or flight. The ANS is responsible for the coordination of involuntary actions of the organs, intestines, blood vessels and glands. The primary function of the nervous system is to integrate the functions of the body. Proctor & Lynch state that the central nervous system receives stimuli from within the body and from the outside world through the sense organs and peripheral nervous system. After processing the information, the central nervous system sends motor signals through the spinal cord and peripheral nervous system to control the bird’s movements and reactions to the world around it.
-
The next milestone we are watching for should occur soon, around 9 weeks of age. Branching is defined as a direct flight to another branch (vertical or horizontal limb) in the nest tree…not a walk up, not a hop-flap, but a flight. A little wind assist is fine, but the prerequisite is wing powered flight. Scott Nielson defines this term as "the one-week period during the nine-to-ten-week age when they move out to the branches to strengthen their leg muscles and fine-tune their balance." He also says they use this developmental phase to strengthen their grip which will be important not only for perching and landing successfully after flight, but also for grasping their own food.
-
Here is some Eagle terminology information as it pertains to the various stages of growth and development: Eaglet - anytime from hatch to about 10 weeks after leaving the nest; Hatchling - 1st week; Nestling - after 1st week until fledge; Fledgling - While perfecting flight – after taking their first flight; Juvenile - when the 1st coat of feathering grows in and for the 1st year; Immature or Sub-adult - after 1 year until adulthood. Some of these periods of growth can overlap.
-
Air pressure is what enables a bird to fly. Air passing over the top of the wing must travel faster than air going beneath it; therefore air pressure decreases above the wing generating lift. In order to have air moving over and under the wing, the wing must be moving. This is called thrust. Thrust is created when birds flap their wings using their strong breast muscles.
Tails are important to bird flight and is comparable to rudders of ships and boats. The tail feathers help the bird steer and maneuver while flying, as well as providing stability as they take off and land. By twisting the tail, they can change direction mid-flight. By flaring out the tail, it helps the bird to slow down, creating drag and decreasing the bird's velocity.
-
Raptors’ memory is generally very good and aids birds in migration. Like a lot of humans,
raptors’ comprehension, and ability to recall is better for sights than for sounds-but their
sharpness of vision and ability to recognize things is much better than ours.
Nick Fox’s observations on memory relate mainly to trained raptors. He tells a wonderful story
about an old goshawk that he had trained who used to sit silently on her perch outside in his yard
surrounded by his students. As soon as she saw part of Fox’s head appear in the window, she
would call to him immediately. He also says that trained hawks will recognize their owners after
more than a year of absence and remember the meaning of the lure used as bait as well as the
hood the trainers use.
-
As in mammals, a bird’s skin has sensory nerve endings that detect heat, cold, pressure, and pain. Birds don’t rely on touch as extensively as humans, but it is still an important sense to them, especially in flight. They are very sensitive to changes in air temperature, pressure, and wind speed. Those changes are transferred down the feathers to nerve endings in the skin. Filo-plumes are numerous around the bases of major flight feathers that have sensory corpuscles around the base of each feather shaft. As the remiges are moved during flight, the filo-plumes assist the bird in judging what position its flight feathers are in, and give it feedback as it shifts the position of its feathers.
-
Dispersal is defined as the purposeful movement away from population centers that serves to separate individual members of avian populations in one area. Juvenile bald eagles generally leave their natal nest area and begin their adventure when they are no longer dependent on their parents for food. The results are a mixing of individuals hatched at different locations.
Dispersals are often undertaken by recently fledged birds and serve to increase population ranges and reduce population densities so that the birds that disperse are more likely to survive and reproduce than those who do not disperse.
-
Triangulate means to determine a point in three dimensional space. Raptors do this by bobbing their head or moving it in circles to determine how far away an object is.
-
There are 3 areas of concern to a breeding pair of bald eagles, the nest site, the breeding/nesting territory and the home range. The breeding/nesting territory is about 1-2 square miles and the home range territory is about 10-15 square miles. The more densely populated the area is, the smaller the range is. Eagles will defend their breeding territory from would-be intruders, with the nest site being their primary focus. Gary Bortolotti points out that spending a large portion of their day perched at the top of a tall tree, with bright white head in full view, serves as a signal to unwanted visitors. A mated pair will often perch side by side facing in opposite directions for the purpose of territory defense. Eagles search for food in their home range but they do not defend it.
-
Birds do not have vocal cords, but rather vocalize with a muscular organ, the syrinx, located where the trachea divides to enter each lung. A stiff membrane protrudes into the syrinx and produces sound when it vibrates, similar to a reed in a clarinet. Muscles along the outside of the syrinx adjust in length and tension to produce different pitches. A raptor’s syrinx is simple and does not produce the variety of sounds as a songbird, for instance, which may have numerous thick strands of muscles at varying angles around the syrinx.
-
Many of you know or have heard about the Cornell Lab of Ornithology at Cornell University. For your reference the Lab has a phone app that will help you identify over 1,000 songbirds as well as more than 7,500 birds you can ID through photos. Here is a description about the app from the Lab's homepage:
In 2014 we introduced our free free Merlin Bird ID app, designed to help people answer their #1 question: What’s the name of the bird I just saw? The app works amazingly well thanks to its “smart” approach: users answer a few simple questions or snap a picture and then the app uses eBird data to present a short list of possibilities tailored to your location and date. More than a million downloads later, the app is more powerful than ever—it now covers more than 37,0500 species across 40 countries, and it can even ID birds in photos., and now it can even ID birds singing around you!
Here is a link to that webpage.
https://www.allaboutbirds.org/news/get-more-from-merlin-bird-id-with-these-powerful-features/#
-
Eagles hatched in April will likely leave their parents' home range in September, traveling irregularly and unpredictably. Until then, they generally stay within a mile or so of their natal nest. Stalmaster tells us that through their 20th week, seven weeks after fledging, most young are still within approximately .9 miles of the nest. On average it takes about 4-12 weeks for young eagles to start hunting successfully. Expert fishing and hunting skills probably take years to develop.
-
At 12-13 weeks old, the fledgling's flight feather growth is developed enough to leave the nest. Some researchers have estimated the wing and tail development and growth at about 95% during this stage. Similarly, their flight muscles don't fully develop until after they've started flying. Scott Nielsen states that up to five weeks is required from the time the eaglets leave the nest until their flight feathers are completely formed. This period is used not only to complete feather growth, but also to develop muscle strength and improve flying skills.
-
A review of the feather development in eaglets. As Glogdog stated in the previous FOD, flight feathers have still not completely developed by the time the eaglets fledge and will have about another five inches to grow. Feathers grow from the tip first, with the base of the feather being the last to develop. At this time it is somewhat fragile and susceptible to damage. Once the feather has completed growth, the feather shaft hardens (known as hard-penned) and ligaments and tendons have grown and connect the feather to the wing bone, making for a much stronger, sturdier flight feather for our fledged eaglet!
-
Along with flight feather growth, the last stage of development for the nestling is neurological and behavioral, learning coordinated movements. Typically fledge occurs between 10 to 13 weeks of age. Researcher Gary Bortolotti stated that males 1st flight average 78 days (68-84 day range), females 1st flight average 82 days (78-88 day range). DH2 may venture out to a branch, or may fledge without ever branching.
When the chicks are young, peak energy demand occurs in the late stage of rapid growth when metabolic demand is high. After terminal size is reached, energy demand declines to maintenance alone, and resembles that of the adults feeding schedule. It has been said that parents will disallow food for a few days around this age to encourage fledge, however some researchers state that this is not true, and the eaglets fledge when they feel confident in doing so.
-
The wings of an eagle are approximately 6 to 7 feet from tip to tip fully stretched.
The pectoralis major muscles and the supracoracoideus muscles beneath them account for between one-fifth and one-third of the total body weight. These muscles are the primary engines of bird flight. Birds use their strong breast muscles to flap their wings and give them the thrust to move through the air and fly.
Eagles have a greater amount of wing loading (the weight carried by the surface area of the wings) than most other birds. Adult wing loads are about 15% greater than those of young eagles. This is because adults weigh more, and their wings are narrower. Immature eagles, with their relatively larger wings, flap slower than adults. That changes progressively as an eagle ages. Adult wings are adapted for speed and attacking, whereas the wings of young eagles are adapted for soaring and lift.
-
The position of the eagles' eyes allows both monocular vision where both eyes operate somewhat independently to see objects to the side, and binocular vision, where, like those of humans, both eyes focus on an object directly in front of the head. Binocular vision gives them extremely accurate depth perception and allows for precise depth of field - an important asset for a bird that has to pinpoint prey from great distances in order to snatch it with their talons. In addition, their eyes have two fovea, or pits or funnel-like spots on each retina that are the points of sharpest vision. One faces forward and the other is directed sideways enhancing their vision.
-
Occasionally we see DH2 sporting some fuzzy “bling” on the beak. That is simply some of the remaining white natal down. Most of the natal down is gone but Dr. Scott Nielsen in A Season with Eagles reminds us that during the last two or three weeks (or days?) before an eaglet fledges s/he will spend time preening out the last of the down, in the process inadvertently indulging in a little self-decoration.

-
NEST-VISITING ETIQUETTE
Federal guidelines mandate that humans stay 330 feet away from nesting bald eagles and individual eagles who may be perched on a tree or standing on the ground. That being said, it is
important to stay as quiet as possible, move slowly, and do nothing that might stress the birds. Do not feed the eagles and keep the area free from litter. This includes leaving food on the
ground. These birds are wild and should not become dependent on humans. Do not approach the eagle if it is on the ground, and don’t attempt to follow it if it flies away. Respect landowners and do not trespass.
Disturbance of nesting eagles can vary from minor to major and is defined as anything that might change an eagle's behavior. If it stops what it is doing (preening or feeding its young for example) that is a sign it has been disturbed. Eagles seem to be most alarmed by visual disturbances. Providing a visual buffer works well while observing eagles. Cars make excellent blinds. Major disturbances may cause the birds to abandon their nest or cause young eaglets to flush from the nest before they are ready to fly. While some eagles may seem to be habituated to human activity, it is unknown what the cumulative effect of minor disturbances might have over time.
In Just Eagles, Alan Hutchinson published the very helpful North American Nature Photography Association’s “Principles of Ethical Field Practices” that give suggestions on how people can
enjoy nature in a way that protects the animals and environment in which they live. Binoculars and/or cameras will afford you the best view while visiting a nest.
-
FLIGHT
An adult bald eagle flies (cruising speed) at approximately 30-35 miles per hour and can dive at a speed pf up to 100 miles per hour. Measured flight speeds of migrating eagles were recorded at between 36-44 mph (Broun and Goodwin 1943) In flight, they can reach an altitude of some 10,000 feet.
When a bald eagle soars, it rides upwelling warm air currents or thermals; in so doing,
it uses minimal energy of its own. Bald eagles also utilize obstruction currents, which are produced when wind currents are deflected by mountains, cliffs or tall structures.
There are three flight patterns used by adult bald eagles: 1) ascending in a thermal, then gliding downward which can take them several miles before they need to find another thermal: 2) circling steadily downward using a "street of thermals," which is a series of rising air masses that often result from a single strong thermal: 3) using rising air currents generated when winds sweep against a cliff or other raised feature of the local terrain.
-
Feathers of the wing and tail of fledglings are longer than those of adults, but it still takes approximately five weeks from fledge to fully form flight feathers, develop muscle strength and improve flying skills. According to Gary Bortolotti in The Bald Eagle, juvenile primary feathers are about 8% longer than adult, secondary about 13% longer and tail feathers about 23% longer. As an eagle matures, its wings become shorter and narrower and its tail shorter with each successive molt. The theory is that the fledglings’ greater wing area makes it easier for them to be carried aloft in a thermal or updraft. It also allows them to fly slower and to soar in tighter circles for smaller thermals than the more experienced adult eagle.
-
After the eaglet leaves the nest, she/he will begin to hone flying skills and landing techniques, and begin the process of learning to find and kill prey. They will still depend on the parents for food for several weeks. That dependency will gradually diminish as they learn to forage. Because fledglings are poor hunters, they will likely scavenge on carrion for a time. Eaglets typically stay close to the nest tree during the first few weeks after fledging, but they eventually begin to explore areas further away. Scott Nielsen states that up to five weeks is required from the time the eaglets leave the nest until their flight feathers are completely formed. This period is used not only to complete feather growth, but also to develop muscle strength and improve flying skills.
-
Young eagles learn by watching their parents, and by practicing instinctive behaviors. Juvenile skills are perfected by trial and error. Within about a month after fledge, they will have mastered the art of soaring. By late summer, these juvenile eaglets will be flying well outside the nest territory and learning to hunt and search for their own food. A juvenile eagle is nearly self-sufficient at an age of about 16 weeks.
Eagles hatched in April will likely leave their parents' home range in September, traveling irregularly and unpredictably. Until then, they generally stay within a mile or so of their natal nest. Mark Stalmaster tells us that through their 20th week, seven weeks after fledging, most young are still within approximately .9 miles of the nest.
-
Mark Stalmaster, in The Bald Eagle, explains that “approximately 6-10 weeks after fledging, when they are 17-23 weeks old, the young eagles begin to break family ties and leave the nesting area. It is a time to migrate south if their natal nest is up North, or a time to go north if they are raised in the southern latitudes. In some populations that are not migratory, the young may remain in the vicinity of the nest for several years.”
-
The Decorah area is located in what is called The Driftless. The video below delivers extremely rare footage of natural phenomena and scenic beauty in the Driftless in a way never seen before. Please note that one of people involved in producing this video is a brother to RRP director John Howe, George Howe.
https://www.imdb.com/title/tt9009474/