78 evolution: the ages and tomorrow 



of predators is restrained by spacing, and a pair of birds is 

 reasonably assured of a food supply at the critical time of 

 rearing their young. 



Flocks of birds stratify into a complex order of domi- 

 nance and subordination and by this method greatly reduce 

 what might otherwise be a chaotic intraspecies struggle. 

 Allee has shown that a society of hens is organized into a 

 "peck order" in which a hen has the privilege of pecking 

 all other hens below it in the order without precipitating a 

 fight. When a flock of hens is first established, conflict be- 

 tween the birds breaks out and there is a degree of chaos for 

 a time. Individual birds fight and the winners of these 

 fights assume dominance over the losers; they may peck or, 

 as is most often the case, merely threaten to peck the loser 

 without remonstrance. Losers may win in fights with other 

 individuals and soon a stratification in peck order is set up— 

 a stratification that leads to a degree of peaceful living. Allee 

 found that dominance depended on many factors: size, 

 aggressiveness, the luck of battle, and so forth. One encoun- 

 ter was usually enough to settle the question, and each bird 

 would remember who had won and who had lost. Aggres- 

 siveness was most important and possibly due to hormones. 

 Some birds took a lower position in the peck order without 

 ever putting up a fight, and younger birds usually lost to 

 older. In the peck order we have a "social hierarchy," a con- 

 dition we find in the societies of many other animals, includ- 

 ing man, where there are the aggressive and the meek, a sit- 

 uation sometimes leading to abuse. 



Since leadership is almost certain to exist in a social hier- 

 archy, investigators have long been curious as to how leaders 

 became leaders. More often than not among birds, the leader 

 does not seem to be an individual of top rank in the peck 

 order. When a flock of hens has been released from a pen, 

 where dominance was established, observers have often 

 noted that a bird of mid-social rank takes on the leadership, 

 even though the peck order seems to remain the same. 



