I study a single "slow" bird moving with a flock of birds of a different, and
faster (or slower) species. I find that every "species" of flocker has a
characteristic speed Ξ³ξ =v0β, where v0β is the mean speed of the
flock, such that, if the speed vsβ of the "slow" bird equals Ξ³, it
will randomly wander transverse to the mean direction of flock motion far
faster than the other birds will: its mean-squared transverse displacement will
grow in d=2 with time t like t5/3, in contrast to t4/3 for the
other birds. In d=3, the slow bird's mean squared transverse displacement
grows like t5/4, in contrast to t for the other birds. If vsβξ =Ξ³, the mean-squared displacement of the "slow" bird crosses over from
t5/2 to t4/3 scaling in d=2, and from t5/4 to t scaling in
d=3, at a time tcβ that scales according to tcβββ£vsββΞ³β£β2.Comment: 10 pages; 5 pages of which did not appear in earlier versions, but
were added in response to referee's suggestion