How Al­berta bird­ers-turned-cit­i­zen sci­en­tists dis­cov­ered a golden ea­gle mi­gra­tion route through the Rock­ies

Canadian Geographic - - CONTENTS - By Sarah He­witt Read an ex­tended ver­sion of this story, in­clud­ing more on how Peter Sher­ring­ton’s data is help­ing con­serve golden ea­gles, at can­­gles.

How Al­berta bird­ers dis­cov­ered a golden ea­gle mi­gra­tion in the Rock­ies

ON A BRIGHT DAY in early spring, a group of cit­i­zen sci­en­tists stands in a for­est clear­ing off the Hay Meadow trail in the front range of the Rocky Moun­tains, about 75 kilo­me­tres west of Cal­gary, binoc­u­lars trained sky­ward. They’re scan­ning for golden ea­gles, one of the largest rap­tors in North Amer­ica. Be­fore long, a speck ap­pears above an un­named peak. It catches a ther­mal, cir­cles high and soars over­head as the peo­ple be­low strain to glimpse the band of white across the tail base that dif­fer­en­ti­ates a ju­ve­nile from an adult. In the spring and fall, hun­dreds of golden ea­gles stream along the Rock­ies’ east­ern ridges on an aerial high­way that stretches from Alaska to Mex­ico. In the Cree lu­nar cal­en­dar, Fe­bru­ary is known as Ea­gle Moon, yet sci­en­tists didn’t know this Alaska-yukon pop­u­la­tion of the birds mi­grated at all un­til rel­a­tively re­cently. “It all hap­pened quite ac­ci­den­tally,” says Peter Sher­ring­ton, an avid birder who for more than two decades has spear­headed a vol­un­teer ef­fort to track the ea­gles’ mi­gra­tion. One March morn­ing in 1992 in Kananaskis Coun­try, Sher­ring­ton was watch­ing a pine gros­beak when he saw a golden ea­gle. Min­utes later, two more ea­gles flew past. By day’s end, he’d counted 103 ea­gles, and over the next four days, the count would rise to 400. Golden ea­gles are ter­ri­to­rial and have home ranges that can cover as much as 200 square kilo­me­tres. They’re found through­out the North­ern Hemi­sphere, and the ma­jor­ity of pop­u­la­tions stud­ied in Fin­land and Rus­sia ap­pear to be ei­ther year-round res­i­dents in their habi­tat or par­tial mi­grants, meaning only the ju­ve­nile birds travel far afield. The same was thought about the Alaska-yukon pop­u­la­tion. No one sus­pected they were watch­ing the largest golden ea­gle mi­gra­tion on the planet. “When you see some­thing that doesn’t fit with the known data, you as­sume it’s anoma­lous, but maybe it’s our knowl­edge that’s wrong,” Sher­ring­ton says. In the fall of 1992, he be­gan count­ing ea­gles in earnest, leav­ing his oil-in­dus­try job to start the non-profit Rocky Moun­tain Ea­gle Re­search Foun­da­tion. To date, thou­sands of vol­un­teers have logged more than 30,000 hours in the field, and recorded sight­ings of more than 24,000 golden ea­gles. They’ve been able to iden­tify not only the mi­gra­tion route along the Rocky Moun­tain front, but also, work­ing with re­searchers in Alaska and Mon­tana, a se­condary mi­gra­tion cor­ri­dor far­ther west through the Rocky Moun­tain trench. “This whole thing is just the re­sult of me say­ing ‘This is in­ter­est­ing, I won­der what’s hap­pen­ing here,’ and then pur­su­ing it,” Sher­ring­ton says of his cit­i­zen science ex­pe­ri­ence. “It’s a case of look­ing up and won­der­ing what’s out there.”

A re­searcher at Rap­tor View Re­search In­sti­tute in Mon­tana re­leases a wing­tagged golden ea­gle. The tags help spot­ters eas­ily iden­tify mi­grat­ing birds.

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