>> Hoover and colleague Scott Robinson found that when they removed cowbird eggs from the warbler nests, those nests mysteriously got trashed. Turns out that the cowbirds, much like members of the mob, were keeping a close eye on the nests in which they had laid their eggs. If anything bad happened to the eggs, the cowbirds would return and destroy the nest.
Rational behavior for birds and gangs. Terrorists act rationally too. They're are to gangs what vodka is to beer.