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