Bird flocking is a striking example of collective animal behaviour. A vivid illustration of this phenomenon is provided by the aerial display of vast flocks of starlings gathering at dusk over the roost and swirling with extraordinary spatial coherence. Both the evolutionary justification and the mechanistic laws of flocking are poorly understood, arguably because of a lack of data on large flocks. Here, we report a quantitative study of aerial display. We measured the individual three-dimensional positions in compact flocks of up to 2700 birds. We investigated the main features of the flock as a whole - shape, movement, density and structure - and discuss these as emergent attributes of the grouping phenomenon. We find that flocks are relatively thin, with variable sizes, but constant proportions. They tend to slide parallel to the ground and, during turns, their orientation changes with respect to the direction of motion. Individual birds keep a minimum distance from each other that is comparable to their wingspan. The density within the aggregations is non-homogeneous, as birds are packed more tightly at the border compared to the centre of the flock. These results constitute the first set of large-scale data on three-dimensional animal aggregations. Current models and theories of collective animal behaviour can now be tested against these results.
Deep Dive into An empirical study of large, naturally occurring starling flocks: a benchmark in collective animal behaviour.
Bird flocking is a striking example of collective animal behaviour. A vivid illustration of this phenomenon is provided by the aerial display of vast flocks of starlings gathering at dusk over the roost and swirling with extraordinary spatial coherence. Both the evolutionary justification and the mechanistic laws of flocking are poorly understood, arguably because of a lack of data on large flocks. Here, we report a quantitative study of aerial display. We measured the individual three-dimensional positions in compact flocks of up to 2700 birds. We investigated the main features of the flock as a whole - shape, movement, density and structure - and discuss these as emergent attributes of the grouping phenomenon. We find that flocks are relatively thin, with variable sizes, but constant proportions. They tend to slide parallel to the ground and, during turns, their orientation changes with respect to the direction of motion. Individual birds keep a minimum distance from each other that
1
An empirical study of large, naturally occurring
starling flocks: a benchmark in collective animal
behaviour
MICHELE BALLERINI1,2, NICOLA CABIBBO3,4, RAPHAEL CANDELIER3,
ANDREA CAVAGNA1,5, EVARISTO CISBANI2, IRENE GIARDINA1,5, ALBERTO
ORLANDI1, GIORGIO PARISI1,3, ANDREA PROCACCINI1,3, MASSIMILIANO
VIALE3 & VLADIMIR ZDRAVKOVIC1
1Centre for Statistical Mechanics and Complexity (SMC), CNR-INFM; 2Istituto
Superiore di Sanita’(ISS); 3 Dipartimento di Fisica, Universita’ di Roma ‘La Sapienza’;
4Istituto Nazionale di Fisica Nucleare, 5Istituto dei Sistemi Complessi (ISC), CNR;
Correspondence to:
Irene Giardina
SMC, CNR-INFM, Dipartimento di Fisica, Universita’ di Roma ‘La Sapienza’,
P.le Aldo Moro 2, 00185 Roma, Italy
irene.giardina@roma1.infn.it
2
M. Ballerini, A. Cavagna, A. Orlandi, A. Procaccini, V. Zdravkovic:
SMC, CNR-INFM, Dipartimento di Fisica, Universita’ di Roma ‘La Sapienza’,
P.le Aldo Moro 2, 00185 Roma, Italy
N. Cabibbo, G. Parisi:
Dipartimento di Fisica, Universita’ di Roma ‘La Sapienza’, P.le Aldo Moro 2,
00185 Roma, Italy
E. Cisbani:
ISS, viale Regina Elena 299, 00161 Roma, Italy
M. Viale (current address):
Dipartimento di Fisica, Universita’ di Roma 3, via della Vasca Navale 84, 00146
Roma, Italy
R. Candelier (current address):
GIT / SPEC / DRECAM, Bat. 772, Orme des Merisiers, CEA Saclay, 91191 Gif
sur Yvette, France
3
Abstract:
Bird flocking is a striking example of collective animal behaviour. A vivid
illustration of this phenomenon is provided by the aerial display of vast flocks of
starlings gathering at dusk over the roost and swirling with extraordinary spatial
coherence. Both the evolutionary justification and the mechanistic laws of flocking are
poorly understood, arguably because of a lack of data on large flocks. Here, we report a
quantitative study of aerial display. We measured the individual three-dimensional
positions in compact flocks of up to 2700 birds. We investigated the main features of
the flock as a whole - shape, movement, density and structure - and discuss these as
emergent attributes of the grouping phenomenon. We find that flocks are relatively thin,
with variable sizes, but constant proportions. They tend to slide parallel to the ground
and, during turns, their orientation changes with respect to the direction of motion.
Individual birds keep a minimum distance from each other that is comparable to their
wingspan. The density within the aggregations is non-homogeneous, as birds are packed
more tightly at the border compared to the centre of the flock. These results constitute
the first set of large-scale data on three-dimensional animal aggregations. Current
models and theories of collective animal behaviour can now be tested against these
results.
Keywords: collective behaviour; flocking; Sturnus vulgaris; emergent properties.
4
The aerial display of large flocks of birds is a stunning example of collective
behaviour in animal aggregations (Emlen 1952). A paradigmatic case is provided by
European starlings (Sturnus vulgaris) (Feare 1984). These birds can be observed in
many cities, where they establish their roosting sites. Shortly before sunset starlings
return to their roost and, prior to retiring for the night, they form sharp-bordered flocks,
ranging from a few hundred to tens of thousands of birds, which wheel and turn over the
roosting site until darkness falls. Flocks exhibit strong spatial coherence and are capable
of very fast, highly synchronized manoeuvres, either spontaneously, or as a response to
predator attacks. Many features of bird flocking are present in other instances of
collective animal behaviour. Fish schools, mammal herds and insect swarms represent
other examples of animal aggregations that have fascinated biologists for many years
(Gueron et al. 1996; Parrish & Edelstein-Keshet 1999; Krause & Ruxton 2002; Couzin
& Krause 2003). Like starlings, individuals form cohesive groups that are able to
sustain remarkable coordination.
Diverse instances of collective behaviour are found in many different fields of
science, from the spontaneous ordering of magnetic moments in physics (see, e.g.,
Cardy 1996), the coordination of an ensemble of artificial agents with distributed
intelligence in robotics(Cao et al. 1997; Jadbabaie et al. 2003), the emergence of
herding behaviour in financial markets in economics (Cont & Bouchaud 2000), to the
synchronized clapping in a concert hall (Neda et al. 2000; Michard & Bouchaud 2005)
or the Mexican wave in a stadium (Farkas et al. 2002). In all these examples, collective
behaviour emerges as the result of the local interactions between the individual units,
without the need for centralized coordination. The tendency of each agent to imitate its
neighbours (allelomimesis), can, by itself, produce a global collective state. Whenever
this happens, we are in the presence of self-organized collective behaviour.
Although self-organization is undoubtedly a general and robust mechanism, its
universality is an
…(Full text truncated)…
This content is AI-processed based on ArXiv data.