Learn About Bald Eagles

In this episode of the I Can't Sleep Podcast, fall asleep learning about bald eagles. These regal and majestic birds look beautiful perched on a tree or soaring in the sky, but learning all the things I did about these birds taught me one thing: this stuff is just not that interesting.

Happy sleeping!

Transcript

Welcome to the I Can't Sleep Podcast, Where I read random articles from across the web to bore you to sleep with my soothing voice. I'm your host, Benjamin Moster. Today's episode is from a Wikipedia article titled, Bald Eagle. The bald eagle is a bird of prey found in North America. A sea eagle, It has two known subspecies and forms a species pair with the white-tailed eagle, Which occupies the same niche as the bald eagle in the Palaearctic. Its range includes most of Canada and Alaska, All of the contiguous United States and northern Mexico. It is found near large bodies of open water, With an abundant food supply and old-growth trees for nesting. The bald eagle is an opportunistic feeder which subsists mainly on fish, Which it swoops down upon and snatches from the water with its talons. It builds the largest nest of any North American bird, And the largest tree nests ever recorded for an animal species, Up to 4 meters deep, 2. 5 meters wide, And 1 metric ton in weight. Natural maturity is attained at the age of 4 to 5 years. Bald eagles are not bald, The name derives from an older meaning of the word, White-headed. The adult is mainly brown with a white head and tail. The sexes are identical in plumage, But females are about 25% larger than males. The yellow beak is large and hooked, The plumage of the immature is brown. The bald eagle is the national bird of the United States of America and appears on its seal. In the late 20th century, It was on the brink of extirpation in the contiguous United States. Populations have since recovered, And the species' status was upgraded from endangered to threatened in 1995, And removed from the list altogether in 2007. The bald eagle is placed in the genus Haleatus, Sea eagles, And gets both its common and specific scientific names from the distinctive appearance of the adult's head. Bald in the English language is from an older usage, Meaning, Having white on the face or head, Rather than hairless, Referring to the white head feathers contrasting with the darker body. The genus name is Neolatin, Haleatus, From the ancient Greek haleitos, Literally, Sea eagle, And the specific name Leucocephalus, Is Latinized, Ancient Greek, Leuskos, White, And kephali, Head. The bald eagle was one of the many species originally described by Carl Linnaeus in his 18th century work, Systema Naturae, Under the name Valkoleucocephalus. There are two recognized subspecies of bald eagle. H. I. Leucocephalus is the nominate subspecies. It is found in the southern United States and Baja California Peninsula. H. I. Washingtonesis, Synonym H. I. Alaskanus townsend, 1897, The northern subspecies, Is larger than the southern nominate, Leucocephalus. It is found in the northern United States, Canada, And Alaska. The bald eagle forms a species pair with the white-tailed eagle of Eurasia. This species pair consists of a white-headed and a tan-headed species of roughly equal size. The white-tailed eagle also has overall somewhat paler brown body plumage. The two species fill the same ecological niche in their respective ranges. The pair diverged from other sea eagles at the beginning of the early Miocene, At the latest, But possibly as early as the early Middle Oligocene, 28 million years ago BP, If the most ancient fossil record is correctly assigned to this genus. The plumage of an adult bald eagle is evenly dark brown with a white head and tail. The tail is moderately long and slightly wedge-shaped. Males and females are identical in plumage coloration, But sexual dimorphism is evident in the species, In that females are 25% larger than males. The beak, Feet, And irises are bright yellow. The legs are feather-free and the toes are short and powerful with large talons. The highly developed talon of the hind toe is used to pierce the vital areas of prey, While it is held immobile by the front toes. The beak is large and hooked with a yellow sear. The adult bald eagle is unmistakable in its native range. The closely related African fish eagle, Holleatus vocifer, From far outside the bald eagle's range, Also has a brown body, Albeit of somewhat more rufous hue, White head and tail, But differs from the bald eagle in having a white chest and black tip to the bill. The plumage of an immature is a dark brown overlaid with messy white streaking until the 5th, Rarely 4th, Very rarely 3rd year, When it reaches sexual maturity. Immature bald eagles are distinguishable from the golden eagle, The only other very large non-vulturine raptorial bird in North America, In that the former has a larger, More protruding head with a larger beak, Straighter edged wings, Which are held flat, Not slightly raised, And with a stiffer wing bead and feathers which do not completely cover the legs. When seen well, The golden eagle is distinctive in plumage with a more solid warm brown color than an immature bald eagle, With a reddish-golden patch to its nape, And, In immature birds, A highly contrasting set of white squares on the wing. The bald eagle has sometimes been considered the largest true raptor exopytrid in North America. The only larger species of raptor-like bird is the California condor, A New World vulture which today is not generally considered a taxonomic ally of true exopytrids. However, The golden eagle, Averaging 4. 18 kg and 63 cm in wing cord length in its American race, Is merely 455 g lighter in mean body mass, And exceeds the bald eagle in mean wing cord length by around 3 cm. Additionally, The bald eagle's close cousins, The relatively longer-winged but shorter-tailed white-tailed eagle and the overall larger Steller's sea eagle, May rarely wander to coastal Alaska from Asia. The bald eagle has a body length of 70-102 cm. Typical wingspan is between 1. 8 and 2. 3 m, And mass is normally between 3 and 6. 3 kg. Females are about 25% larger than males, Averaging as much as 5. 6 kg, And against the male's average weight of 4. 1 kg. The size of the bird varies by location and generally corresponds with Bergman's rule. The species increases in size further away from the equator and the tropics. For example, Eagles from South Carolina average 3. 27 kg in mass and 1. 88 m in wingspan, Smaller than their northern counterparts. One field guide in Florida listed similarly small sizes for bald eagles there, At about 4. 13 kg. Of intermediate size, 117 migrant bald eagles in Glacier National Park were found to average 4. 22 kg, But this was mostly, Possibly post-dispersal, Juvenile eagles, With 6 adults here averaging 4. 3 kg. Between eagles in Arizona, Winter weights are usually the highest of the year since, Like many raptors, They spend the highest percentage of time foraging during winter, Were found to average 4. 74 kg. The largest eagles are from Alaska, Where large females may weigh more than 7 kg and span 2. 44 m across the wings. A survey of adult weights in Alaska showed that females there weighed on average 5. 3 kg, Respectively, And males weighed 4. 23 kg, Against immatures which averaged 5. 09 kg and 4. 05 kg in the two sexes. An Alaskan adult female eagle that was considered outsized weighed some 7. 4 kg. R. S. Palmer listed a record from 1876 in Wyoming County, New York, Of an enormous adult bald eagle that was shot and reportedly scaled 8. 2 kg. Among standard linear measurements, The wing cord is 51. 5 to 69 cm, The tail is 23 to 37 cm long, And the tarsus is 8 to 11 cm. The Coleman reported ranges from 3 to 7. 5 cm, While the measurement from the gape to the tip of the bill is 7 to 9 cm. The bill size is usually variable. Alaskan eagles can have up to twice the bill length of birds from the southern United States — Georgia, Louisiana, Florida — with means including both sexes of 6. 83 cm and 4. 12 cm in Coleman length, Respectively, From these two areas. The call consists of weak staccato chirping whistles, Somewhat similar in cadence to a gull's call. The calls of young birds tend to be more harsh and shrill than those of adults. The bald eagle's natural range covers most of North America, Including most of Canada, All of the continental United States, And northern Mexico. It is the only sea eagle endemic to North America, Occupying varied habitats from the bayous of Louisiana to the Sonoran Desert and the eastern deciduous forests of Quebec and New England. Northern birds are migratory, While southern birds are resident, Remaining on their breeding territory all year. At minimum population in the 1950s, It was largely restricted to Alaska, The Aleutian Islands, Northern and eastern Canada, And Florida. From 1966 to 2015, Bald eagle numbers increased substantially throughout its winter and breeding ranges, And as of 2018 the species nests in every continental state and province in the United States and Canada. The majority of bald eagles in Canada are found along the British Columbia coast, While large populations are found in the forests of Alberta, Saskatchewan, Manitoba, And Ontario. Bald eagles also congregate in certain locations in winter. From November until February, 1, 000 to 2, 000 birds winter in Squamish, British Columbia, About halfway between Vancouver and Whistler. In March 2024, Bald eagles were found nesting in Toronto for the first time. The birds primarily gather along the Squamish and Cheekimus rivers, Attracted by the salmon spawning in the area. Similar congregations of wintering bald eagles at open lakes and rivers, Wherein fish are readily available for hunting or scavenging, Are observed in the northern United States. It has occurred as a vagrant twice in Ireland. A juvenile was shot illegal in Fermanagh on January 11, 1973, Misidentified at first as a white-tailed eagle, And an exhausted juvenile was captured near Castle Island, County Kerry on November 15, 1987. There is also a record of it from Lynne Coren Anglesey in the United Kingdom from October 17, 1978. The provenance of this individual eagle has remained in dispute. The bald eagle occurs during its breeding season in virtually any kind of American wetland habitat, Such as seacoasts, Rivers, Large lakes or marshes, Or other large bodies of open water, With an abundance of fish. Studies have shown a preference for bodies of water with a circumference greater than 11 kilometers and lakes with an area greater than 10 kilometers squared are optimal for breeding bald eagles. A bald eagle typically requires old growth and mature stands of coniferous or hardwood trees for perching, Roosting and nesting. Tree species reportedly is less important to the eagle pair than the tree's height, Composition and location. Perhaps of paramount importance for this species is an abundance of comparatively large trees surrounding the body of water. Selected trees must have good visibility, Be over 20 meters tall, An open structure and proximity to prey. If nesting trees are in standing water, Such as in a mangrove swamp, The nests can be located fairly low, At as low as 6 meters above the ground. In a more typical tree standing on dry ground, Nests may be located from 16 to 38 meters in height. In Chesapeake Bay, Nesting trees averaged 82 centimeters in diameter and 28 meters in total height, While in Florida the average nesting tree stands 23 meters high and is 23 centimeters in diameter. Trees used for nesting in the greater Yellowstone area average 27 meters high. Trees or forests used for nesting should have a canopy cover of no more than 60% and no less than 20% and be in close proximity to water. Most nests have been found within 200 meters of open water. The greatest distance from open water recorded for a bald eagle nest was over 3 kilometers in Florida. Bald eagle nests are often very large in order to compensate for size of the birds. The largest recorded nest was found in Florida in 1963 and was measured at nearly 10 feet wide and 20 feet deep. In Florida, Nesting habitats often consist of mangrove swamps and shorelines of lakes and rivers, Pinelands, Seasonally flooded flatwoods, Hardwood swamps, And open prairies and pastureland with scattered tall trees. Favorite nesting trees in Florida are slash pines, Longleaf pines, Loblolly pines, And cypress trees, But for the southern coastal areas, Mangroves are usually used. In Wyoming, Groves of mature cottonwoods or tall pines found along streams and rivers are typically bald eagle nesting habitats. Wyoming eagles may inhabit habitat types ranging from large old-growth stands of ponderosa pines to narrow strips of riparian trees surrounded by rangeland. In southeast Alaska, Sitka spruce provided 78% of the nesting trees used by eagles, Followed by hemlocks at 20%. Increasingly, Eagles nest in human-made reservoirs stocked with fish. The bald eagle is usually quite sensitive to human activity while nesting, And is found most commonly in areas with minimal human disturbance. It chooses sites more than 1. 2 km from low-density human disturbance and more than 1. 8 km from medium to high-density human disturbance. However, Bald eagles will occasionally nest in large estuaries or secluded groves within major cities, Such as Hardtack Island on the Willamette River in Portland, Oregon, Or John Hines National Wildlife Refuge at Tinicum in Philadelphia, Pennsylvania, Which are surrounded by a great quantity of human activity. Even more contrary to the usual sensitivity to disturbance, A family of bald eagles moved to the Harlem neighborhood in New York City in 2010. While wintering, Bald eagles tend to be less habitat- and disturbance-sensitive. They will commonly congregate at spots with plentiful perches and waters with plentiful prey and in northern climes partially unfrozen waters. Alternately, Non-breeding or wintering bald eagles, Particularly in areas with a lack of human disturbance, Spend their time in various upland, Terrestrial habitats, Sometimes quite far away from waterways. In the northern half of North America, Especially the interior portion, This terrestrial inhabitance by bald eagles tends to be especially prevalent because unfrozen water may not be accessible. Upland wintering habitats often consist of open habitats with concentrations of medium-sized mammals, Such as prairies, Meadows, Or tundra, Or open forests with regular carry-on access. The bald eagle is a powerful flyer and soars on thermal convection currents. It reaches speeds of 56 to 70 km per hour when gliding and flapping, And about 48 km per hour while carrying fish. Its dive speed is between 120 and 160 km per hour, Though it seldom dives vertically. Regarding their flying abilities, Despite being morphologically less well-adapted to faster flight than golden eagles, Especially during dives, The bald eagle is considered surprisingly maneuverable in flight. Bald eagles have also been recorded catching up to and then swooping under geese in flight, Turning over and thrusting their talons into the other bird's breast. It is partially migratory depending on location. If its territory is accessed open water, It remains there year-round, But if the body of water freezes during the winter making it impossible to obtain food, It migrates to the south or to the coast. A number of populations are subject to post-breeding dispersal, Mainly in juveniles. Florida eagles, For example, Will disperse northwards in the summer. The bald eagle selects migration routes which take advantage of thermals, Updrafts, And food resources. During migration, It may ascend in a thermal and then glide down, Or may ascend in updrafts created by wind against a cliff or other terrain. Migration generally takes place during the daytime, Usually between the local hours of 8 a. M. And 6 p. M. , When thermals are produced by the sun. The bald eagle is an opportunistic carnivore with the capacity to consume a great variety of prey. Fish often comprise most of the eagle's diet throughout their range. In 20 food habit studies across a species range, Fish comprise 56% of the diet of nesting eagles, Birds 28%, Mammals 14%, And other prey 2%. More than 400 species are known to be included in the bald eagle's prey spectrum, Far more than its ecological equivalent in the old world, The white-tailed eagle, Is known to take. Despite its considerably lower population, The bald eagle may come in second amongst all North American excipitrids, Slightly behind only the red-tailed hawk and number of prey species recorded. To hunt fish, The eagle swoops down over the water and snatches the fish out of the water with its talons. They eat by holding the fish in one claw and tearing the flesh with the other. Eagles have structures on their toes called spicules that allow them to grasp fish. Osprey also have this adaptation. Bird prey may occasionally be attacked and flied, With prey up to the size of Canadian geese attacked and killed in mid-air. It has been estimated that the gripping power, Pounds per square inch, Of the bald eagle is ten times greater than that of a human. Bald eagles can fly with fish at least equal to their own weight, But if the fish is too heavy to lift, The eagle may be dragged into the water. Bald eagles are able to swim in some cases, Dragging its catch ashore with its talons, But some eagles drown or succumb to hypothermia. Many sources claim that bald eagles, Like all large eagles, Cannot normally take flight, Carrying prey more than half of their own weight, Unless aided by favorable wind conditions. On numerous occasions, When large prey such as large fish, Including mature salmon or geese are attacked, Eagles have been seen to make contact and then drag the prey in a strenuously labored low flight over the water to a bank, Where they then finish off and dismember the prey. When food is abundant, An eagle can gorge itself by storing up to one kilogram of food in a pouch in the throat, Called a crop. Gorging allows the bird to fast for several days if food becomes unavailable. Occasionally, Bald eagles may hunt cooperatively when confronting prey, Especially relatively large prey such as jackrabbits or herons, With one bird distracting potential prey while the other comes behind it in order to ambush it. While hunting waterfowl, Bald eagles repeatedly fly at a target and cause it to dive repeatedly, Hoping to exhaust the victim so it can be caught. White-tailed eagles have been recorded hunting waterfowl in the same way. When hunting concentrated prey, A successful catch often results in the hunting eagle being pursued by other eagles and needing to find an isolated perch for consumption if it is able to carry it away successfully. They obtain much of their food as carry-on or via a practice known as kleptoparasitism, By which they steal prey away from other predators. Due to their dietary habits, Bald eagles are frequently viewed in a negative light by humans. Thanks to their superior foraging ability and experience, Adults are generally more likely to hunt live prey than immature eagles, Which often obtain their food from scavenging. They are not very selective about the condition or origin, Whether provided by humans, Other animals, Auto-accidents, Or natural causes, Of a carcass's presence, But will avoid eating carry-on where disturbances from humans are a regular occurrence. It will scavenge carcasses up to the size of whales, Though carcasses of ungulates and large fish are seemingly preferred. Wild wintering waterfowl are frequently exploited for carcasses to scavenge by immature eagles in harsh winter weather. Bald eagles also may sometimes feed on materials scavenged or stolen from campsites and picnics, As well as garbage dumps, Dump usage is habitual mainly in Alaska, And fish processing plants. In southeast Alaska, Fish comprise approximately 66% of the year-round diet of bald eagles, And 78% of the prey brought to the nest by the parents. Eagles living in the Columbia River estuary in Oregon were found to rely on fish for 90% of their dietary intake. At least 100 species of fish have been recorded in the bald eagle's diet. From observation in the Columbia River, 58% of the fish were caught alive by the eagle, 24% were scavenged as carcasses, And 18% were pirated away from other animals. In the Pacific Northwest, Spawning trout and salmon provide most of the bald eagle's diet from late summer throughout fall. Though bald eagles occasionally catch live salmon, They usually scavenge spawned salmon carcasses. Southeast Alaskan eagles largely prey on pink salmon, Coho salmon, And more locally sockeye salmon with chinook salmon. Due to the chinook salmon's large size, 12-18 kg, Average adult size, Probably being taken only as carry-on, And a single carcass can attract several eagles. Also important in the estuaries and shallow coastlines of southern Alaska are Pacific herring, Pacific sand lance, And eulachin. In Oregon's Columbia River estuary, The most significant prey species were large-scale suckers, 17. 3% of the prey selected there, American shad, 13%, And common carp, 10. 8%. Eagles living in the Chesapeake Bay and Maryland were found to subsist largely on American gizzard shad, Threadfin shad, And white bass. Floridian eagles have been reported to prey on catfish, Most prevalently the brown bullhead, And any species in the genus Hyktalarus, As well as mullet, Trout, Needlefish, And eels. Chain pickerels and white suckers are frequently taken in interior Maine. Wintering eagles in the Platte River in Nebraska preyed mainly on American gizzard shads and common carp. Bald eagles are also known to eat the following fish species, Rainbow trout, White catfish, Rock greenling, Pacific cod, Atka mackerel, Largemouth bass, Northern pike, Striped bass, Dogfish shark, And blue walleye. Fish taken by bald eagles vary in size, But bald eagles take larger fish than other piscivorous birds in North America, Typically range from 20 to 75 cm, And prefer 36 cm fish. When experimenters offered fish of different sizes in the breeding season around Lake Breton in California, Fish measuring 24 to 38 cm were taken 71. 8% of the time by parent eagles, While fish measuring 23 to 27. 5 cm were chosen only 25% of the time. At nests around Lake Superior, The remains of fish, Mostly suckers, Were found to average 35. 4 cm in total length. In the Columbia River estuary, Most preyed on by eagles were estimated to measure less than 30 cm, But larger fish between 30 and 60 cm, Or even exceeding 60 cm in length, Also taken especially during the non-breeding seasons. In Nago Lake, Eagles frequently take northern pike up to 80 cm long. They can take fish up to at least twice their own weight, Such as large mature salmons, Carps, Or even muskellunge, By dragging its catch with talons and pulled toward a shore. Much larger marine fish, Such as Pacific halibut and lemon sharks, Have been recorded among bald eagle prey, Though probably are only taken as young as small, Newly mature fish or as carry-on. Benthic fishes, Such as catfish, Are usually consumed after they die and float to the surface, Though while temporarily swimming in the open, May be more vulnerable to predation than most fish, Since their eyes focus downwards. Bald eagles also regularly exploit water turbines which produce battered, Stunned, Or dead fish easily consumed. Predators who leave behind scraps of dead fish that they kill, Such as brown bears, Gray wolves, And red foxes, May be habitually followed in order to scavenge the kills secondarily. Once North Pacific salmon die off after spawning, Usually local bald eagles eat salmon carcasses almost exclusively. Eagles in Washington need to consume 489 grams of fish each day for survival, With adults generally consuming more than juveniles, And thus reducing potential energy deficiency and increasing survival during winter. Behind fish, The next most significant prey base for bald eagles are other water birds. The contribution of such birds to the eagle's diet is variable, Depending on the quantity and the availability of fish near the water's surface. Water birds can seasonally comprise from 7% to 80% of the prey selection for eagles in certain localities. Wild birds are the most diverse group in the bald eagle's prey spectrum, With 200 prey species recorded. Bird species most preferred as prey by eagles tend to be medium-sized, Such as western grebes, Mallards, And American coots, As such prey is relatively easy for the much larger eagles to catch and fly with. American herring gull are the favorite avian prey species for eagles living around Lake Superior. Black ducks, Common eiders, And double-crested cormorants are also frequently taken in coastal Maine, And velvet scoter was dominant prey on San Miguel Island. Due to easy accessibility and lack of formidable nest defense against eagles by such species, Bald eagles are capable of preying on such seabirds at all ages, From eggs to mature adults, And they can effectively cull large portions of a colony. Along some portions of the North Pacific coastline, Bald eagles, Which had historically preyed mainly on kelp-dueling fish, And supplementary sea otter pups, Are now preying mainly on seabird colonies, Since both the fish, Possibly due to overfishing, And otters, Cause unknown, Have had steep population declines, Causing concern for seabird conservation. Because of this more extensive predation, Some biologists have expressed concern that murres are heading for a conservation collision due to heavy eagle predation. Eagles have been confirmed to attack nocturnally active burrow-nesting seabird species, Such as storm petrels and shearwaters, By digging out their burrows and feeding on all animals they find inside. If a bald eagle flies close by, Water birds will often fly away en masse, Though they may seemingly ignore a perched eagle in other cases. When the birds fly away from a colony, This exposes their unprotected eggs and nestlings to scavengers such as gulls. While they usually target small to medium-sized birds, Larger seabirds, Such as great black-backed gulls and northern gannets and brown pelicans of all ages, Can successfully be taken by bald eagles. Similarly, Large water birds are occasionally prey as well, Geese such as wintering emperor geese and snow geese, Which gather in large groups, Sometimes becoming regular prey. Smaller rossas geese are also taken, As well as large-sized Canadian geese. Predation on the largest subspecies has been reported. Large wading birds can also fall prey to bald eagles. For the great blue herons, Bald eagles are their only serious enemies of all ages. Slightly larger sandhill cranes can be taken as well. While adult whooping cranes are too large and formidable, Their chicks can fall prey to bald eagles. They even occasionally prey on adult tundra swans. Young trumpeter swans are also taken, And an unsuccessful attack on an adult swan has been photographed. Bald eagles have been recorded as killing other raptors on occasion. In some cases, These may be attacks of competition or kleptoparasitism on rival species, But end with consumption of the dead victims. Nine species each of other excipitrids and owls are known to have been preyed upon by bald eagles. Owl prey species have ranged in size from western screech owls to snowy owls. Larger diurnal raptors known to have fallen victim to bald eagles have included red-tailed hawks, Peregrine falcons, Northern goshawks, Ospreys, And black and turkey vultures. American preys are generally less frequently taken than fish or avian prey. However, In some regions, Such as landlocked areas of North America, Wandering bald eagles may become habitual predators of medium-sized mammals that occur in colonies or local concentrations, Such as prairie dogs and jackrabbits. Bald eagles in Seed Scotty National Wildlife Refuge often hunt in pair to catch rabbits and prairie dogs. They can attack and prey on rabbits and hares of nearly any size, From marsh rabbits to black and white-tailed jackrabbits and arctic hares. In San Luis Valley, White-tailed jackrabbits can be important prey. Additionally, Rodents such as montane voles, Brown rats, Muskrats, Nutrias, And various squirrels are taken as supplementary prey. Even American porcupines are reportedly attacked and killed.

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