Where Montana's Rocky Mountains spill down to the Great Plains, hundreds of migrating golden eagles, bald eagles, and hawks pass overhead each February and March, riding air currents created by west winds cresting the mountains as they travel from Mexico to Alberta, Canada. On a nearby hill, a pair of researchers count eagles and hawks all day long each spring, and on one day they counted 230 golden eagles, a record sighting in the United States. Hawkwatch International and the U.S. Forest Service monitor this and other migration sites, using changes in eagle and hawk numbers to help measure ecosystem health and set conservation priorities.