Choice in free-ranging wild pigeons. 
A flock of free-ranging wild pigeons were trained to peck at buttons which, when operated, allowed brief access to grain.  Although only one bird at a time could have access to the buttons, the pecks of the group were treated as an aggregate.  When they chose between two buttons, each of which could occasionally produce grain, the ratios of pecks at the buttons approximately equaled the ratios of the grain presentations obtained from them.  This accords with a relation well substantiated in the laboratory, the matching law.  It suggests that the matching law may apply to the behavior of higher organisms in natural environments.