  The most startling examples of collective animal behaviour are provided by
very large and cohesive groups moving in three dimensions. Paradigmatic
examples are bird flocks, fish schools and insect swarms. However, because of
the sheer technical difficulty of obtaining 3D data, empirical studies
conducted to date have only considered loose groups of a few tens of animals.
Moreover, these studies were very seldom conducted in the field. Recently the
STARFLAG project achieved the 3D reconstruction of thousands of birds under
field conditions, thus opening the way to a new generation of quantitative
studies of collective animal behaviour. Here, we review the main technical
problems in 3D data collection of large animal groups and we outline some of
the methodological solutions adopted by the STARFLAG project. In particular, we
explain how to solve the stereoscopic correspondence - or matching - problem,
which was the major bottleneck of all 3D studies in the past.

Quantitative Methods;Statistical Mechanics;Populations and Evolution