Steller’s sea eagle (Haliaeetus pelagicus): Largest eagle of the North Pacific

The Steller’s sea eagle (Haliaeetus pelagicus) is a massive raptor endemic to coastal northeastern Asia. One of the heaviest eagles, it relies primarily on fish. Listed as Vulnerable, it faces threats from habitat loss, overfishing, and lead poisoning, posing serious conservation challenges.

Discovery

The Steller’s sea eagle was first observed and documented by Georg Wilhelm Steller, a German naturalist and physician, during the Great Northern Expedition (1733-1743) led by Vitus Bering. Steller recorded the species in Kamchatka, noting its large size, coastal habits, and reliance on fish.

The species was formally described in 1811 by Peter Simon Pallas, a Prussian naturalist, who classified it as Aquila pelagica. The species name pelagica derives from the Ancient Greek pelagos, meaning “open sea” or “ocean.” Subsequent taxonomists assigned alternative names, including Falco leucopterus (C. J. Temminck, 1824) and Falco imperator (H. von Kittlitz, 1832). It was ultimately placed in its current genus, Haliaeetus, by George Robert Gray in 1849, following a broader reclassification that distinguished sea eagles from other raptors. The common name, Steller’s sea eagle, honors G. W. Steller, in recognition of his early observations. The species is also known as Steller’s fish eagle, Pacific sea eagle, or white-shouldered eagle.

Genetic studies have provided insight into the species’ evolutionary history. A 1996 analysis of cytochrome b mitochondrial DNA revealed that Haliaeetus pelagicus diverged from a lineage that also produced the bald eagle (Haliaeetus leucocephalus) and white-tailed eagle (Haliaeetus albicilla) approximately 3-4 million years ago. All three species share yellow beaks, talons, and eyes, distinguishing them from their closest known relative, Pallas’s fish eagle (Haliaeetus leucoryphus).

Taxonomically, Haliaeetus pelagicus is a monotypic species, with no recognized subspecies. However, a dark-plumaged form historically referred to as H. p. niger was described in Korea, where individuals were reportedly resident year-round. The last sighting of this form was in 1968, and a dark-colored female eagle matching its description was hatched in captivity in 2001. However, genetic analysis and subsequent breeding records suggest that H. p. niger represents a rare dark morph rather than a distinct subspecies.

Recent studies have focused on breeding success, conservation genetics, and environmental threats. In 2020, M. S. Romanov and V. B. Masterov identified low reproductive success as a major driver of population decline, while Saeki et al. (2000) highlighted lead contamination in eagles wintering in Hokkaido. Long-term tracking efforts continue to monitor migration patterns and habitat changes to support conservation planning.

Identification

The Steller’s sea eagle is among the largest and heaviest birds in the world, characterized by its dark plumage, massive yellow beak, and prominent white markings. It displays strong sexual dimorphism, with females being significantly larger than males. Adult birds typically measure between 85 and 105 centimeters (2.8-3.4 feet) in length, with a wingspan ranging from 2 to 2.7 meters (6.6-8.8 feet). While the average wingspan is around 2.5 meters (8.2 feet), there are unverified reports suggesting individuals may reach 2.75 or even 2.8 meters (9-9.2 feet), making it the largest living eagle. However, these extreme measurements remain a subject of debate due to the lack of confirmed specimens.

Males weigh between 5 and 6.8 kilograms (11-15 pounds), whereas females are considerably heavier, reaching 7.5 to 9.5 kilograms (16.5-20.9 pounds) and occasionally exceeding this mark. The Steller’s sea eagle possesses an exceptionally large and robust bill, adapted for tearing apart fish and carrion. The culmen length ranges from 62 to 75 millimeters (2.4-3 inches), while the bill from the gape to the tip measures around 117 millimeters (4.6 inches), making it one of the most imposing bills among all eagle species.

Adult Steller’s sea eagles have predominantly black plumage with contrasting white patches on the shoulders, thighs, tail, and forehead. Their wedge-shaped tail measures between 32 and 40 centimeters (12.6 to 15.7 inches), distinguishing the species from the closely related white-tailed sea eagle (Haliaeetus albicilla), which has a more rounded tail. Their massive beak, along with their legs and cere, is bright yellow, standing out against their dark body.

Juveniles differ significantly from adults, undergoing a gradual transition to full adult plumage over a period of approximately five years. Young birds are mostly dark brown, lacking the bold white patches seen in adults. Their tail is darker, with faint white mottling, and their beak is initially blackish-gray, progressively lightening to yellow with age. Their legs start as a pale whitish-gray before becoming bright yellow as they mature, while the iris transitions from dark brown in juveniles to a lighter shade in adults.

The first-year plumage, known as the juvenal phase, is entirely dark brown with white feather bases and subtle mottling on the tail. As they progress through their second to fourth years, white feathering increases on the wings and tail, while the bill and eyes gradually lighten. By the fifth year or later, individuals acquire their full adult coloration, with well-defined white patches and a fully yellow beak and legs. Immature Steller’s sea eagles are sometimes confused with juvenile white-tailed sea eagles, but they can be distinguished by their heavier build, more pronounced beak, and wedge-shaped tail.

Vocalization

The Steller’s sea eagle is generally silent outside of the breeding season but becomes more vocal during courtship, territorial disputes, and nesting interactions. Its primary call consists of a harsh, rasping series of repeated “ka-ka-ka” or “kra-kra-kra” sounds, often delivered in short bursts. During courtship displays, males emit a sequence of high-pitched cries, sometimes in coordination with aerial maneuvers. Nesting pairs communicate using softer whistles and chirps, particularly between the female and her offspring. Alarm calls are more urgent and sharper, resembling the vocalizations of the white-tailed sea eagle but with a deeper tone. These calls can carry over long distances in open coastal areas, especially when used in response to intruders or rival eagles.

Range

The Steller’s sea eagle is native to the Russian Far East, where it breeds along coastal regions, river valleys, and large inland lakes. Its breeding range extends across northeastern Russia, with the highest nesting densities found on the Kamchatka Peninsula, the lower Amur River basin, the Shantar Islands, northern Sakhalin Island, and the coastal areas bordering the Sea of Okhotsk.

After the breeding season, most individuals migrate south, although some remain near their nesting areas if food availability and environmental conditions permit. The largest wintering population is found in Japan, particularly on Hokkaido, where eagles congregate along coastal ice, rivers, and fishing ports. Smaller numbers winter on Honshu. Others remain in southern Kamchatka or migrate to the Kuril Islands, especially Kunashir and Iturup, where open water allows access to fish. Some individuals also winter in northeastern China, mainly in Heilongjiang and Liaoning provinces, as well as in North and South Korea. Estimates suggest that approximately 2,000 Steller’s sea eagles winter in Japan, making it the most important location for the species outside of Russia.

Although the species is generally restricted to northeastern Asia, vagrancy has been recorded. Rare but well-documented sightings have occurred in Alaska, Canada, and the northeastern United States, including Maine, Massachusetts, and even as far south as Texas. In Europe, occasional records have been documented in Scandinavia, particularly in Norway, and in the Netherlands. These extralimital occurrences are thought to be the result of dispersing juveniles or birds that have been displaced by storms.

Migration

The Steller’s sea eagle exhibits partial migratory behavior, with some individuals remaining near their breeding sites year-round while others travel long distances to wintering grounds. Juvenile dispersal begins between September and December, peaking from mid-September to late October. Satellite tracking studies indicate that migrating juveniles travel at an average speed of 48 kilometers (29.8 miles) per day when excluding stopovers, or 23 kilometers (14.3 miles) per day when stopovers are included. Migration duration varies significantly, ranging from as little as four days to as long as 116 days, depending on environmental conditions and individual movement patterns.

The primary migration routes follow the coastlines of the Sea of Okhotsk and the Kuril Islands. Many birds travel southward through Sakhalin before reaching Hokkaido, where they remain for the winter months. Some individuals have been tracked covering distances of over 1,800 kilometers (1120 miles) from their breeding sites. Winter range sizes vary among individuals, with most birds establishing one to three subareas within their wintering grounds. First-year wintering areas average around 275 square kilometers (106 square miles), while by the second winter, some individuals expand their ranges to as much as 1,180 square kilometers (456 square miles). Juveniles tend to shift their wintering locations southward after their first year.

Spring migration begins between February and late March, with most eagles returning to their breeding grounds by mid-May. Adult Steller’s sea eagles exhibit strong site fidelity, returning to the same nesting territories each year. In contrast, juveniles often wander widely before eventually settling into breeding territories later in life.

Habitat

The Steller’s sea eagle inhabits coastal regions, river valleys, and large inland water bodies, relying on areas with abundant fish populations. It requires mature forests, cliffs, or isolated trees for nesting and prefers locations with minimal human disturbance. Habitat use varies between the breeding season and winter months, reflecting the species’ dependence on seasonal food availability.

During the breeding season, the species is found in the Russian Far East, occupying coastal cliffs, riverine forests, and islands along major rivers. Nesting occurs primarily in mixed or coniferous forests, where large trees such as birch, larch, poplar, and aspen provide stable nesting platforms. These trees are typically located near estuaries, lakes, and slow-moving rivers, ensuring proximity to fish stocks. While the species is generally associated with coastal environments, certain populations breed up to 100 kilometers (62 miles) inland along major rivers. In Kamchatka, nests are often built in park-like stands of Erman’s birch, while along the lower Amur River and Sakhalin, eagles prefer larches and floodplain forests. Nests are typically placed 15 to 20 meters (50-65 feet) above the ground, often in trees with dead or broken tops, which provide an open platform for landing and takeoff. In regions where tall trees are scarce, some pairs construct nests on rocky cliffs overlooking rivers or coastal waters.

In winter, habitat selection is more variable. While some individuals remain near their breeding sites if food sources are available, most migrate southward to Japan, the Kuril Islands, and northeastern China, where they concentrate around coastal fishing grounds, ice-free river mouths, and open water lakes. On Hokkaido, wintering eagles are frequently seen along coastal ice, harbors, and estuaries, where they scavenge fish discarded by fisheries. Inland, they may forage near lakes and marshes or follow rivers where fish carcasses accumulate. In addition to fish, wintering eagles often rely on carrion, including the remains of marine mammals, deer, and seabirds, making them opportunistic scavengers.

Habitat use is influenced by seasonal fish movements. During autumn, eagles forage along rivers where salmon are spawning, taking advantage of dead or weakened fish. By mid-winter, when most rivers freeze, those remaining in Russia shift to coastal waters, where they hunt for fish trapped in ice holes or feed on stranded seabirds. On Hokkaido, some individuals move inland to mountainous areas, where they scavenge on sika deer carcasses left by hunters. The species’ dependence on aquatic ecosystems makes it highly vulnerable to habitat degradation, particularly due to deforestation, overfishing, and climate-related changes to river flow and ice cover.

Behavior

The Steller’s sea eagle is a powerful and dominant raptor, exhibiting both solitary and social behaviors depending on the season and food availability. During the breeding season, it maintains large territories, with nesting pairs defending their sites aggressively. These birds are typically solitary or found in pairs while nesting, though they may tolerate other Steller’s sea eagles at a distance.

Outside the breeding season, the species’ behavior becomes more flexible, and it frequently aggregates around abundant food sources. Wintering populations, particularly in Hokkaido, gather in large numbers near coastal fisheries, where they scavenge discarded fish. The degree of social interaction varies; while they tolerate proximity at feeding sites, dominance hierarchies emerge, with larger individuals outcompeting weaker or younger birds.

Interactions with other species

Steller’s sea eagles frequently interact with other raptors and scavengers, particularly the white-tailed eagle (Haliaeetus albicilla), which shares much of its range. While Steller’s sea eagles are larger and often dominate in direct encounters, white-tailed sea eagles are more numerous and adaptable, leading to competition in areas where resources are limited. On Kamchatka, both species may nest in the same general area, but white-tailed eagles tend to predominate in locations where Steller’s sea eagles are less frequent.

In winter, Steller’s sea eagles form mixed foraging groups with white-tailed sea eagles and black kites (Milvus migrans), particularly at fish-rich sites in Japan. These interactions often involve kleptoparasitism, with Steller’s sea eagles stealing fish from smaller raptors. Large corvids, such as the large-billed crow (Corvus macrorhynchos), also compete with eagles for carrion, sometimes harassing them to take advantage of food sources. While interactions with golden eagles (Aquila chrysaetos) and gyrfalcons (Falco rusticolus) have been recorded in overlapping areas, direct competition is rare, as these species occupy different ecological niches.

Beyond avian competitors, Steller’s sea eagles sometimes scavenge alongside terrestrial mammals, particularly in coastal and tundra environments. They have been observed feeding on seal and sea lion carcasses along the Russian coast, occasionally competing with scavengers such as foxes and wolverines. In Hokkaido, wintering birds frequently take advantage of Sika deer remains left by hunters, though this behavior has led to lead poisoning from ammunition ingestion.

Foraging and human interactions

Steller’s sea eagles exhibit versatile foraging behavior, with a preference for hunting live fish but a strong reliance on scavenging when necessary. They often perch near water, scanning for fish before executing short, powerful dives to seize prey from the surface. In winter, when live prey is scarce, they shift to scavenging, relying on salmon carcasses, fishery waste, and carrion. Unlike some raptors, they do not engage in prolonged aerial pursuits but instead use their powerful talons and beak to secure and tear apart food.

The species has a complex relationship with humans, influenced by both cultural significance and conservation challenges. In Japan and Russia, Steller’s sea eagles are admired and protected, featuring prominently in Ainu folklore and Russian conservation campaigns. However, human activities also pose significant threats, particularly through deforestation, industrial pollution, and overfishing. The eagles have adapted to wintering near fishing ports and settlements, where they benefit from discarded fish, but this also exposes them to risks such as entanglement in fishing gear and contamination from pollutants. In Hokkaido, wildlife tourism has increased tolerance toward human presence, as eagles are frequently observed and photographed at winter feeding sites. In Russia, however, habitat destruction due to logging and hydroelectric development continues to displace breeding populations.

Breeding

The Steller’s sea eagle is a monogamous species, forming long-term pair bonds that are maintained across multiple breeding seasons. The breeding period varies depending on climate and food availability, with pairs returning to their nesting sites between late February and early March. Courtship displays, including vocalizations, aerial maneuvers, and mutual feeding, take place before copulation, which typically occurs at the nest site. Nest-building begins in early spring, and the first eggs appear by mid-April, although some pairs lay as late as the end of May.

Nests are large and constructed from thick branches and twigs, often positioned in the tallest available trees. Many pairs maintain multiple nests, alternating between them from year to year, with secondary nests typically located within 900 meters (3,000 feet) of the primary site. While nests are reused for multiple breeding seasons, they are frequently expanded, sometimes reaching up to 2 meters (6.5 feet) in diameter over time.

Clutch size varies from one to three eggs, though two eggs are most common. The incubation period is estimated to last more than 34 days, beginning with the first egg, which leads to asynchronous hatching. As a result, the first chick to hatch has a competitive advantage over its siblings, which often struggle to survive in years of food scarcity. Hatchlings emerge between mid-May and mid-June, and fledging occurs from August to early September.

Newly hatched chicks are covered in soft white down, which is soon replaced by a darker smoky brown-gray second down as they grow. They remain entirely dependent on their parents for food and protection for the first several weeks. Feathers begin to emerge around four to six weeks after hatching, and by eight to ten weeks, the young eagles are nearly fully feathered. Their juvenile plumage is mostly dark brown, with mottled white markings on the retrices (tail feathers), while their beak remains dark gray to black rather than the bright yellow seen in adults.

Both parents participate in feeding and protecting the young. The female spends the majority of the time at the nest, brooding the chicks and tearing food into small pieces for them to eat. The male is primarily responsible for hunting and delivering prey, though he may also assist in feeding. As the chicks grow, both parents bring whole fish to the nest, allowing the young eagles to learn how to handle and tear apart food themselves.

Fledging occurs between 10 and 11 weeks after hatching, with most chicks leaving the nest by late August or early September. However, they remain dependent on their parents for several more weeks, staying within the breeding territory as they continue learning to hunt. Young eagles often remain in their parents’ territory until at least October, after which they begin dispersing to wintering grounds.

Breeding success has declined in recent decades, with productivity decreasing from an average of 0.8 to 1.4 fledglings per occupied nest in the 1980s–90s to 0.53-0.61 fledglings per nest in recent years. In certain years, as many as 30-60% of territorial pairs skip breeding altogether, particularly when environmental conditions are poor. The primary causes of nest failure include predation by brown bears, food shortages, severe weather, and human disturbance. In Sakhalin, brown bears are the most significant nest predators, often climbing trees to consume eggs and nestlings, while in Kamchatka, sable and ermine occasionally raid nests. Despite these challenges, Steller’s sea eagles exhibit strong site fidelity, with many pairs returning to the same nesting territories year after year.

While the species remains relatively abundant, declining breeding success has raised concerns about long-term population stability. Conservation efforts focusing on habitat protection, food availability, and minimizing human disturbance are crucial to maintaining healthy breeding populations.

Lifespan

The Steller’s sea eagle is a long-lived raptor, with individuals in the wild typically reaching 20 to 25 years. In captivity, where threats such as predation, food shortages, and environmental stressors are absent, they can live beyond 30 years, with some reaching up to 35-40 years.

Juvenile survival rates are relatively low, with studies estimating that only 14-19% of fledglings survive to adulthood. The first two years of life are the most critical, as young eagles must develop their hunting skills while avoiding threats such as food scarcity, predation, and environmental hazards. Those that reach maturity have a high survival rate, as adult mortality is generally low in stable populations.

Several factors impact lifespan and survival. Lead poisoning from scavenged carcasses containing lead ammunition is a growing concern, particularly in Hokkaido, Japan, where wintering eagles frequently feed on deer remains left by hunters. Habitat degradation, overfishing, and industrial pollution also pose long-term risks, reducing prey availability and increasing exposure to contaminants such as PCBs and heavy metals. In some regions, collisions with power lines have been documented, though this threat is less severe compared to other human-related impacts.

Despite these challenges, the species’ low reproductive rate and long lifespan indicate a K-selected life history strategy, where survival of adult individuals plays a greater role in maintaining population stability than high reproductive output. Conservation efforts aimed at reducing juvenile mortality and mitigating human-induced threats are crucial to ensuring long-term survival.

Diet

The Steller’s sea eagle is an opportunistic predator and scavenger, with a diet primarily consisting of fish, supplemented by birds, mammals, invertebrates, and carrion. Its feeding habits are strongly influenced by seasonal prey availability, with salmon runs playing a particularly important role in shaping its distribution and foraging behavior.

Fish make up the majority of the species’ diet, with Pacific salmon (Oncorhynchus spp.) being the most significant food source across much of its range. The availability of salmon dictates the eagle’s seasonal movements, as individuals gather in large numbers near spawning waters to exploit both live and dead fish. In Kamchatka, peak feeding aggregations occur during August and September, when hundreds of eagles can be observed feeding communally on salmon.

During the breeding season, parents bring fish measuring 20-30 centimeters (8-12 inches) to their nestlings, with 2-3 feeding deliveries per day. In late summer and autumn, eagles consume spent fish that have died after spawning, often picking carcasses from riverbanks and shallows.

Winter diet and seasonal shifts

In winter, when salmon become scarce, the species shifts to alternative fish sources, such as cod (Gadus macrocephalus) in Japanese waters, particularly in the Rausu Sea and Nemuro Straits. These fisheries provide a critical winter food source, with commercial fishing activities inadvertently supplying eagles with discarded fish.

Recent studies in Hokkaido have revealed a more complex seasonal foraging pattern. In early winter (November-December), most eagles remain near river basins, feeding on salmon carcasses. However, by mid-February to March, eagles shift from rivers to coastal areas, lakes, estuaries, and even refuse dumps, adapting to changing food availability.

At Furen Lake, eagles rely on discarded fish from ice fisheries, but observations suggest that the number of eagles present does not always match the amount of discarded fish, indicating possible food shortages in some years.

Additionally, an increasing number of eagles have been observed scavenging sika deer (Cervus nippon) carcasses left by hunters, a behavior that has led to lead poisoning from ingesting bullet fragments.

Birds, mammals, and invertebrates

When fish are unavailable, Steller’s sea eagles prey on waterbirds, including ducks, gulls, and auks. In Kamchatka, before the salmon arrive, ducks and gulls can make up 50-70% of the diet for nestlings. Along the Amur River, the summer diet consists of approximately 80% fish, 10% birds, and 5% mammals. Eagles hunt birds by ambushing them on the water’s surface or snatching them in mid-flight.

Mammals form a smaller portion of the diet but become important in winter. The species is known to take hares, sable, ermine, and foxes, sometimes stealing animals from traps set by commercial hunters. Carrion from seals and sea lions is also consumed along coastal areas, especially by younger eagles.

In coastal environments, invertebrates such as crabs, sea urchins, mussels, and squid are occasionally eaten, particularly by juvenile eagles still developing hunting skills.

Hunting and foraging strategies

Steller’s sea eagles employ multiple hunting techniques, adapting to their environment and prey availability. The most common method involves perch-hunting, where an eagle waits on a tree or rocky ledge 5-30 meters (16-100 feet) above the water, scanning for fish before making a direct dive to capture prey with its talons. They may also hunt on the wing, circling 6-7 meters (20-23 feet) above the water before diving.

Another strategy involves standing in shallow water on sandbanks, spits, or ice floes, where the eagle grabs passing fish with its talons. This technique is especially common during salmon spawning season, as eagles take advantage of weakened or dead fish in shallow waters.

Steller’s sea eagles frequently engage in kleptoparasitism, stealing food from other birds. This behavior is particularly common in communal feeding sites, where individuals attempt to snatch fish from white-tailed eagles (Haliaeetus albicilla), golden eagles (Aquila chrysaetos), or black kites (Milvus migrans). Juveniles rely on kleptoparasitism more than adults, but they are often challenged and driven away by dominant individuals.

Seasonal and regional variations

The species’ diet fluctuates based on seasonal prey availability. In Kamchatka, salmon runs drive feeding behavior, while in Hokkaido, wintering eagles shift to marine fish from fisheries. Along the lower Amur River, summer diets are heavily fish-based, whereas winter diets may include small mammals and carrion. In coastal areas, young eagles rely more on marine carrion and invertebrates, while adults focus on live prey.

Although Steller’s sea eagles are capable predators, they are also highly adaptable scavengers, making them less vulnerable to temporary food shortages but more susceptible to human-related threats, such as contamination from fishing byproducts, lead poisoning from scavenged carcasses, and reduced fish stocks due to overfishing.

As winter conditions change, eagles are becoming increasingly reliant on human-influenced food sources, which presents new conservation challenges for the species.

Culture

The Steller’s sea eagle holds cultural importance in Japan and Russia, particularly among indigenous Arctic and Siberian communities. Among the Ainu people of Japan, large raptors like the Steller’s sea eagle were seen as spiritual beings, possibly serving as divine messengers in local traditions. While specific legends about the species are scarce, its presence in Ainu oral culture suggests that it was regarded with reverence. In Siberian and Far Eastern Russian indigenous traditions, eagles are often seen as symbols of strength, wisdom, and protection, with some Nanai and Evenk tribes believing they act as messengers between the earth and the sky.

Today, the Steller’s sea eagle serves as a flagship species for conservation in Russia and Japan, representing the health of coastal and river ecosystems. In Russia, it is widely used in national wildlife campaigns, particularly in Kamchatka, where its presence is closely tied to salmon populations. In Japan, it is a major attraction for wildlife tourism, especially in Hokkaido, where birdwatchers and photographers gather each winter in locations such as Rausu and the Nemuro Strait to see the eagles perched on drift ice.

Beyond conservation and ecotourism, the species has been occasionally kept in zoos and raptor centers, where its impressive size and striking plumage make it a popular subject for public awareness programs. While not commonly used in falconry, it has gained recognition as a symbol of East Asian wilderness, reflecting the fragile balance of coastal and marine ecosystems. Its reliance on salmon stocks and fisheries has also positioned it as an ecological indicator, with declining populations highlighting broader environmental challenges such as overfishing, habitat destruction, and pollution.

Threats and conservation

The Steller’s sea eagle is classified as Vulnerable by the IUCN, with an estimated global population of 3,500 to 4,500 mature individuals, including 1,700-1,800 breeding pairs. The breeding population is concentrated in Russia’s Far East. Long-term monitoring indicates declining reproductive success, with fledging rates dropping from 1.0 fledgling per nest in the 1980s to an average of 0.55 fledgling per occupied nest in recent years. In some areas, 30-60% of territorial pairs skip breeding altogether in unfavorable years.

Threats

The loss and degradation of breeding and foraging habitats pose a major challenge for the species. In Russia, logging and large-scale infrastructure projects, such as hydroelectric developments and petrochemical industry expansions, have led to deforestation and alterations of river ecosystems. On Sakhalin Island and in the Amur region, previously high-density nesting areas are now experiencing significant declines in occupied nesting sites. In Japan, overfishing of key prey species has forced some eagles to scavenge more frequently on land, increasing their exposure to poisoning, disease, and human activity.

Lead poisoning and toxic contaminants

Lead poisoning is a major cause of mortality among wintering populations in Hokkaido, where 20-25% of dead or debilitated eagles examined between 1986 and 1997 tested positive for acute lead toxicity. Lead concentrations exceeding 70 micrograms per gram of dry weight have been found in some affected individuals, well above lethal thresholds. The ingestion of lead fragments from sika deer carcasses left by hunters has been identified as the primary cause. Despite ongoing efforts to regulate lead-based ammunition, poisoning incidents continue to threaten the estimated 2,000-2,500 Steller’s sea eagles wintering in Japan.

Recent studies also indicate potential risks from other heavy metals and environmental pollutants. Mercury and cadmium levels detected in the liver and kidneys of some dead or debilitated eagles suggest exposure to marine pollution and industrial contaminants. While these levels are generally below lethal thresholds, continued exposure could have long-term physiological and reproductive effects on eagle populations.

Dependence on human-influenced food sources

Observations in Hokkaido reveal that wintering Steller’s sea eagles have become increasingly reliant on human-related food sources, including fishery byproducts, refuse dumps, and deer carcasses. This dependence may expose eagles to pollutants, plastic ingestion, and food shortages when human activities fluctuate. Studies show that discarded fish from ice fisheries at Furen Lake are a major food source, but not always sufficient to support the local eagle population.

Additionally, some eagles have been observed scavenging waste from urban and industrial refuse sites, increasing their risk of ingesting harmful materials. This emerging shift in foraging behavior could have long-term consequences, particularly if natural food sources continue to decline.

Avian pox and emerging diseases

An emerging risk is avian pox, which was first detected in a Steller’s sea eagle in Japan. The affected bird exhibited cutaneous lesions and necrotic skin, with secondary infections weakening its condition. The disease, caused by Avipoxvirus, has been recorded in various raptors worldwide, but its impact on Steller’s sea eagle populations remains unknown.

Given that infectious diseases can spread more easily in concentrated populations, eagles wintering in densely populated feeding areas, such as fisheries and refuse sites, may be at a higher risk of disease outbreaks. Continued monitoring of pathogen transmission and disease prevalence is necessary to assess the long-term impact on population health.

Predation and nest failures

Predation by brown bears (Ursus arctos) on nestlings has been documented in the Russian Far East, particularly in Magadan and the North Okhotsk Sea region. Observations confirm that bears opportunistically raid nests, likely when attracted by discarded fish remains near breeding sites. Over six years of study, researchers recorded at least five cases of brown bear predation, along with claw marks on nesting trees and missing chicks.

While not a primary driver of population decline, such incidents contribute to local breeding failures, particularly in areas where human activity may inadvertently increase predator access to nesting sites. Additionally, mustelids such as sables and ermines prey on eggs, while wolverines, raccoons, and lynxes have been observed targeting nestlings in various parts of the eagle’s range.

Collisions and electrocution

Electrocution and collisions with power lines have been documented in both Russia and Japan, particularly near coastal foraging areas, where infrastructure expansion continues. Additionally, entanglement in fishing gear has been reported in some regions, increasing the risk of human-related mortality.

Conservation efforts

In Russia, Steller’s sea eagles are protected within several strict nature reserves, including the Kronotsky Biosphere Reserve and the Magadan Nature Reserve. Conservationists monitor populations and work to reduce human disturbances in critical breeding and foraging areas. However, habitat destruction caused by industrial expansion, logging, and climate-related changes remains a long-term challenge.

In Japan, conservation programs focus on reducing lead poisoning through public awareness campaigns and lead ammunition bans in key wintering areas. Wildlife rehabilitation centers, such as those in Hokkaido, treat eagles suffering from lead toxicity, though survival rates for poisoned individuals remain low.

Efforts to mitigate electrocution risks include power line modifications in high-risk areas, while fisheries management initiatives aim to sustain salmon and cod populations (key prey species for the eagle). Research continues into avian pox prevalence, long-term lead contamination effects, and the impact of environmental pollutants to inform conservation strategies.

Recent habitat restoration projects in Russia have focused on preserving mature forests near key nesting areas, but industrial expansion continues to pose a significant threat. Additionally, new research suggests that protecting communal wintering sites (particularly key foraging areas in Hokkaido and the Russian Far East) may be essential for maintaining population stability.

Despite these efforts, the species remains vulnerable. If current trends continue, models predict that some regional populations could decline by 50% within the next 70-120 years. Continued conservation action is essential to counteract habitat loss, pollution, and the increasing impact of climate change on the eagle’s prey availability.

Similar species

The Steller’s sea eagle (Haliaeetus pelagicus) shares its range with several other large eagles, particularly those in the genus Haliaeetus. While it is the largest and most distinctive of the sea eagles, it frequently interacts with closely related species, especially in its breeding and wintering grounds.

White-tailed eagle (Haliaeetus albicilla)

The white-tailed eagle is the most significant species overlapping with the Steller’s sea eagle, sharing much of its range in Russia, Japan, Korea, and China. Although slightly smaller, it occupies similar coastal and riverine habitats, often competing for fish and scavenging opportunities. Steller’s sea eagle is generally dominant in size and aggression at feeding sites, but the two species coexist, particularly in wintering areas where food is abundant. Both species exhibit a wedge-shaped white tail in adulthood, but the white-tailed eagle lacks the Steller’s sea eagle’s striking white wing patches and massive bill.

Bald eagle (Haliaeetus leucocephalus)

The bald eagle, a North American species, occasionally occurs as a vagrant in the Commander Islands and Kamchatka, where its range briefly overlaps with that of the Steller’s sea eagle. While both species share a similar ecological niche as fish-eating raptors, the bald eagle is slightly smaller and less robust. It is also easily distinguished by its white head and tail, which contrast with the Steller’s darker plumage with white wing markings. The two species do not compete frequently due to the bald eagle’s rarity in the Russian Far East.

Pallas’s fish eagle (Haliaeetus leucoryphus)

The Pallas’s fish eagle is a co-occurring species, occasionally found near the Amur River. It is significantly smaller and lighter than the Steller’s sea eagle, with brown plumage and a pale head, making it more similar in appearance to juvenile Steller’s sea eagles. Unlike the Steller’s coastal habitat preference, Pallas’s fish eagle is more closely associated with inland freshwater wetlands and lakes, feeding primarily on fish in slow-moving rivers. This species is one of the most endangered eagles in the world and is far less numerous, with only occasional records near the range of the Steller’s sea eagle.

Future outlook

The future of the Steller’s sea eagle remains uncertain. While the species persists in key breeding and wintering areas, long-term trends indicate a declining population due to habitat degradation, lead poisoning, and reduced prey availability. Climate change may further impact its foraging grounds, particularly in regions where warming temperatures affect fish populations. Without sustained conservation efforts, particularly in reducing human-caused mortality and protecting critical nesting sites, the species could experience continued decline, with some regional populations shrinking significantly within the next century.

At Planet of Birds, we recognize the Steller’s sea eagle as one of the most magnificent and ecologically significant raptors. Its presence along the rivers and coasts of the Russian Far East symbolizes the health of its ecosystem. Ensuring its survival requires a combination of habitat protection, stricter regulations on lead ammunition, and enhanced conservation awareness. As one of the world’s largest and most powerful eagles, the Steller’s sea eagle deserves stronger, long-term conservation commitments to prevent it from becoming yet another species lost to human impact.

Further reading

• M. J. Mcgrady, E. Potapov, I. G. Utekhina (2024). Brown Bear (Ursus Arctos) Feeds on Steller’s Sea Eagle (Haliaeetus Pelagicus) Nestling. Journal of Raptor Research, Volume 33, Issue 4, Article 15.
• M. S. Romanov, V. B. Masterov (2020). Low Breeding Performance of the Steller’s Sea Eagle (Haliaeetus Pelagicus) Causes the Populations to Decline. Ecological Modelling, Volume 420.
• K. Saito, M. Haridy, W. Abdo, A. El-Morsey, S. Kasem, Y. Watanabe, T. Yanai (2019). Poxvirus Infection In a Steller’s Sea Eagle (Haliaeetus Pelagicus). Journal of Veterinary Medical Science, Volume 81, Issue 2.
• E. R. Potapov, I. G. Utekhina, M. J. Mcgrady (2015). Steller’s Sea Eagle Haliaeetus Pelagicus: Display and Copulation in Early Spring. BirdingAsia 23.
• M. J. Mcgrady, M. Ueta, E. R. Potapov, I. G. Utekhina, V. B. Masterov, A. Ladyguine, V. Zykov, J. Cibor, M. Fuller, W. S. Seegar (2003). Movements by Juvenile and Immature Steller’s Sea Eagles Haliaeetus Pelagicus Tracked by Satellite. Ibis, Volume 145, Issue 2.
• E. Y. Kim, R. Goto, H. Iwata, Y. Masuda, S. Tanabe, S. Fujita (1999). Preliminary Survey of Lead Poisoning of Steller’s Sea Eagle (Haliaeetus Pelagicus) and White-Tailed Sea Eagle (Haliaeetus Albicilla) in Hokkaido, Japan. Environmental Toxicology and Chemistry, Volume 18, Issue 3.