The Steller's sea eagle is one of the largest birds of prey, and its size is the first thing to measure. It is named after Georg Steller, a German biologist who explored Kamchatka and Alaska in the 1700s, and its genus name, Haliaeetus, expresses that the principal diet of sea eagles is fish. It is the largest of the sea eagles and is called the heaviest known eagle, and it ranks with the harpy eagle and the Philippine eagle among the largest birds of prey. Female Steller's sea eagles are larger than the males. Animal Diversity Web gives the average mass as 6 kilograms for males and 9 kilograms for females, and a 2009 paper from a Hokkaido wildlife center gives the mass as 5 to 7.5 kg and the body length as 89 cm (male) to 100 cm (female).
The eagle's body is built for catching and eating fish. Its big bill is described as hatchet-like and is suited to tough salmon skin, and it uses both eyes together, called binocular vision, to judge where its food is. It hunts from a perch or while flying and catches prey in its talons, and sometimes it stands in shallow water or on ice and grabs fish that swim by. It eats mostly salmon, and also crabs, shellfish, small animals, gulls and carrion, and it will sometimes steal food from other birds. It can use up an entire day's calories by flying for just 45 minutes, so it nests close to its food to save energy. Researcher Alexander Ladyguin says eagles need about 11 minutes of undisturbed feeding time in winter, and four times that in summer, to meet their daily energy needs.
How many Steller's sea eagles there are is not known exactly, because scientists know little about them and their homes in the Russian Far East are remote. No one knows for sure how long they live in the wild. As of November 2026, estimates of the world population differ: 3,600 to 3,800 birds (BirdLife International, 2016) or 6,000 to 7,000 (Masterov and others, 2018). As of November 2026, another estimate puts them at around 5,000 birds, and several sources say the number is declining. As of November 2026, the IUCN Red List lists the eagle as Vulnerable, and logging that harms their forest habitat is named as a threat. The eagles are protected by law in Russia, Japan, China and South Korea, and a 2008 magazine report said about 10 percent of their nesting and wintering grounds are protected in nature preserves in Russia and Japan.
Breeding is measured by counting fledglings, the young birds that leave the nest, in each nesting territory. From 2004 to 2019, researchers monitored 438 nesting territories on Sakhalin Island and 350 on the Lower Amur over 12 field seasons in each area, and they count nesting territories rather than single nests: nests closer than 400 meters to each other were counted as one territory. One territory produced 0.51 fledglings a year on the Lower Amur and 0.35 a year on Sakhalin Island. Studies in 2004-2017 on Sakhalin and in the Amur region found about 0.53 and 0.61 fledglings per occupied territory a year, compared with about one in earlier decades. A full clutch holds one or two eggs, rarely three, and a third nestling usually does not survive even if it hatches.
A population model asks what low breeding could mean for the eagles' numbers. As of November 2026, the model predicts the Sakhalin and mainland populations would be halved in 89 and 70 years if breeding stays as low as it was in 2004-2017. The researchers estimated that only 13 to 17% of Steller's sea eagles survive to maturity, estimated indirectly with an ageing model and the age ratio of birds seen. The model suggests fecundity, the number of fledglings per adult per year, would have to rise to 0.241 on Sakhalin, or 0.33 on the mainland, to stabilize the populations. A 2020 study noted that adult survival has long been believed to be the most important factor in long-lived large raptors, with productivity of secondary importance. A 2022 study of two breeding populations said more research and data analysis are needed to explain the low breeding performance.
Satellite tags are how scientists follow young eagles to places that are hard to reach. Researchers use satellite tracking because the places where the eagles live are so remote, and Kamchatka was a key Soviet military outpost that was off-limits to scientists until the mid-1980s. Conservation research began in 1992 at Russia's Magadan State Nature Reserve, and in 2006 the San Diego Zoo and Natural Research Ltd. joined Russian scientists to study the movements of young eagles. In 1997 and 1998 scientists fitted 29 Steller's sea eagle nestlings with satellite transmitters, each weighing about 65 grams and worn like a backpack on a Teflon ribbon, with a sewn link meant to wear away so the pack falls off. Twenty-four of them gave useful data about what they did after leaving the nest.
The tracks show where the young eagles go after they leave the nest. In the 1997-98 satellite study, 19 young eagles were followed south and 16 of them reached wintering areas. Young eagles left the area around the nest between 9 September and 6 December, and most left between 14 September and 21 October. Most birds from Magadan and the Amur migrated down the western edge of the Okhotsk Sea, while birds raised in Kamchatka moved down the Kuril Islands. Tracked eagles from Magadan crossed an average of 11.6 degrees of latitude on migration, compared with 2.1 for eagles from Kamchatka and 1.1 for Sakhalin. Before migrating, young eagles stopped at pre-migration sites on the lower parts of rivers, which may be places where many dead salmon are found after spawning, and they spent winter in one to three subareas, which averaged 274, 529 and 1,181 square kilometers.
On Hokkaido, the eagles' winter food is tied to deer and to lead. When fish became harder to find in winter, dead deer became a major food for Steller's sea eagles wintering on Hokkaido, according to a 2009 paper, and a satellite-tracking study found that 35% of eagles overwintering in Hokkaido used mountain areas for at least some time, where they scavenge deer. Lead poisoning of Steller's sea eagles in Japan was first confirmed in 1996, and by 2007, 129 Steller's and white-tailed eagles had been diagnosed as lead poisoning fatalities in Japan. Hokkaido began banning lead rifle bullets for hunting sika deer in 2000 and lead shot pellets in 2001, extended the ban in 2004 to all hunting of large animals, and since 2014 hunters may not even carry lead rifle bullets, slugs or large shot pellets.
Lead is measured in the birds themselves, and the results are still being weighed. As of November 2026, a 2015-2018 study of birds found dead in Japan found that 9 of 34 (26.5%) had liver lead above the level for lead poisoning, and an earlier study found that 42% of Steller's sea eagles (18 of 43) tested from 2004 to 2015 in Hokkaido had lead above the poisoning level. Scientists use lead isotope ratios to find the source of lead in a bird, because the ratios differ among rifle bullets, shot pellets and fishing sinkers. As of November 2026, the 2015-2018 study concluded that eagles in Hokkaido are still exposed to lead because of the illegal use of lead ammunition. The effect of lead on the whole population is hard to measure because no one knows how many eagles have died during migration or in the Russian breeding range.
The year ends where it starts, at the nest, and a Steller's sea eagle's nest is huge. A pair often returns to the same nest each year and adds more branches to it, and a nest can be 1.8 to 2.4 meters (6 to 8 feet) wide. The eggs take about 38 to 45 days to hatch, and a pair usually raises just one chick. A chick is covered in soft gray-white down that slowly changes to brown feathers, and it learns to fly when it is about 10 weeks old. By the time a chick is five weeks old, it eats about one pound (0.4 kilograms) of fish a day. Researcher Alexander Ladyguin found that nestlings multiply their weight 40 times in less than two months on a diet of salmon.
Words to know
- fecundity: breeding output
- fledglings: young flyers
- isotope: kind of atom
- raptors: birds of prey
- transmitters: signal senders
