The Weather Notebook: Hawks

Hawks
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Hi, I'm Dave Thurlow. I recently had a conversation with author Scott Weidensaul about birds, migration and weather. He's the author of a book called "Living on the Wind."

Coopers Hawk

DT: "Now, we know that this time of year we expect song birds, small birds to migrate, but this is also a time to watch large number of hawks migrate and they certainly use the weather in very specific ways. What are some of those."

SW: "Well, here in eastern Pennsylvania where I live, the hawks are moving down the ridges of the Appalachians and you see the same phenomenon in the Rockies and other parts of the US. And the birds here are using deflection currents. They're picking days when there's a strong northwest wind, again after the passage of a cold front when you've got a rising barometric pressure and fresh winds. And these winds strike these ridges roughly at 90 degrees and they bounce up. They form this pillow of rising air on the upwind side of the ridge. And what these hawks are able to do is essentially surf all the way down for hundreds of miles along these ridges with little or no energy output. I mean, all they have to do is set their wings and glide. It's a remarkable thing to watch. And it looks like it would be so much fun.

I know some of the glider pilots get a kick out of doing that kind of dynamic soaring as well. But the hawks have been doing it for hundreds of thousands, if not millions of years.

Now, on the days when the wind starts to falter, then they'll switch tactics. They'll look for places where there's an active thermal air current, where there's a rising bubble of hot air, perhaps rising up over a parking lot. We're finding now that some hawks have switched to a more metropolitan corridor migration route, because they're going from megalopolis to megalopolis following the rising bubbles of air over parking lots and shopping malls and things like that."

The Weather Notebook is a production of the Mount Washington Observatory.