Thousands of birds are flying overhead right now, migrating south from their breeding areas in Canada. Some might stop over along wooded streams for a few days to replenish their fuel resources, as dozens of small warblers, vireos, and sparrows did last week at our local reservoir. But an even more impressive migration is taking place along the ridge that runs along the western shore of Lake Superior above the city of Duluth MN.
Migrating raptors by the thousands (and some in tens of thousands) are reluctant to cross the expanse of Lake Superior, but they funnel along the ridge line of its western shore, to be counted by volunteer observers of the Hawk Ridge Bird Observatory and photographed by the dozens of bird lovers and photographers who visit daily.
Overcast skies bring the birds down low, closer to observers, which is ideal for photography, but we happened to be there on a sunny afternoon, and the birds were thousands of feet in the air above us.
Broad-winged Hawks are smallish, compact raptors common throughout southern Canada and the eastern U.S. during the summer, but they leave North America during a short span of time in September, largely because they are dependent on the thermals generated by warm air currents rising off the land in the fall. If they wait too long to migrate, warm fall days become unpredictable and so do the thermals they use to gain altitude for migration.
Soaring, instead of flapping flight, is relatively inexpensive for raptors, and by using the thermals to gain altitude to then soar over long distances to the next thermal, they can travel hundreds of miles before running out of fuel stores. For Broad-winged Hawks, the journey from southern Canada to northern South America might be 3-4,000 miles and take them about a month. In optimal conditions, they can travel 300 miles in 6 hours.