This is Bird Note.

The sight of hundreds of vultures slowly circling overhead might seem pretty ominous,

but most of the time, it just means the vultures are on their way somewhere else.

In the daytime, hot air rises as the sun heats the ground.

The rising column of air is called a thermal, and it's the perfect way for a turkey vulture

to hitch a ride.

Like an elevator to the skies, the thermal gently wafts the vultures upward.

They move in a slowly ascending spiral around the thermal, rarely flapping and instead coasting

on the breeze. When many vultures ride the same thermal, it's called a kettle. During raptor

migration, kettles can swell with many different raptor species, like this Swainson's hawk.

Hawks see the swirling vultures and join in, taking the opportunity to save their energy.

The air current lifts the birds hundreds or thousands of feet in the air before petering out.

Finally, the raptors leave the thermal and glide downward for miles,

often far enough to take them to another thermal.

Thermals make raptor migration a breeze and a spectacle for observers on the ground.

For Bird Note, I'm Michael Stein.

Support for Bird Note is provided by Jim and Beer to Faulkner and generous listeners around the world.