Steller’s sea-eagle biology
The Steller's sea-eagle Haliaeetus pelagicus is the largest of all sea-eagles, weighing 11 to 20 pounds (5 to 9 kilograms) with a wingspan of 7 to 8 feet (2.2 to 2.45 meters). Like many raptors, female Steller’s sea-eagles are generally larger
than the males. Despite its large size,
attractive appearance, and exotic range, the ecology of the Steller's sea-eagle is not well known.
This eagle breeds in remote coastal regions along the west Bering Sea and
Sea of Okhotsk in eastern Siberia. Most of the population migrates to Hokkaido,
Japan for the winter. During the breeding season, Steller’s sea-eagles
feed on fish, including salmon, medium to large-sized birds, and mammals.
In winter, fish and carrion are important. Recent reports suggest regional
long-term population declines. Because of its relatively small population
size and restricted breeding area, it is listed as vulnerable by the International
Union for the Conservation of Nature and Natural Resources (IUCN).
In Japan, over-fishing has led wintering eagles on Hokkaido to move inland and scavenge on deer remains left by hunters, exposing them to lead poisoning through ingestion of lead shot. Lead is highly toxic to eagles and a single shotgun pellet can cause death. The use of lead ammunition in hunting was outlawed on Hokkaido in an attempt to reduce lead poisoning and adherence to this ban has meant that this threat has decreased in recent years. As a wide-ranging top predator, the eagles' year-round reliance upon local water quality, fish and sea bird populations, and the degree to which it has been impacted by environmental contaminants suggest that human influences threaten them throughout their range. The Steller’s sea-eagle is useful as a sentinel species for the health of the river and coastal ecosystem it uses, and it is a flagship for regional and global conservation efforts.
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Steller's Sea-eagle Conservation
The San Diego Zoo and Steller's sea-eagle conservation
In 2006, the San Diego Zoo joined forces with Natural Research Ltd. to study the movements of juvenile wild Steller's sea-eagles to help protect this vulnerable species in its native habitat. In 2006, 2007, and 2008, with funding from the San Diego Zoo, Natural Research biologists tagged five nestlings each year in Russia's Magadan State Reserve with satellite transmitters, allowing both researchers and the public to monitor the birds' migration through Google Earth maps.
Unfortunately, all five eagles tagged in 2006 and the five eagles from 2007 have since died or lost their tags. Sadly, due to the location of birds when they stopped transmitting or stopped moving, it is suspected that the majority of the birds died due to human activities. A high mortality rate is expected because in its first year of life, a juvenile eagle will find it difficult to feed itself while undertaking a long migration in the first months after it leaves the nest. However, if the mortality rate is too high to sustain a healthy population, the findings would call for greater conservation of this species.
One bird, eagle No. 65632, survived the longest. It was tagged in the summer of 2006 and it survived two winters and one summer independently, but in October 2008 its transmitter showed the bird had stopped moving. The young bird had flown back and forth between Russia and Japan, passing fishing villages, oil towns, vast forests, and ice. The circumstances of its death are still unknown.
In July 2008, Natural Research biologists tagged five more birds. All five have successfully fledged and have begun their first migration (a new Google map will be in place soon). In 2006 and 2007, most of the birds died soon after leaving the nest, but the 2008 eagles seem to be off to a better start collectively. The first few months will not be easy as the ice becomes thicker and the winter colder.
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Eagle #65630 |
Eagle #65631 |
Eagle #65632 |
Eagle #65633 |
Use the + and - tools on the map to zoom in and out to better see the individual or full paths of the eagles' migration. Click on the markers to see the date that eagle was tracked to that location. Click down and hold when you see the open hand cursor and drag to move around the map. |
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The San Diego Zoo has housed a pair of Steller's sea-eagles since 1996 and has others on loan to four United States zoos as part of continuing efforts to educate the public about this rare species. Natural Research biologists have been studying this bird since 1991.
Large eagles take some years to mature and enter the breeding population. The minimum age at which Steller's sea-eagles become sexually mature is approximately four years. Researchers know next to nothing about this pre-breeding phase of life for this species, or for most eagles, undermining conservation efforts. For this reason, researchers have concentrated their effort on young birds and have used transmitters that are long lived.
Satellite tracking of Steller's sea-eagles
The tagged eagles began their migration in early October from Magadan State Reserve in Russia, and data are being received via the Argos satellite tracking system. Tracking is being done using long-lived battery-powered satellite transmitters. Because the transmitters operate on batteries, their operation is not affected by short days and bad weather in northern latitudes. These transmitters have a predicted four-year lifespan. Tags are fitted using a backpack harness.
Natural Research Ltd. tagged nestlings in 1997, but the transmitters provided only one year's worth of information. This study is expected to provide up to four years of data on migration and mortality rates of juvenile birds, which is more than anyone has obtained to date. It will also provide insight into the ecology of Steller's sea-eagles prior to their entry into the breeding population. Much more than the simple mapping of migration routes, these new data will support long-term conservation of Steller's sea-eagles in the wild.
The importance of eagles
Like the bald eagle for North America, the Steller's sea-eagle is linked intimately with Russia because it breeds there exclusively. In Russia, this species is given full legal protection, but enforcement is difficult in its remote breeding range. The Steller's sea-eagle is offered full protection as a Natural Monument in Japan, where most of the population winters on Hokkaido. The San Diego Zoo is home to a pair of Steller's sea-eagles and has loaned a pair to the Cincinnati Zoo, the Los Angeles Zoo, the Louisville Zoological Garden, and the National Aviary in Pittsburgh. By housing this eagle in a zoological setting, the San Diego Zoo hopes visitors will gain an appreciation for this large raptor and help with the protection of this species. Join researchers by tracking the birds online and see them in person by visiting the Birds of Prey habitat at the San Diego Zoo.
