Also see:
Rebirth of the Guinea Hens by Mark Bowden
The Atlantic, March 2011

Intelligent behavior in guineas, it seems, is an inverse function of their number, a truth long known about human beings. The large flock was good at only one thing: panic. Confronted with a threat, its members acted out a perfectly choreographed charade of a nervous breakdown, full of fluttering feathers and high-decibel clatter, and then succumbed to whatever had alarmed them.