Flights of Fancy
How birds (and bird-watchers) compute the behavior of a flock on the wing
The best computer simulations of bird flocks look wonderfully realistic—Reynolds won an Oscar for some of his flock animations—but do they tell us anything about real birds? Until recently it was hard to answer this question because so little was known about the trajectories of birds in large flocks. There were plenty of films and videos, but tracking individuals in three dimensions was not feasible.
The situation has changed with new data-gathering efforts, the largest being the STARFLAG project, an interdisciplinary collaboration extending across Italy, France, Hungary and the Netherlands. A STARFLAG group at the University of Rome, led by Andrea Cavagna and Giorgio Parisi, has succeeded in tracing the movements of individuals in starling flocks with up to 4,000 members. The Cavagna group did not have to go far to make their observations. Every winter, vast numbers of starlings gather just a few blocks away from the university at the Termini, Rome’s main railway station. Cavagna and his colleagues set up digital cameras on the roof of a nearby building, the Palazzo Massimo.
Because video recorders lack sufficient resolution, the Rome group used cameras meant for still photography and made rapid-fire sequences of exposures. Pairs of cameras were mounted 25 meters apart so that the stereoscopic disparity would provide depth cues, as in binocular vision. Each camera could record five frames per second, which is not quite fast enough for following the movement of starlings. Therefore two pairs of cameras were triggered alternately to give an effective rate of 10 frames per second. Two more cameras (making a total of six) aided in the 3D reconstruction.