The aim of the present study was to examine the effect of area reduction on the hierarchy-dependent behaviors of wild boars and crossbred sows (wild boar X Vietnamese pot-bellied pig) living in captivity, with regard to a food competition situation. We first defined the hierarchy system among 7 individuals, living together for more than a year, with a mathematical model based on wins and defeats. We then tested the possibility of a correspondence between the rank position and the age and/or weight. In a first experiment, we defined the frequency of dominant and submissive behavioral elements depending on the rank and on the group level in a food competition situation. We analyzed individually the time spent feeding. In a second experiment, we reduced the size of their living area and observed the potential modifications of the dominant and submissive elements' frequency as well as the time spent feeding.We found a linear hierarchy among the sows. We did not find any relationship between the rank and the age or the rank and the weight of the animals. However, after excluding the youngest and the lightest leader from the analysis, significant correspondence was found among the aforementioned variables. In such cases, the older and heavier sows occupied the higher ranks in the hierarchy. We also observed that the sow with the higher rank position spent more time feeding and presenting aggressive behaviors compared with the other individuals, whereas the sow with the lowest rank position spent the most time displaying submissive behavior. Moreover, the frequency of dominant and submissive behavioral elements increased when reducing the size of the living area.Based on our results, we found that the area reduction and, therefore, the higher density increased the frequency of aggressive and submissive behavioral elements of the sows. (c) 2012 Elsevier Inc. All rights reserved.
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