The days of turkey vultures patrolling the skies, rocking back and forth on the gentle summer breezes, are just about over for the year. In a period of about three weeks beginning around the last week of September, the skies will empty out in spectacular fashion as vultures head for their winter vacation in southern California and northern Mexico.
Vultures and condors of the New World — meaning North and South America — are a weird group of birds. Unlike vultures of the Old World — those in Africa and Asia, which everyone agrees are closely related to eagles — New World vultures are an ornithological puzzle. They just don't fit in.
For many years, our vultures were considered birds of prey gone soft. However, a small group of researchers complained that the proteins of vultures differed from hawks and eagles, and other anatomical features just weren't right.
DNA studies seemed to settle the issue, and they were declared really strange storks. New field guides and checklists were written that placed vultures alongside herons, ibises and storks.
Well, no case is ever closed in science. New data can always cause old ideas to be reexamined, and the most recent DNA data placed our vultures back with the hawks and eagles. Stay tuned. I'm sure there will be much more to this story.
In the meantime, summer is moving toward fall and vultures are following the sun. For many birds, migration is a lonely venture. Flycatchers, warblers and others set out solo as the light fades from the sky on an autumn night, hoping to make it 100 miles or more before morning. After a brief layover, they repeat the process and keep going until they arrive at their winter destination.
Not so turkey vultures, which gather into flocks ranging in size from a dozen to more than 500. Flocks of 30 to 50 birds are most common.
When migrating, vultures seek out thermals, bubbles of warm, moist air that rises slowly from the surface on calm, sunny days. Within a thermal, air circulates in a pattern resembling a large donut lying flat. Air rises through the center and falls on the outside.
Vultures know (and so do hawks, gulls and glider pilots) that if they find a thermal and circle within it, they'll get a free ride in an elevator.
A flock of vultures circling within a thermal is called a "kettle." A kettle will ride the thermal high until it begins to falter, then peel off south seeking the next thermal.
Thermals form over hills and other high points, making their locations somewhat predictable. In this way vultures can travel great distances without ever having to flap.
When the sun begins to settle toward the horizon, the energy to power thermals fades, and the vultures must come to earth.
There are several traditional roosts for turkey vultures in the Rogue Valley. One is along I-5 just south of the new Sports Park. Another is along the Bear Creek Greenway at the south end of Talent. However, almost any grove of trees may become a roost for a night.
Over the next few weeks, check out the skies and maybe you will be lucky enough to spot kettles of vultures heading south. You might even have one visit for the night.
Stewart Janes is a biology professor at Southern Oregon University. Reach him at firstname.lastname@example.org.