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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Read the latest blog from a Steller's sea eagle researcher...
Steller's Sea Eagle Conservation
Protecting a species
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. With funding from the San Diego Zoo, Natural Research biologists tagged five nestlings 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, four of the five eagles have either died, lost their tags, or the tags failed. Sadly, it is suspected that the birds died. A high mortality rate in an eagle’s first year of life can be expected because it is hard for juvenile eagles to feed themselves and undertake a long migration in the first months after leaving 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. Natural Research biologists and the San Diego Zoo curator of birds will return to Russia in July 2007 to tag five more nestlings to continue data collection of this important phase of life.
One bird, eagle No. 65632, did survive the winter (see the Google map below). Around New Year's Day, this eagle crossed into Japan and then moved onto the islands of Rishiri-to and Rebun-to, which lie west of the most northerly tip of Hokkaido. There it spent its first winter. In early April, it headed back north onto southern Sakhalin and in late April started to push slowly north. By the end of May 2007, it had reached a location south of the town of Katangli near Nogliki on the eastern seaboard of Sakhalin. Nogliki and Katangli are oil towns. Most recently this bird may have moved out onto a boat or other man-made structure in the sea because the satellite location suggests that it has been sitting some small distance from the shore.
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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 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 about 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 that provide less accurate locations, but because they 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. One bird was tagged with a solar-powered GPS (Global Positioning System) transmitter that gives highly accurate locations uploaded by satellite every few days over a period of about three years. The GPS tag is an experiment to determine if it is feasible to use in the future and is providing useful data for this project. 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.
