Driving to a nearby town, today, I saw a curious ballet of sea gulls. A tractor was out in the fields tilling under the last of the fall stubble, and as it moved slowly forward, an undulating wake of white birds followed along after it. There must have been 40 or 50 gulls in the furrows behind the tractor, each leapfrogging over those in front to get to the most newly tilled inches of soil. Altogether, they trailed the tractor for about 20 feet. And as I drove on, I saw other gulls flying purposefully toward that field, ready to join in the dance.