The immature Bearded Vultures at Giant's Castle often indulge in aerial acrobatics. I'm not sure what it means, but it seems to have a hierarchical function - they try to dominate each other, sometimes even resulting in brief claw locking and spiralling. These two did not go to that extreme, but the one at the back (the older bird) constantly shadowed the younger one, preventing it from landing and feeding.
Camera Model: Canon EOS-1D Mark III
Date/Time: 2008:05:07 10:18:04
Shutter speed: 1/2000 sec
Aperture: 7.1
Exposure mode: Av
Flash: Off
Metering mode: Multi-segment
ISO: 400
Focal length: 500mm
Nice work getting two similar positions on the wings and the eyes are electric. BG complements them well and appears to be mountains giving a hint of their environment.