Whereas contrails are largely the result of water vapor freezing and condensing, these streaks are different. In short, the vortices you see (or may see as swirling air behind an approaching aircraft) are generated from pressure differentials from above and below the wings, and are associated with a certain kind of turbulence aircraft (particularly larger ones) create — called "wake turbulence."
In this crazy aviation video, you can witness the result first hand. As you'll see, from the right angle, the effect is stunning. The vortices look like brushstrokes in the sky. In this particular example, we see an Emirates 777 landing in Birmingham, England (BHX). Along with the vortices behind the wings, notice them over the wings during the flare, right before touch down. Some conspiracists will argue that these vortices are chem trails, employed by the government to turn us into mindless zombies... I'd respectfully disagree with them. Whoever you believe, I think we can all appreciate their beauty.
