Date: 9/13/18 8:34 am
From: bob augustine <augustinebob8...>
Subject: [MDBirding] Broad-wings Coming
September is the month when we anticipate the migration of thousands of Broad-winged Hawks, mostly from Canada, through our region on their way to Bolivia and points south. We hope that we will be able to witness the spectacle of the peak flight that usually occurs around the 18th. It used to be earlier, but global warming has moved it later. Small numbers of other hawks, falcons, Ospreys, and eagles will join with them.

We can experience this flight in two main ways. If there is sunny weather, the hawks will move into the coastal plain where they can use thermals and pass over us at about 3,000 feet. They are just dots, barely visible to the naked eye, but if there are nice, big, puffy cumulus clouds you may see large, swirling flocks (called "kettles" because they resemble the swirling air bubbles in a boiling kettle) against them anywhere in our region, which is quite a sight, but only with binoculars.

If there is no sun, the Broad-wings cannot use their preferred method for
migrating. They will move to the mountains and follow ridges sw--on a heading of 242 degrees, generally at lower altitudes, toward Corpus Christi, Texas and the eastern slope of Mexico. That's the time to go to the hawkwatches, which are mostly on ridges. There you will see flocks arise in the ne and cross the ridge to the sw. This pattern is unique to Broad-wings. Other hawks just follow ridges.

Rarely, inclement weather will approach from the west and trap birds up against the Chesapeake Bay and a low-altitude, forced flight will be concentrated through Montgomery County, but it has proven impossible to determine exactly where. A couple of years ago a flight at Cromwell Valley Park, n of Baltimore, crossed Montgomery County near Darnestown 2 hours later. Other flights have crossed near Great Falls. The last couple of years have had sunny conditions and the flight passed high over us largely undetected.

Bad weather next week could divert the entire flight to the west.

Bob Augustine
Rockville, MD
13 Sept. 2018

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