In recent weeks, Minnesota temperatures have dropped into the thirties, forcing Carleton students to unpack their fleece coats and sending raptors (think hawks, not Jurassic Park) on their annual migration southward.
Raptor migration patterns are dictated by topography and the presence of bodies of water. In order to conserve energy, raptors use rising air to gain elevation and then glide horizontally. Specifically, they use thermal currents, columns of warm air, and updraft currents, air deflected upwards as it reaches mountains. Because these thermal currents are weaker above water than above land, raptors are concentrated along the edges of the Great Lakes, making Duluth a center for raptor migration.
The Hawk Ridge Bird Observatory in Duluth, Minnesota contributes to raptor research and tracking efforts. Thus far in the fall season they have reported 58,666 raptors, including thousands of Bald Eagles, Sharp-shinned Hawks, and Broad-winged Hawks. Last week, a group of Carleton students visited this watching station in Duluth to experience the migration first hand.
They witnessed only a glimpse of the migration, because the species composition will change in the coming months. The timing and distance of migrations are species-specific. The fall migration season begins with Sharp-Shinned Hawks and Ospreys in September and goes until November when various eagles and Red Tailed Hawks fly south.
While some raptors make it as far as the Argentinian Pampas, others remain in Northfield over the winter. Bald Eagles, for example, winter within a huge geographic range, from southern Minnesota to Florida, seeking out areas with open water to fish in, such as the Cannon River. Red-tailed Hawks are also able to winter in the Arb, but they are dependent on terrestrial food sources like snakes, rabbits, insects, and birds. In addition to common sightings of Bald Eagles and Red-tailed Hawks, Sharp-Shinned Hawks are occasionally spotted in the Arb during winter months. As the crisp fall turns into winter, winds are propelling an intercontinental migration and bringing raptors into our own backyard.