Colby Biologists Weigh In on Steller’s Sea-Eagle Sighting

Natural Sciences5 MIN READ

Experts and students shed light on the eagle’s unusual residency in Maine

By Linzy Rosen '22Photography by Louis Bevier
February 15, 2022

For years, the Steller’s sea-eagle had never been observed in the Lower 48. Recently, one wayward eagle settled around Five Islands off Georgetown in midcoast Maine, and Colby biologists were among the front-line scientists observing, studying, and tracking the majestic, rare arctic bird.

“It was kind of a mad rush to see the bird,” said Louis Bevier, a longtime research associate at Colby who co-teaches ornithology with his wife, Professor of Biology Cathy Bevier, and serves as chair of the Maine Bird Records Committee. “It’s such a fabulous-looking thing.” 

The eagle’s unexpected journey has upended schedules, heightened enthusiasm, and piqued the curiosity of serious scientists and Sunday birders alike, who have flocked by the hundreds to tiny points of land from Georgetown to Boothbay Harbor in hopes of spotting the eagle. 

Characterized by its large bright-orange beak, white leading edge to its wings, and an eight-foot wingspan, the Steller’s sea-eagle is among the world’s largest raptors, weighing up to 20 pounds.

The eagle’s arrival in Maine has been likened to an exotic mystery. The Beviers and their Colby colleagues are helping to unravel the enigma with their observations and are sharing their insights with the larger birding community.

Scientists consider this wandering Steller’s sea-eagle—one of an estimated 5,000 left in the world and currently listed as vulnerable by the International Union for Conservation of Nature’s Red List of Threatened Species—to be a “vagrant.” This is when an animal strays far beyond its natural range for an unspecified period of time. Vagrancy is always a possibility for birds, and such an occurrence would likely not typically make headlines, said Chris Moore, assistant professor of biology, who has seen the eagle in Georgetown.

But an eagle of this size and stature so far out of its normal range has caused a stir, he said. “It happens to be very charismatic,” Moore said. “It’s a large, beautiful bird.”

The Steller’s sea-eagle near Boothbay, Maine. Part of the bird’s distinguishing features is the white leading edge to its wings.

Louis Bevier and other observers have helped document the eagle’s whereabouts and confirmed that it’s the same individual eagle that has been sighted across North America for a year or more. The eagle’s feather markings “are almost like fingerprints,” he said, enabling scientists to track its cross-continent journey and observe its behavior. 

Native to the eastern coast of Russia and wintering in Japan, occasionally as far south as Korea, this vagrant raptor is suspected to have been roaming since mid-2020. This singular Steller’s sea-eagle was identified on Alaska’s Denali highway in August 2020, and the same eagle was identified again in July 2021 in Qu​​ébec and New Brunswick, Canada. The lone eagle reappeared in Nova Scotia in November 2021, then briefly wowed crowds in Massachusetts in December. 

But it didn’t stay in Massachusetts long, said Cathy Bevier who along with her husband joined many Colby faculty and others observing the eagle when it landed in Georgetown before New Year’s. 

High-quality photographs have helped identify similarities in molt patterns that can vary between individual birds. Many observers have pointed out a distinctive white spot on this eagle’s left wing, which is an older feather that’s lingered. Incoming feathers are darker and fresher, whereas older feathers are paler. There’s also a distinctive break in one of the bird’s primary feathers— the biggest flight feathers—likely the result of catching the feather on a branch.

Because the bird will hold its feathers for more than a year before it molts, Louis Bevier said, these patterns likely will continue to be a valuable tool for identification. Evaluating observational data has been pivotal in tracking the Steller’s sea-eagle, but “it’s kind of an under-appreciated aspect of science,” he said.

As biologists study the eagle, they also are interested in the role of climate change in its journey, and whether such off-course ventures may become the norm going forward. Variations in temperature, precipitation, or climatic conditions can influence the vagrancy of the Steller’s sea-eagle. Increased storms with higher rainfall in Northeast Asia could be making it harder for these birds to fish in flooded rivers, Louis Bevier said. This could help to explain the solo mission. 

Human disturbance and climate change are other potential reasons for this eagle’s vagrancy, he said. There’s a good chance that the eagle could find suitable habitat in Maine, he added, given similarities in weather, its usual habitat, the availability of food, and resources.

With its eight-foot wingspan, the Steller’s sea-eagle, seen here soaring above Southport, Maine, is among the largest raptors in the world.

Scientists aren’t the only ones gawking. The eagle has energized numerous online groups for birders, where Colby students are in on the conversation. 

“I’m getting messages every 10 minutes,” said John Shamgochian ’21, who ventured to Georgetown along with several other Colbians in late December, after Iz Varghese ’22 organized the trip. “It’s been a huge boost for birding in Maine, and it’s drawing so many birders from outside of the state.” 

These birders play key roles in data collection. Dedicated observers, sometimes referred to as citizen scientists, have tracked the bird’s daily flight patterns. Though the eagle could fly away at any point, “there’s a predictable pattern, at least in this small corner where it’s been,” said Cathy Bevier.

These closely tracked patterns could help scientists understand whether the eagle’s behaviors have remained typical as it explores new terrain. “Sometimes animals do have very predictable feeding patterns, called traplining,” she continued. Some of the most well-documented instances of traplining are among hummingbirds and bees. They move from flower to flower in a predictable way and follow patterns based on their resources.

Collecting data on the Steller’s sea-eagle will continue to further scientists’ understanding of the bird and vagrancy as a whole, she said.