An Analysis of Dominance, Its Behavioural Parameters and Possible Determinants in a Herd of Icelandic Horses in Captivity

Abstract

The applicability of the concept of dominance was investigated in a captive herd of 26 Icelandic horses and 5 ponies of different breeds. Eight out of 20 behaviours possibly related to dominance occurred frequently enough to be investigated in detail. For these eight agonistic behaviours the coverage, the unidirectionality in the exchange, and the degree of transitivity (Landau's linerarity index) were calculated. Four offensive behaviours, together with avoidance, were suitable for further analysis with regard to dominance. The patterns of asymmetries with which these behaviours were exchanged were sufficiently similar as to justify the application of the dominance concept and to construct a (nearly) linear dominance hierarchy. The rank order of the castrated stallions was completely linear. the hierarchy of the mares was almost completely linear. The results suggest that offensive and defensive aggressive behaviours should be treated separately and that the concept of dominance is applicable. However, ritualized formal dominance signals between adult horses appear to be (almost) absent. The rank positions of the individuals were correlated with age and residency in the herd but not with height. Middle ranking horses tended to be more frequently in the close vicinity of an other horse than high ranking or low ranking horses. Over and above this correlation at the individual level, ii was found that pairs of horses close in rank to each other were more often also spatially close to each other. Being in oestrus did not influence the dominance relationships between mares. For castrated stallions the rank positions were correlated with the age at which they were castrated. This suggests that in male horses experience prior to neutering influences the behaviour afterwards.