RESUMEN
A refined analysis of the peck order in chickens was offered as a test of the notion that for this species, different responses such as leaping and various types of pecking need not be interchangeable indexes of aggression. Indeed, tests showed that particular response types of the birds were differentially mediated by organismic or environmental factors. In large cages pecking at the body was most frequent by birds that had a home-cage advantage. Contrarily, rates of aggressive leaping were independent of this environmental influence, with males having an advantage over females. Males showed more head pecking than females, but the profile for this sex difference did not resemble the profile for leaping. Correlational analyses revealed that whereas head pecking between testmates was not matched in frequency, leaping was positively related. Finally, the behavior of birds tested in small cages differed from that of the large-cage subjects. Although there was more head pecking in the small cages, males did not have an edge, and leaping was infrequent. Such results indicate that these responses cannot be viewed as interchangeable indicators of aggression in fowl.