Most immature Bald Eagles migrate, but if adults have nested in an area where water remains open year-round, they are more likely to remain in or near their breeding territories all year, defending their nest site. The risks that migrating pose are not worth it if they can get all the food they need (1/2 – 1 ½ pounds/day) to survive the winter, which they can in much of the Northeast. In the past few decades, the number of overwintering eagles has been increasing in New England to the point where it is not unusual to see adult eagles near and even at their nests any month of the year. (The accompanying photo taken in Vermont on 11-14-20.)
Eagles do make changes in order to adapt to winter conditions. While they continue to feed on fish, they also do a fair amount of scavenging in the winter, feeding on roadkills and animals such as deer that may have wandered onto the ice, fallen and not been able to get back up.
Another behavioral change that occurs is the tendency to gather in large numbers, clustering close together on branches at overnight roost sites. Often stands of white pine provide the birds with some protection from the cold wind, thus allowing them to conserve energy. An additional advantage of this communal life style is that they get cues from each other as to where sources of food may be by watching the direction in which the first birds take flight in the morning (those with a known source of food often are the first to leave the roost).
Congratulations to Jill Osgood (“osgoodjill”), the first reader to correctly identify the pellet of either a Bald Eagle or an Osprey. Many people are familiar with bird pellets – lumps of material consisting of the indigestible parts of a bird’s diet which are regurgitated by the bird hours after they’ve eaten their prey. Raptors often consume their prey whole, including parts that are not easily digestible such as fur, feathers, bones, teeth, nails, etc. These parts get as far as the proventriculus, an organ located between the esophagus and the gizzard, where they are packed into a pellet.
We often associate pellets with owls, but many species of birds, in addition to owls and other birds of prey, form pellets. They include grebes, herons, cormorants, gulls, terns, kingfishers, crows, jays, dippers, shrikes, swallows, and most shorebirds. The size of the Mystery Photo pellet (3” long) indicates that the bird that regurgitated it was very large – in general, the larger the bird, the larger the pellet. It was found near the shore of Lake Champlain, where Ospreys and Bald Eagles are not uncommon.
If I had to, I would guess the pellet was regurgitated by a Bald Eagle. Osprey are piscivores, eating primarily fish, and bald eagles are carnivores, eating a variety of fish, mammals and amphibians. A close look at the pellet reveals, in addition to fur and fish scales, the upper mandible of a very small rodent on the left hand end of the pellet. An Osprey’s pellets consist of primarily scales and bones, whereas a Bald Eagle’s pellets are composed primarily of hair (its stomach acid breaks down the bones and scales).
Twelve to eighteen hours after consuming prey, a Bald Eagle casts a pellet. Relatively odorless and light-weight, these pelleted remains can reveal the varied diet of this raptor.
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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The 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)
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.
Eagles 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.
For 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.)
For 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.
When 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)
In the Northeast, Bald Eagles seek out the tallest trees around in which to build their nests. In certain locations in Alaska, coastal California and northern Canada where there are no trees, Bald Eagles will nest on the ground. When building a nest in a tree, eagles will usually build it in the top quarter of the tree, just below the crown, on limbs capable of supporting a large nest. Sticks from the ground are collected up to a mile away from the nest or are broken off of nearby trees. Additional materials are regularly added to the nest throughout the year, including daily additions during the breeding season (see photo).
Many live eagle cams can be found online (in Minnesota, one chick, one egg – http://mnbound.com/live-eagle-cam/ ; in Georgia, older nestlings: http://www.berry.edu/eaglecam/ ; in Pennsylvania, very young chicks: http://www.ustream.tv/decoraheagles ), giving the viewer a window into the incubation, birth and growth of these raptors. Depending on the location of the nest, one can see every stage of development, from eggs to hatchlings to all-but-fledged nestlings. In New England, eggs are soon to hatch, if they haven’t already. (Thanks to Marianne Blake for photo op.)
Bald Eagles in New England are repairing and adding to their nests, even as snow and cold temperatures continue. They often reuse their nest year after year – a nest in Ohio was used 34 years before the tree blew down. Although most don’t reach the record-breaking dimensions an eagle nest in Florida did (9 1/2’ wide, 20’ deep, weighing almost 3 tons), they are impressive structures, averaging five feet and three feet deep. Typically eagles will choose one of the biggest trees in an area in which to build their nest. Because their nests will be used for many years to come, eagles often choose living trees (which will remain standing longer) in which to build them. The nest is usually located in the top quarter of a tree, just below the crown. Both male and female eagles collect sticks for the nest, either finding them on the ground or breaking them off nearby trees. In parts of Alaska and northern Canada where trees are scarce and short, eagles often nest on the ground.
Biologists estimate that there were up to 500,000 Bald Eagles (Haliaeetus leucocephalus) in North America when the first European settlers began arriving. Seventy-five years ago you wouldn’t have seen a single Bald Eagle in the state of Vermont. Thanks to the banning of DDT in North America, an effective reintroduction program in Vermont between 2004 and 2006, and the protection of Bald Eagle breeding and wintering habitat through the Endangered Species Act, Vermont now has a healthy breeding population of eagles. This summer 16 Bald Eagles nested in Vermont and 26 young eagles fledged. Winter records of Bald Eagles reflect this increase as well – 24 eagles (13 of which were immature birds) were found in the 2013 annual Midwinter Bald Eagle Survey in Vermont, with the largest numbers occuring near open water, such as Lake Champlain and the Connecticut River, where the eagles have access to fish. (You can also find them at frozen lakes where there generous ice fishermen.) Eagles are still listed as endangered in Vermont, but they are off the national Endangered Species list, and biologists say they should soon be off the state endangered list as well.
Raucous crow and raven calls alerted me to the fact that something, most likely a bird of prey, was in the area (crows and ravens often mob and harass hawks and owls). Through the trees I got a glimpse of a raven flying beside another bird that dwarfed the raven. Soon there were two of these large birds, dipping and diving in the wind, seemingly enjoying themselves no end. They turned out to be juvenile bald eagles, last year’s young. Perhaps they were practicing for the acrobatic courtship flight displays they’ll be performing in three or four years.