title: Formation of linear dominance relationship in captive jungle crows (Corvus macrorhynchos): implications for individual recognition.
abstract: Jungle crows (Corvus macrorhynchos) flexibly change their social forms depending on their age, time of the day, and the season. In the daytime, paired adults behave territorially and unpaired subadults form small flocks of ten birds, whereas at night hundreds of birds roost together. In the breeding season, pairings remain in their nest all day. This fission-fusion raises questions about the underlying social structure and the cognitive capability of jungle crows. In this study, dyadic encounters were used to investigate dominance relationships (linear or non-linear) and the underlying mechanisms in captive jungle crows. Fourteen crows were tested in 455 encounters (i.e., 5 encounters per dyad), and a stable linear dominance relationship emerged. Sex and aggressiveness were determinants as individual characteristics for dominance formation. Males dominated females, and more aggressive individuals dominated less aggressive ones. Aggressive interactions in dyads occurred primarily during the first encounter and drastically declined during subsequent encounters without any signs of a confidence effect. These results suggest that, in captive jungle crow, a linear form of dominance is intrinsically determined by sex and aggressiveness and maintained extrinsically by memories of past outcomes associated with specific individuals, implying individual recognition.
authors.affiliation: Department of Psychology, Keio University, Tokyo 108-8345, Japan. izawa@psy.flet.keio.ac.jp
authors.forename: Ei-Ichi
authors.initials: E
authors.lastname: Izawa
authors.forename: Shigeru
authors.initials: S
authors.lastname: Watanabe
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001245:Association Learning; D046368:Crows; D004291:Dominance-Subordination; D005260:Female; D008297:Male; D021641:Recognition, Psychology; D012737:Sex Factors; D012931:Social Environment; D018709:Statistics, Nonparametric