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Producer-scrounger roles and joining based on dominance in a free-living group of Mexican jays (Aphelocoma ultramarina)
McCormack, John E., Piotr G. Jablonski, and Jerram L. Brown
While foraging, animals often exploit group members to obtain food. One way to describe this behaviour is with the producer-scrounger (PS) model, where scroungers use social interaction to obtain food discovered by producers. Mexican jays (Aphelocoma ultramarina) are a group foraging species with a linear dominance hierarchy. We studied interactions in a free-living foraging group to determine (1) if foraging interactions can be explained with the PS model, (2) if these roles are consistent and (3) if dominance or relatedness affects joining frequency. We recorded board-flipping, eating, and joining events during sets of feeding trials. We show that Mexican jays use PS roles and that these roles were consistent through many trials, but might have changed between trial sets. Relatedness and frequency of joining were not correlated. Dominance influenced joining in that joining was more likely to occur between birds with a larger difference in their dominance rank. In contrast to other studies, our results suggest that this effect is mediated through joiner preference. Scroungers preferentially joined birds of lower dominance rank and high search activity. Producers with these qualities had fewer eating events with full access to seeds, suggesting that scrounging exacts a cost on producers.