  Aerial displays of starlings (Sturnus vulgaris) at their communal roosts are
complex: thousands of individuals form multiple flocks which are continually
changing shape and density, while splitting and merging. To understand these
complex displays both empirical data and models are needed. Whereas detailed
empirical data were recently collected through video recordings and position
measurements by stereo photography of flocks of thousands of starlings, there
are as yet no models that generate these complex patterns. Numerous computer
models in biology, however, suggest that patterns of single groups of moving
animals may emerge by self-organisation from movement and local coordination
(through attraction, alignment and avoidance of collision). In this paper, we
investigated whether this approach can be extended to generate patterns
resembling these aerial displays of starlings. We show in a model that to
generate many of the patterns measured empirically in real starlings we have to
extend the usual rules of local coordination with specifics of starling
behaviour, mainly 1) their aerial locomotion, 2) a low and constant number of
interaction-partners and 3) preferential movement above a roosting area. Our
model can be used as a tool for the study of these displays, because it
provides new integrative hypotheses about the mechanisms underlying these
displays and of swarming patterns in biological systems in general.
