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Eggs, Eaglets and Nesting Habits
Nesting
An eagle will return to the same nest year after year. Most nests are about four feet across and three feet deep. Each year that the eagle returns, they will restore and repair the nest. These repairs will sometimes add up to a foot a year to the width and depth of the nest. Because of this repeated restoration some of the nests become huge, weighing as much as a small car. Some nests that have become so large have toppled trees. One of these nests felled by a wind storm in Florida was collected and weighed in at 1,472
pounds!
Nests are constructed of sticks and can be 1 inch in diameter and 2 3 feet long. The top of the nest is usually flat with a depression in the middle 1 2 feet across and 4 6 inches deep. This cavity is lined with softer grasses, feathers and mosses. Eagles will continue to refurbish the nest even after the chicks have hatched. Some researchers theorize that this prevents the chicks from dangerous contact with spoiled food and parasites.
A pair of eagles may also choose to have an alternate nest site within their territory, building and refurbishing more than one nest. Only one of them will be used each season. If wind or some other disaster destroys the primary nest early in the breeding season, the eagles may lay another clutch of eggs at the alternate nest site.
Eggs
The egg of a bald eagle is a dull white with no markings except for a rare few that have pale brown spots. The eggs are about three inches in length similar to a domestic goose egg. There is no luster to the egg. The surface is rough to the touch. Typically the size of the clutch (number of eggs laid in the nest) is from 1
to 3 eggs.
These eggs are laid over a period of 2 to 4 days. A clutch that contains 3 eggs can conceivably take a week to lay, while a clutch of 2 may only take half of a week. The vast majority of nests studied have had 2 eggs laid.
If an egg is removed the eagle will not lay another to replace it. If all of the eggs are removed or destroyed for some reason the pair may likely
re-lay the whole clutch. While eagles can easily incubate more than two or three eggs, it is theorized that a large clutch produces more young than the parents can support with the environmental resources provided. In
this scenario food resources are the limiting factor for larger clutch sizes.
The farther north the eagle nests, the shorter its breeding season. For example, those birds on nests in Northern Minnesota need to wait to lay their eggs until much of the ice is gone from the lake. This can take until March or early April. This thaw allows the parent eagle to support their your with prey.
Eagles that nest near the Mississippi River, and
other open bodies of water can lay eggs as early as mid-February. Eagles that live as far south as Florida may be laying eggs in any month from early November to early February. Researchers believe that this early breeding season is timed with the arrival of northern waterfowl and may also give the chicks a better chance of developing their feathers in time to protect them from the hot summer sun.
Incubation
Eagles need to keep the growing embryos warm inside the eggs for a long time. On average, the incubation process takes 35 days.
Eagles develop an incubation patch in the area of the lower breast that loses feathers and is full of blood vessels. This allows a better transfer of heat from the adult to the egg. This incubation patch develops on both the male and the female because they share incubation duties, but only during nesting season.
Even though both of the eagles incubate the eggs, studies have shown that about 72% of the duty rests with the female and 28% is done by the male. The eggs are very rarely left unattended. There is an adult on the nest 99% of the time and the eggs are incubated for 98% of the day. If conditions are mild the eggs may be left for several minutes in the hour.
Some eagles even cover their eggs with soft nest materials before leaving them. The eggs are turned about every hour during incubation to ensure proper development of the embryos. This rotation ensures that the warmth form the parent is distributed evenly to the embryo and that the membranes dont stock to the inside of the shell.
As in most birds of prey incubation begins as soon as the egg is laid. This causes the eaglets to hatch at different times depending on when the egg was laid. This is the reason that eaglets in the same nest are different sizes.
Usually a day before the eggs hatch an adult will hear the sounds of the chick inside and bring food to the nest
to have on hand when it hatches. Adults are only able to watch while the eggs hatch. Even if the eaglet is having trouble breaking free of the shell the adult will not assist.
Eaglet Biology
Once the 35-day incubation period is over, the eaglets will puncture a hole in the egg in order to
breathe - but actual hatching will not occur until about a day
later!
It can take anywhere from 4 to 5 hours for the eaglet to break out of its shell, but may take up to two days. It usually takes violent struggles for the eaglet to break free from its shell.
The eaglet hatches with its feathers wet (from amniotic fluid) and eyes closed. Within four hours its eyes will open and the down that covers its body will become dry and fluffy.
The chick is weak at first and spends most of its time lying in the nest sleeping. At this time the parent is brooding the young or keeping them warm and protecting them from the elements. After about two weeks of age the nestling can produce enough heat
to start to stay warm on its own. After two months the juvenile plumage is enough to keep the nestling comfortable in its element.
The first downy feathers are kept for about three weeks; after that a second downy plumage replaces
the first. This secondary down plumage is long, thick and woolly, and a darker sooty
gray color. When this happens the legs also start to turn the recognizable yellow. By the seventh or eight week of life juvenile plumage has replaced the secondary down and within the next several weeks will fully develop. Juvenile eagles have a bluish black beak and dark brown eyes.
The first few weeks of life in the nest consist of fighting between nest mates. The larger of the nest mates has an advantage in getting the most food from the parent. The parent eagle will tear up prey and offer it to the first mouth it sees.
Younger chicks can succumb to parental neglect and physical and psychological abuse meted out by the older nest mate. It appears that the parent does not interfere on behalf of the weaker nestling and will feed the nestling that is the largest, most aggressive and most demanding.
When their new plumage appears they will preen (clean their feathers) regularly. After about a month they begin to grasp with their talons, peck at prey brought to the nest and cast pellets (regurgitating indigestible parts of the prey they have eaten).
After about 5 weeks they can stand on their feet and begin screaming loudly. At two months of age they will steal and monopolize food from their nest mates and exercise frequently. At nine weeks of age they may perch on branches near their nest and after about eleven weeks will fly from the nest for good. This fledging usually occurs in eagles around the Wabasha area late in June or early July.
Only about 50% of the eaglets hatched in a season will make it through their first year and fewer than that will make it to adulthood in the fifth or sixth year.
Rehabilitated Eagles
It is thought that rehabilitated birds released to the wild lead lives that are as long and are as productive as their wild kindred. Indeed rehabilitation is particularly useful for long-lived, seriously endangered species, like eagles, where adult survival can have a significant impact on present and future chick production.
Wildlife rehabilitation centers have successfully released hundreds of eagles in the past twenty years, a significant percentage of the eagles counted in the United States during that time.
If you find a sick or injured eagle please call the National Eagle
Center or follow the other instructions on our link in this website I
found an injured Raptor. Trying to capture and transport it yourself can cause great harm to you and greater harm to the already suffering bird.
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