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Mating happens by pressing cloaca together – This is also known as the ‘cloacal kiss’. The female will lean forward, the male will land on her back. The female will move her tail feathers to one side, the male will press and twist his cloacal opening around her cloaca, passing the sperm from his cloaca to hers.

Generally, eagles may mate throughout the year depending on if the pair migrates. Frequent mating strengthens their bond to each other and increases the chance of fertile eggs, the female may have 3 two week windows throughout a breeding season where she is fertile. The male’s sperm is said to be viable inside the female for 10 days. Increasing daylight hours causes the females pituitary gland to secrete a hormone that turns on the ova. The ova is turned off by prolactin which is the hormone associated with incubation. 

Double clutching is laying a second set of eggs. This typically happens after the first set is removed (this was done during early Bald Eagle reproduction days to increase the amount hatched each year. The first clutch was usually artificially incubated). In the wild, a double clutch could happen if the eggs were damaged by being stepped on or lost to other animals.

Eagle biologist, Dr. Peter Sharpe, states: “Eagles will generally not lay another clutch if they have incubated for more than about 2 weeks, so there is probably a switch that is triggered by a particular amount of incubating that does not allow them to become fertile again within a season.”

Bald Eagles tend to soar alone, rather than flocking with other eagles. However, they sometimes concentrate in the same place due to a plentiful common food source, or for shelter from the cold wind. – BH

Yes. They select a breeding territory based upon an evaluation of all the things they are looking for: food supply, suitable nesting and perching trees, and isolation from excessive human activity.

These areas are usually near where they themselves fledged as youngsters.

Wintering birds do not establish a territory, but usually do use the same area each winter. – PN

Absolutely. They are very good swimmers. Even nestlings that haven’t learned to fly can swim! It’s not uncommon for an eagle to “misjudge” and latch into a fish too heavy / large for it to fly with, so they then may swim quite a distance to shore, and eat the fish there. – PN

This varies, and there is not one answer to this. It is very dependent on the time of year, the availability of prey, weather conditions, age of the eagle, and many more things.

Obviously, during migration, for those eagles that do migrate long distances each spring and fall, average daily flights can be 124 miles or more.

While on the wintering and breeding grounds, flights are much shorter, and depend heavily on prey availability, suitable roosting locations, and weather.

During non-migratory times, probably less than 10 – 20 miles per day (or less).

Regarding differences between males and females: the distance would be approximately the same during migration, but in breeding situations, the males will travel farther and do more of the food provisioning, while the females will stay closer to the nest, even when they are relieved by the male at the nest. – PN

• They typically build their nests high up in a tree, almost always with commanding views of their surroundings (all the better to avoid and see their enemies)
• They typically build their nests near water (all the easier to spot and access food)
• They vigorously defend their nesting territory when breeding, yet become gregarious when not breeding.
• They are sensitive to and avoid disturbance
• They will build and use alternate nests
• They will sit (perch) for long hours; in winter, for up to 98 percent of the day, conserving energy.
• They will select winter night roosts that meet very specific criteria (slope, aspect, etc.)
• They will eat carrion.

Here are some traits, but not instincts:

• Their eyesight
• Their specially adapted legs, feet, and talons
• Their distinct plumage, especially that of young birds (mostly brown and cryptic)
  Their size
• Their delayed sexual maturity and long life span
  The larger size of fledglings –     – PN

A good general rule seems to be that eagles can carry up to half of their own weight. This obviously means female eagles are able to carry more larger prey than the males.

Depending on the size of a Bald Eagle, it can lift between 4 – 6 kilograms (8.8 – 13 lbs). Some Alaskan eagles have been recorded lifting weights of well over 7 kg (15.4 lbs).  Sometimes eagles have trouble judging the weight of prey. Eagles in Alaska have “locked on” to a large salmon, obviously heavier than could be carried away in flight, and the eagle then floats and swims to shore with its prey rather than give up the prey. – PN

With wildlife, it is often hard to determine reasons behind behaviors we may observe. Talon-grappling and tumbling are frequently observed behaviors; seen between all combinations of eagles—between mated adults, un-paired adults, adult and immatures, immatures with immatures, etc. These are also likely “unions’ of any-sex combination of birds.

That variety of participants, tells me right away there is no one answer to what this behavior is for, but rather, that it happens for a variety of reasons.

Three come to my mind immediately: pair-bonding, aggression, and play. We also know from observation that these represent very aggressive encounters, where sometimes, one or both of the participants are killed (sometimes they cannot “un-lock” and crash to the ground together. The most often I see this, is with and between immatures, and I’m convinced it is both play and learning (flight capability). I do believe that eagles get enjoyment out of certain activities, which could be called play, such as when they chase each other in flight, tumble, roll, etc. As with humans, I think immature Bald Eagles are more prone to “play” than adult birds. – PN

Bald Eagles have several distinct vocal sounds. The ‘Peal Call’ consists of high-pitched, prolonged, gull-like cries. The ‘Chatter Call’ consists of 3 – 4 introductory notes separated by short gasps of silence and then followed by a rapid sequence of descending notes. They also make a low ‘kuk-kuk-kuk’ call. Females tend to have lower pitched calls than males. Juvenile Eagles have their own ‘Peal Call’ as well as a chirping sound they use as nestlings to beg for food.

A bird’s eggshell has thousands of tiny pores, which allow water and gas to pass through. Mammals like us get oxygen through an umbilicus, but developing birds receive oxygen and remove carbon dioxide through the egg shell. Gases, including oxygen, enter and leave the egg by diffusing through the pores in its shell, across the outer and inner shell membranes, and into the blood in the capillaries of a special tissue called the CAM, or chorioallantoic membrane. Condensation can form on eggshells if exposed to excessive humidity, which clogs shell pores and provides a vehicle for bacteria. The result? Fatal suffocation and/or contamination. Only the eagles know for sure, but I think they may have responded to the threat of rising humidity levels by leaving their eggs uncovered. Standing or leaving entirely allows fresh air to circulate over the eggs, dropping the humidity level and giving the developing embryos fresh air.”

After approximately 35 days, the eaglet inside the egg is ready to hatch. An “egg tooth” has been formed at the top of its beak to assist in this process.  In addition, a very strong muscle on the back of its neck has developed, which assists with the work of punching through the membrane inside the egg.

Inside the egg, at the top, is an air bubble, and breaking the membrane inside the egg allows the eaglet to breath its first breath of air inside the egg shell. This little bit of air will give the eaglet energy to continue to break free of the shell.  During this time, the  yolk of the egg is absorbed into the stomach of the eaglet, providing more energy.

Using its egg tooth, the eaglet scratches around the inside of the shell to weaken it. Finally, a tiny hole or crack emerges. This is called a “pip.” Breaking free from the egg is an extremely tiring process for the eaglet, and can take up to 2 days from the first pip to an actual hatch.  During the process, the eaglet sometimes will rest for awhile. During the hatching process, the eaglet slowly rotates counterclockwise by pivoting its legs, all the while scratching the inside of the shell with its egg tooth.

 A hatch is complete when the eaglet is totally out of the shell.

The parent eagles do not assist in the process, but they seem to be aware when the eaglet is ready to hatch.  They can even hear the tiny peeps coming from inside the shell, and will occasionally move off the eggs they are incubating and look down to see what is happening.

Eaglets come into the world totally helpless.  They cannot hold their head up; their vision is limited; their legs are too weak to hold their weight. Bald eagles are altricial, which means they must rely 100 percent on their parents to protect them and care for them.

It can take days for them to completely hatch from the first pip to being totally free from the shell (in the nest of Romeo & Juliet in Florida, the first eaglet hatched (NE16) in 2016 took 40 hours to complete the process. Often, it’s much quicker than this.

After hatching, the eaglet will dry off and fluff up to a downy gray.  Food will be offered to the eaglet by the parent, who shreds meat off fish or whatever is available.  Tiny pieces will be offered again and again as the eaglet struggles to hold his wobbly head still long enough to take the food.  In a short time, the eaglet becomes stronger and his eating skills and coordination develop quickly.

An eaglet has a crop – a storage area – below its chin. Food goes into the crop and is then digested as needed.  When the crop is “full” you can see it bulging out.  The crop is actually part of the esophagus where food is stored and softened. The crop regulates the flow of food through the digestive tract.

• The eaglets grow rapidly, they add about a half pound to a pound of body weight every week until they are about 9-10 weeks old, depending on if the eaglet is a male or female. Females are always larger.
• At about two weeks, it is possible for them to hold their head up for feeding. At this age, the eaglets can also thermoregulate. Thermoregulation means that the eaglets now have the ability to maintain a near constant body temperature. They don’t have this ability at birth, so the parent eagles must brood them consistently until the eaglets reach this important milestone.
• At about three weeks they are 1 foot high and their feet and beaks are very nearly adult size.
• At about three to four weeks old the eaglets are covered in a secondary coat of gray down.
• At about four to six weeks, the birds are able to stand, at which time they can began tearing up their own food.
• At about three to six weeks, black juvenile feathers will begin to grow in. While downy feathers are excellent insulators, they are useless and must be replaced with juvenile feathers before an eaglet can take its first flight, some 10 to 14 weeks after hatching.
• At about six weeks, the eaglets are very nearly as large as their parents.
• At about eight weeks, the appetites of the eaglets is at its greatest. The parents will hunt almost continuous to feed them, meanwhile at the nest the eaglets are beginning to stretch their wings in response to gusts of wind and they may even hover for short periods. The eaglets grow stronger.
• At about nine to ten weeks, they begin branching, this is a precursor to fledging.
• Around ten to fourteen weeks, the eaglets will fledge, or fly away from, the nest.
• Once the eaglets have fledged they may remain around the nest for four or five weeks, taking short flights while their primary feathers grow and strengthen. Their parents will still provide all of their food. The juvenile fledglings, with the exception of their color, look similar to their parents, but are nothing like them in behavior. The juveniles now have to learn to hunt, and they only what’s left of summer to learn. After that, they’re on their own. The first winter is the most dangerous and difficult part of an eagle’s life.

All eagles are renowned for their excellent eyesight, and the Bald Eagle is no exception. They have two foveae, or centers of focus, that allow the birds to see both forward and to the side at the same time. 

Bald Eagles are capable of seeing fish in the water from several hundred feet above, while soaring, gliding, or in flapping flight. This is quite an extraordinary feat, since most fish are counter-shaded, meaning they are darker on top and thus harder to see from above. 

Eagles have eyelids that close during sleep. For blinking, they also have an inner eyelid called a nictitating membrane. Every three or four seconds, the nictitating membrane slides across the eye from front to back, wiping dirt and dust from the cornea. Because the membrane is translucent, the eagle can see even while it is over the eye.

Eagles, like all birds, have color vision. We believe they can see in color based upon the more numerous “cones” in their retina. Cones are known to be necessary for acuity and color visions, versus the “rods” which are for sight in low-light conditions, something eagles are not especially adapted to.

 An eagle’s eye is almost as large as a human’s but its sharpness is at least four times that of a person with perfect vision. The eagle can probably identify a rabbit moving almost a mile away. That means that an eagle flying at an altitude of 1000 feet over open country could spot prey over an area of almost 3 square miles from a fixed position.

 A Bald Eagle’s eye changes color as it reaches maturity. Nestling eagles’ eyes are nearly black. Juvenile eagles (first year birds just out of the nest), have brown eyes (which can vary in how light or dark they are, but usually they are pretty dark). As they become immature eagles (ages 2, 3), their eye lightens to a light brown.

The feet are featherless (scaled). They have 4 toes, each with a very serious claw (talon). Three toes face forward; the 4th (the hallux) is longer and faces backward to aid in gripping prey. These hallux talons are almost 2 inches long on large female eagles, and only about an inch and a quarter on small males.  Talons are made from the same material as human fingernails, and are very similar to a dog’s nails. The real strength of talons comes from the muscles in the legs. When they contract, they clamp the tendons in the lower legs and does down, closing all the talons together in a vice-like grip.    – PN

Birds in general have a higher metabolic rate than humans, which demands that they process their food as quickly as possible. This means getting it into a form from which they can extract the energy they need, quickly and efficiently.

Birds, including eagles, have adaptations for doing this. Most importantly, part of their stomach has turned into a gizzard, in which food is ground down to a fine consistency to permit rapid digestion. In eagles, this is also the place where pellets are formed. These are masses of material from prey that cannot be digested, such as fur, feathers, and occasionally bone, that then travel backwards from the gizzard up to the mouth and are cast (like vomited) out the mouth. Depending on what they have eaten, pellets are formed after the meal, overnight, and are usually cast out the next morning.

Most fish are digested completely. Eagles have very strong stomach acids, and can digest bone quite well, which aids them in their own bone formation and in their egg-shell formation.

Another major feature in their digestive system is that eagles (and other birds) have something called a crop, in the upper alimentary track (esophagus) where food can be stored for days. This is extremely beneficial to eagles, who can store up to two pounds of food in their crop when prey is abundant, so they can then go without food for several days if need be. – PN