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Turkey vulture ‘kettles’ a spectacular fall sight

[123RF.com photo]

It starts in the first half of September. Maybe five or six turkey vultures briefly will share a thermal rising in the bubble of heated air. Until this point in the summer, vultures have been largely solitary foragers.

Such aggregations, large or small, often are referred to as “kettles.” A kettle in late summer may only last a couple of minutes before the birds scatter with each heading off to continue the search for the next dead ground squirrel baking in a pasture.

As September progresses, these kettles become somewhat larger and “stickier.” By “sticky,” I mean kettles persist for longer and longer periods of time before breaking up. The time for migration is near.

Beginning about the third week of September, on some invisible cue, one kettle, then others, begin to set off on migration, each remaining together as they rise up and pass over the Siskiyous into California and points south. At this time, kettles average 20 to 30 individuals.

By the climax of migration late in the first week of October, flocks can be massive. We typically see a few flocks of several hundred birds pass through the valley.

In some years, a flock or two may even exceed a thousand birds. It can cause quite a bit of excitement if the kettle finds itself over your neighborhood as the shadows lengthen and the thermals that carry the birds along on their journey falter. They drop in to fill every tree with roosting birds.

They are quiet guests, but the whitewash can leave a reminder of their visit that lingers for days. Fortunately, they feed little in migration.

I never considered before where these social migrants meet and decide to pool their efforts. So, where is the bus station? By this, I mean where do they come together and form travel groups?

The Swainson’s hawk is another species that migrates in massive flocks. The birds that breed in the semi-arid region of Oregon east of the Cascades head south most often as individuals or maybe small family groups. Satellite tracking has shown many make their way to Texas to feast on grasshoppers meeting up with others that breed in the prairie states before heading out. The bus stop apparently is in Texas.

I learned this fall these grand aggregations of vultures do not occur throughout Oregon. In the central Willamette Valley, I saw no parade of sizable kettles as September progressed. At most, I observed kettles comprising a mere 10 to 15 individuals. If there was a striking climax to vulture migration, I missed it.

Where do our vultures congregate? Vultures breed as far north as southern British Columbia. The northern populations are not particularly abundant, and it makes sense that migrant flocks start off throughout their range as kettles of modest size.

But somewhere these flocks tend to assemble into the large groups that pass through the Rogue Valley. Having seen the number of vultures that summer in the Roseburg area, I suspect a major assembly area is in the Umpqua Valley.

In future years, I encourage you to watch for and enjoy the fall vulture spectacular in the Rogue Valley, one not accessible to many Oregonians.

Stewart Janes is a retired biology professor at Southern Oregon University. He can be reached at janes@sou.edu.