The annual migration of huge black birds

Jon Hammond.

Late afternoon sunlight illuminates a Turkey Vulture's wings as it prepares to land.

Summer has faded and autumn has returned to the Tehachapi Valley, bringing with it the annual spectacle of thousands upon thousands of migrating Turkey Vultures.

Day after day, these big black birds soar through Tehachapi Pass on their journey southward. The vultures hitch rides on thermals to gain elevation, circling as they ascend rising columns of warm air like an invisible spiral staircase.

This flight behavior is known as "kettling," for the way the jumbled circling birds look as though they were being stirred inside an enormous glass kettle. The sight of kettling turkey vultures, in flocks ranging from a few dozen individuals to many hundreds of soaring birds, is a familiar one to anyone raised in the Tehachapi area.

I haven't noticed as many Turkey Vulture kettles this year as I sometimes do, but that's probably just a matter of timing, since they've definitely been coming through in large numbers.

Not all the local encounters are from a distance: birds who are still over the valley in late afternoon, when temperatures are dropping and air is falling rather than rising, must spend the night in the hospitality of Tehachapi's trees.

Throughout the area there are locations where migrating Turkey Vultures (Cathartes aura) tend to roost overnight year after year. They typically select large, mature trees and they are fond of roosting in snags, which are large standing dead trees. Migrating Turkey Vultures have often roosted overnight at Philip Marx Central Park, in large trees along Old Town Road, and many other locations.

Most birds prefer a more sheltered night roost, but vultures are so large that they basically have no predators so concealment isn't a requirement. And as graceful as they are in the air, vultures are ungainly when earthbound and a bare tree is easier for them both to land on and later exit.

Despite their large size, the Turkey Vulture migration is almost entirely a visual event because these birds are essentially silent. They tip and circle and soar noiselessly as they fly like huge untethered kites.

The only noise they make is when they land for the night, which can be a chaotic event for a flock of migrating vultures. Their landing can be a little awkward, and they semi-crash land onto limbs at times. Near dusk you can hear the sounds of vultures colliding with branches as well as the earlier arrivals hissing in irritation at the later birds who may bump into or jostle them.

Once they settle in for the night, they remain on their perches until midmorning when the warming sun starts the air moving upward. Then the vultures take wing like feathered sailplanes and start looking for thermals to help them circle upwards.

Turkey Vultures don't migrate in search of a food source like most birds, because the mortuary business they're in is steady, in good times or bad, summer or winter. The dead animals that they consume – typically mammals – succumb year-round.

Instead, vultures follow the sun south, because their flight engines are mostly solar powered – they depend on the sun to warm air up enough to give vultures the lift they need to reach adequate elevations from which to scan the landscape for deceased animals.

Jon Hammond.

A Turkey Vulture in the foreground and a Common Raven behind shows the size difference between these two large dark birds.

As a result, the vulture populations of Canada, Washington, Oregon and Northern California head south down the Great Central Valley. The Sierra Nevada range forms a barrier to the east until they soar their way south to two gateways through the mountains: Walker Pass and Tehachapi Pass.

Scientific counts conducted by birders in the South Fork of the Kern River Valley and in Tehachapi Valley by the Tehachapi Mountains Birding Club have recorded more than 30,000 Turkey Vultures passing annually through each of these two locations.

If you live in Tehachapi long enough this yearly phenomenon seems ordinary, and it's easy to assume that the same thing happens everywhere, but it does not. We happen to be a vital part of an ancient migration route that may well precede the arrival of the first people here more than 10,000 years ago.

So look to the skies on warm cloudless Tehachapi days for the next several weeks, and you may see part of the river of birds that flows through here every autumn enroute to Southern California and Mexico.

Keep enjoying the beauty of life in the Tehachapi Mountains.

Jon Hammond is a fourth generation Kern County resident who has photographed and written about the Tehachapi Mountains for 38 years. He lives on a farm his family started in 1921, and is a speaker of Nuwä, the Tehachapi Indian language. He can be reached at [email protected].