246 POTENTIAL BETWEEN BRAINSHowever, empirical data show that the total response is faster than
such ripples: changes of speed among diff er ent birds are correlated be-
yond the infl uential neighbors. Th e changes seem to be cast near instanta-
neously through the fl ock as a whole. Th is obviously enhances a predator
escape maneuver, but its mechanism is not clear.
Irene Giardina and colleagues studied fl ocks (or murmurations) of
common starlings. Using multiple video cameras, they tracked and ana-
lyzed fl ock movements from second to second. Th ey showed that changes
in the velocity of any one bird aff ected the velocity of all other birds in a
fl ock, regardless of the distance between them. Th at sort of relationship
is known as a scale- free correlation, and is seen in systems poised at the
edge of criticality. Such dynamics are typical of attractor landscapes, like
the metabolic interactions in cells and pro cessing in nerve networks, as
described in previous chapters.^10
As with players on a soccer team, properly aware of one another, “the
change in the behavioral state of one animal aff ects and is aff ected by that
of all other animals in the group, no matter how large the group is. Scale-
free correlations provide each animal with an eff ective perception range
much larger than the direct inter- individual interaction range, thus en-
hancing global response to perturbations. Our results suggest that fl ocks
behave as critical systems, poised to respond maximally to environmen-
tal perturbations.”^11
Remember from chapter 4, and the Bénard cells, that a critical point
is where distant ele ments of a system become correlated with one another,
far beyond the range of local interactions among the individual ele ments.
As William Bialek and colleagues say with regard to bird fl ocks, “Th e
critical point is the place where social forces overwhelm individual pref-
erences;” it is where “individuals achieve maximal coherence with their
neighbours while still keeping some control over their speeds.... Away
from criticality, a signal vis i ble to one bird on the border of the fl ock can
infl uence just a handful of near neighbors; at criticality, the same signal
can spread to infl uence the be hav ior of the entire fl ock.”^12 In other words,
the dynamics of the fl ock is a far better way to make predictions from
fl eeting signals than the use of built-in rules or personal learning.
Th e study of fl ocks is thus instructive for understanding group dy-
namics. Birds are more adaptable than ants as individuals. But they bring
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