Raptor Initiative: Fall Migration Studies
The annual, 7,800-mile journey of Swainson’s Hawks is regarded as one of the planet’s most amazing wildlife migrations. However, little is known about the route they take from nesting habitat in southern Canada and the Rocky Mountains, to lush Patagonian grasslands in Argentina. In 2010, our research team working in Yellowstone followed a hunch that Swainson’s Hawks and other raptor species migrate right through the park’s Hayden Valley. Our subsequent field work and observations through the Yellowstone Raptor Initiative have revealed a higher number, and greater diversity, of raptors in Yellowstone than had ever been documented or even suspected.
Field Location: North Hayden Valley, Yellowstone National Park
David Haines: “Bird!” Coops, coming across from the bump to the right.
Jeep Pagel: Subadult?
David Haines: Adult.
Leslie Henry: Moving past the grey puffy cloud, circling right?
David Haines: No, that is a different bird; mine is just at treeline, moving fast….
Jeep Pagel: Did you see the Swainson’s bopping behind it?
Leslie Henry: No, do you have it?
David Haines: Mine’s gone; mark it; I have to see if that other bird was a Ferrug. There was another male k-bird near the Swainson’s; Leslie, you got it?
Leslie Henry: Yes, I see the kestrel; the Swainson’s is a U Dark, with a U Light behind it near Washburn, moving towards the roadcut.
If you are fluent in raptor-migration parlance, you may have already translated this short snippit of conversation. You might discern the field crew saw Cooper's Hawk, Swainson’s Hawk, Ferruginous Hawk and American Kestrel in short succession. But without being present, you might miss the inflection and tone, and the overall excitement each raptor brings to the observers. (Read full translation here>> )
The above conversation -- and other similar exchanges -- happened almost every day during September and into October 2011 as we monitored the fall raptor migration. Raptors are birds of prey; anything from the diminutive -- but fierce -- American Kestrel, to the hefty and distinctive Ferruginous Hawk, to the larger Golden Eagle; and include almost a score of other raptors in between.
Our base was an observation point in northern Hayden Valley, out of sight of the public. During our fall studies, these dialogues began in the mid-morning, and increased as scores of raptors roused from their nighttime roosts to take advantage of any rising air columns and lift created by the wind.
The days are long at the observation point. Because migrating raptors fly so high, many appear as an eye-straining speck in the distant sky. By the end of the day, our eyes burn from almost constant viewing through high-power binoculars and spotting scopes. Upon close examination through our lenses, we identify raptor gender, age class, and other characteristics.
We think that this migration is not new, though it has never been officially documented. Unknown to park visitors and staff, raptors have probably passed through Hayden Valley annually for millennia. The annual movement of thousands of raptors through the Yellowstone River Corridor is one of those increasingly rare “discoveries” which helps scientists and visitors marvel at the complexity and global importance of Yellowstone National Park.
We have also confirmed a resident population of Swainson’s Hawks that nest and raise their young in Yellowstone. After migration to a safe wintering spot far south of Yellowstone, these and other raptors species will build up fat reserves and fitness to prepare them for the following spring return to breeding habitat in or near the Yellowstone ecosystem. Here they will defend their past year’s territory, show off their hunting and flying skills during courtship. They will hopefully breed and lay a clutch of eggs, which they will incubate for a month or more. If all goes well, the eggs will hatch, the young will fledge and learn to hunt, eventually disperse, and repeat the cycle of life via the annual fall migration through North Hayden Valley.
As field going biologists and ecologists who staff the observation post each day, we consider ourselves to be extremely fortunate to observe the raptors that use the Yellowstone River corridor as their migration pathway. We have realized that we are not merely counting individual raptors in the sky; we are witnessing a migration phenomenon and important ecological cycle in North America.
Because no one had collectively studied Yellowstone National Park’s raptors, the Yellowstone Raptor Initiative (YRI) was created. It is a research and education program to monitor raptors, evaluate their ecological contribution to the ecosystem, and provide experiential learning opportunities for park visitors.
Supported by a modest grant, YRI staff implemented pilot fieldwork in 2009 to ascertain the need and potential for such a project. In 2011, YRI received an $85,000 grant from the Yellowstone Park Foundation that has helped us develop a small but professional, seasonal monitoring project.
Dr. Douglas Smith is a co-founder and the project leader of the YRI, in addition to his role as Yellowstone’s Wolf Project Leader. Katy Duffy, also a co-founder, is a ranger with the park's Division of Interpretation, with a special emphasis on raptor education. I am a raptor ecologist who works for the U.S. Fish and Wildlife Service, and have been fortunate to assist the YRI since its inception as a co-founder. Since 2009, I have helped YRI find numerous raptor nests, and have entered Peregrine Falcon and Golden Eagle nest sites in Yellowstone to collect eggshell fragments and prey remains.
Through our careful data collection, with the help of seasonal researchers, we are contributing to the mounting scientific interest in the biological difficulties and ecological complexities which raptors face as they pass through human-dominated landscapes.
The Yellowstone Raptor Initiative is supported, in part, by a contribution from the Hawk Migration Association of North America to the Yellowstone Park Foundation.