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Posts tagged “Haliaeetus leucocephalus

Bald Eagles On Eggs

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Thanks in large part to the Vermont Bald Eagle Restoration Initiative, seeing eagles in Vermont is not all that unusual these days, even in winter. The open water of Lake Champlain (as well as ice fishermen and White-tailed Deer carcasses in other parts of the state) allow them to survive here during our coldest months. Vermont’s mid-winter Bald Eagle Survey documented 84 eagles in January, 2018.

Equally as encouraging is the growing breeding population of eagles in this state. This past year 21 adult Bald Eagle pairs successfully produced 35 young in Vermont. The return of eagles to their nest site is always a much- anticipated event, which often coincides with the opening up of the Connecticut River for at least one pair that nests on its banks (see photo).

Eggs have been laid and eagles (both male and female) are engaged in incubating them for the next month.  One can’t help but be impressed by their perseverance — recently they endured three Nor’easters in 10 days while incubating their eggs (note snow on rim of nest)!

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Bald Eagle Eyesight

7-26-16  juv. bald eagle2 026The eyesight of a Bald Eagle is impressive.  Part of the reason for their excellent vision is that these birds of prey have two centers of focus (foveae), which allow them to see both forward and to the side at the same time. Cone cells, one of three types of photoreceptor cells in the retina, perceive color, fine detail and rapid movement.  In a human, the fovea has 200,000 cones per millimeter; in the central fovea of a Bald Eagle’s eye, there are about a million cones per millimeter. 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.

Bald eagles are capable of seeing fish in the water from several hundred feet above, while soaring, gliding or in flapping flight.  (They locate and catch dead fish much more rapidly and efficiently than live fish, because dead fish float with their light underside up, making them easier to see.)  It is very likely that a Bald Eagle can identify a rabbit moving almost a mile away. This would mean 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. (photo: recently fledged, juvenile Bald Eagle)

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Bald Eagles Tending Young Eaglets

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In the Northeast, Bald Eagle eggs are hatching and the heads of the one-to-three chicks can be seen bobbing up and down, anxiously begging for a tidbit of food from one of their parents.  For the first two or three weeks, their mother stays with them 90 percent of the time, keeping them warm and tearing food brought by their father into little pieces that she feeds to her chicks.  Eventually food-gathering is shared equally between the parents, and is usually sufficient to produce a weight gain of 3 ½  ounces a day for male chicks, and 4 ½ ounces per day for the female chicks. (Female raptors are typically larger than the males.)  The chicks in these photos are approximately two weeks old and are covered with their darker, second coat of down, which comes in when they are a little over a week old.

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Carrion a Vital Food Source for Bald Eagles

3-1-16 eagle3 036Eagles obtain food mainly in three ways — by direct capture, scavenging for carrion and stealing food from other birds and mammals. When securing their own live prey, they hunt from perches or soar over suitable habitat, taking most prey on the wing. Bald eagles’ preferred food is live fish, but they are opportunistic foragers that select prey based on availability. Twenty studies from across their range found that the composition of bald eagle diets averaged the following: fish-56%; birds-28%; mammals-14%; and other 2%.

In addition to capturing live prey, eagles rely heavily on fish, bird and mammal carrion, especially during the winter. Ice fishermen’s leftover bait and/or rejected catches, roadkills and deer that have slipped and died on ice-covered ponds and lakes are three heavily-used sources of food at this time of year. If the carrion is small enough, it is often carried to a perch (see opossum in photo) where it is inconspicuously consumed. Larger carrion, such as white-tailed deer, salmon and waterfowl, that are too big to carry off, are eaten on site and repeatedly visited until consumed.

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Juvenile Bald Eagles Fledging

7-17-15 juvenile eagle 003For several weeks before leaving their nest, young bald eagles constantly flap their wings, occasionally lifting themselves off the nest several inches in mid-air. Eventually they succeed in making short “flights” to nearby branches and then back to their nest. The young eagles are strengthening their wing muscles, practicing landing, and beginning to master flight.

Sometime between 8 and 14 weeks juvenile bald eagles leave their nest. Many fledge successfully, but up to half of the nest departures are unsuccessful, with the young ending up on the ground where they may stay for weeks before flight is achieved. During this time the parents usually continue to feed their young, but the juvenile eagles are far more vulnerable to predators. If the flightless, grounded juveniles are approached or threatened, or if they simply want to move from one spot to another, they walk or run on the ground (see photo).

The young bald eagle pictured was blown out of its nest prematurely and landed on the ground. Eventually it managed to fly back up onto a branch in the nest tree. The parents continued to feed the eagle while it was on the ground, as well as after it was back up in the tree. (Thanks to Linda and Roger Whitcomb for photo op.)

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Young Eagles Preparing to Fledge

6-11-15 eaglet 062For several weeks prior to their first flight from their nest, Bald Eagle nestlings practice flapping their wings to the point of lifting themselves up several inches into the air. This develops their wing muscles, flight coordination and landing ability.

At anywhere from eight to fourteen weeks of age, juvenile Bald Eagles fledge, or leave their nest. According to Birds of North American Online, up to half of young Bald Eagle nest departures are unsuccessful. The young land on the ground and may remain there for weeks before regaining flight ability. More often than not their parents will continue to feed them, but they are much more vulnerable to predation in this situation. Fledglings may continue to use their nest as a feeding platform for several weeks after leaving it, as they gain flight and foraging skills.

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Eaglets Hatching

bald eagles2  254When eagle chicks hatch they are covered with light gray down and have brown eyes and pink legs. One parent, usually the female, spends most of the day in the nest with her young for the first three weeks, brooding and keeping them warm. The male provides most of the food during this time. After he delivers prey, she tears off small pieces and feeds them to the nestlings. The chicks gain weight rapidly – roughly ¼ pound a day – so that in three or four short weeks the young are nearly the size of an adult. Eaglets are roughly six weeks old before they are capable of tearing off food and feeding themselves, and at least eight weeks old before they leave the nest. (Note corn stalk that’s been incorporated into nest; photo: one-week-old eaglet & its mother)

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