Bald Eagles Give & Take
Although a Bald Eagle is massive, has excellent eye sight, powerful leg muscles and strong talons to grip prey with, their predilection for foraging for live prey (mostly fish but also mammals, birds and reptiles) isn’t as great as one might imagine. Often they (particularly immature eagles who lack experience foraging) resort to scavenging dead animals or stealing prey from other birds rather than capturing live prey. Marauded birds include ospreys and herons which are better at capturing live fish and aren’t particularly good at defending themselves.
What seems fitting given that eagles secure much of their food from other birds is that they in turn provide many birds and predators with a meal . Crows, ravens, coyotes, bobcats, and foxes all are known to move in when they become aware of an easy dinner. Eagles are said to be easily displaced by these species at scavenging sites. The pictured American Crows, however, are patiently waiting their turn. (Photo: American Crows waiting for 2nd year Bald Eagle to finish feeding on a fish; inset – Bald Eagle’s 5″-long tracks)
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Happy Valentine’s Day !
May you enjoy the warmth of friendship today and every day!
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Fish are a primary, but not exclusive, food source for Bald Eagles
Hands down, Bald Eagles (like the 2nd year immature bird pictured) prefer fish over other prey — roughly 56% of the diet of nesting Bald Eagles consists of fish such as salmon, herring, shad, and catfish. However, eagles are opportunistic foragers and over 400 species of prey have been recorded, half of which are waterbirds. Reptiles, amphibians, invertebrates such as crabs and crayfish, and small mammals such as squirrels, rabbits, muskrats, young beavers, fawns and raccoons are also subject to Bald Eagle predation.
During their first year, until they learn to be proficient hunters, Bald Eagles frequently feed on carrion. Even as adults, eagles regularly consume roadkills and deer that have died as a result of being stranded on ice. Whatever food is available and requires the least amount of energy to capture is usually high on their list.
Although not considered a primary source of food, domestic pets are subject to occasional predation by eagles. A discovery made by Fish & Wildlife personnel engaged in banding Bald Eagle nestlings may be of interest to cat owners who allow their pets to roam free in the great outdoors. Upon reaching one nest, they found, among the detritus, over 20 cat collars.
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Bald Eagles Year-Round Residents In Much Of The Northeast
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).
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Mystery Photo: Bald Eagle or Osprey Pellet
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.
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Common Loon Chicks Riding High
July on a lake occupied by nesting Common Loons is a birder’s slice of heaven. Eggs are hatching, day-old fluff balls are riding high on their parents’ backs, parents are busy catching and delivering small fish and crayfish to their chicks, and survival lessons are being given. Recently while watching a pair of two- or three-day-old chicks whose parents were off obtaining their offspring’s next meal I observed a juvenile Bald Eagle, known predator of Common Loon chicks, soaring overhead. Within a split second both loon chicks dove and stayed submerged long enough for the eagle to give up the ghost. Nature or nurture?
To see a related entertaining phenomenon, go to https://loonproject.org/2019/06/29/unlikely-allies/?fbclid=IwAR0po44dJaElcyYpqKqLwaz9A6gs7RxWfhJRkoB-QleC7sUGnjgElksR5G4.
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Common Loon Chicks Hatching
Newly-hatched Common Loon chicks can swim as soon as they hit the water, which they do as soon as their down dries after hatching, usually within 24 hours. Their buoyancy and lack of maneuverability, however, leave them vulnerable to predators. Parents usually don’t stray far from their young chicks due to the omnipresent threat of eagles, hawks, gulls, large fish and snapping turtles. During their first two weeks, young loon chicks often seek shelter (and rest) on the backs of their parents.
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Bald Eagles On Eggs
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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Common Loon Chicks Riding High
Why do Common Loon chicks ride on their parents’ backs for the first two weeks of their life? There are several reasons. Loon chicks leave their nest as soon as their downy feathers are dry; if they stayed in their ground nest, they would be very vulnerable to predators on land. For the same reason, they rarely return to their nest.
Like many young birds, loon chicks can’t immediately regulate their body heat. Many birds brood their young in the nest, providing them with warmth and shelter. Common Loon parents brood their young on their back (and under their wings). On windy, cloudy, cool days, the chicks are nowhere to be seen, huddled under their parents’ wings. On calm, sunny days, they are in full view.
Although they can swim immediately after hatching, loon chicks are very buoyant and have difficulty maneuvering. Predators such as Bald Eagles, Common Ravens and gulls are quick to prey on young loons that have no parental protection. In addition, predatory fish such as Northern Pike and Largemouth Bass are a threat. Once they are several weeks old, the chicks are not only bigger, but they are more mobile and can avoid predators more easily.
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Bald Eagle Eyesight
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)
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Sea Lampreys Spawning In Connecticut River
Sea Lampreys aren’t a common sight, but an opportunity presented itself after this Bald Eagle “rowed” from the middle of the Connecticut River to the shore with its too-heavy-to-lift prey, ate a portion of it and flew to its nest with a slightly lighter load. At first glance I thought it had captured a large snake, but closer inspection revealed that a three-to-five pound Sea Lamprey approaching 30 inches in length was clasped in the eagle’s talons!
Lampreys were accidentally introduced into the Great Lakes and Vermont’s Lake Champlain, where they became parasites of other fish due to being landlocked. However, during the time the native Sea Lampreys are found in the Connecticut River, they are not parasitic. These fish are anadromous – they live as adults in the ocean (where they are parasitic) and return in May and June to spawn in fresh water.
Sea lamprey young spend three or four years as worm-like creatures burrowed in the soft mud of the Connecticut River. When they reach five or six inches (which can take up to ten years), young lamprey head for the sea. The ocean-dwelling adults uses their round, rasping mouth – filled with concentric circles of teeth – to scrape a hole in the side of a host fish and feed on blood and body fluids before letting go. They weaken, but don’t kill, their hosts. After spending one to two years in salt water, Sea Lamprey head back to the closest freshwater stream or river, migrate upstream, cease feeding and spawn. They never return to the ocean, as they die after mating and laying eggs.
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Bald Eagles Tending Young Eaglets
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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Bald Eagles Turning Eggs
Bald eagles are on their nests, incubating their one-to-three eggs. Although there isn’t much activity at this point, what activity there is, is extremely important to the survival of the embryos inside the eggs. Maintaining the temperature of the eggs is crucial. Bald eagles must incubate their eggs for 35 days. During this time, the eggs must remain at a steady temperature of 99.5 degrees Fahrenheit. If the incubating parent is frightened away from the nest or leaves the nest even very briefly, the egg may become too cold or too hot, depending on the weather.
During the entire incubation period, the eagle parents continuously turn the eggs with their feet and beak. The main function of this action is to prevent the embryos from sticking to the inside of the egg shell. In the early days of incubation, it’s important that the embryo floats inside the egg while the membranes that support its life are growing and developing. Turning optimizes membrane growth. Eventually the membranes will be pressed to each other and to the shell. If these membranes adhere too soon the chick will not be able to move into the hatching position later and get out of the egg. To see a nesting bald eagle turning eggs, go to http://www.eagles.org/dceaglecam/.
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Carrion a Vital Food Source for Bald Eagles
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.
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Juvenile Bald Eagles Fledging
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.)
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Young Eagles Preparing to Fledge
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.
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Eaglets Hatching
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)
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Bald Eagles Nesting
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.)
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Great Horned Owls Incubating Eggs
Great Horned Owls are said to have the widest range of nest sites of any bird in North or South America. Like other owls and falcons, this raptor does not build its own nest, but rather relies heavily on abandoned stick nests of diurnal birds of prey. Red-tailed Hawk nests are often usurped, as well as those of Bald Eagles, crows, ravens and herons. Nests may be lined with shreds of bark, leaves, downy feathers from the owl’s breast, fur of prey and trampled pellets. In addition to bird nests, Great Horned Owls also raise their one to four nestlings (usually two) in tree cavities and snags, on cliffs, in deserted buildings, in squirrel nests and even on the ground.
The female Great Horned Owl does all the incubating; the male delivers prey to her at intervals throughout the night. These early nesters have incubated eggs successfully when outside temperatures have been as low as -27°F. Hopefully warmer temperatures will welcome the newly hatched owlets in about a month. (photo: mostly hidden Great Horned Owl in Great Blue Heron nest)
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Bald Eagles Refurbishing Nests
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.
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Bald Eagles Year Round in Vermont
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.
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