The effect of dominance rank on fat deposition and food hoarding in the Willow Tit Parus montanus -: an experimental test

We studied the effects of dominance rank on fat deposition and hoarding behaviour in Willow Tits Parus montanus . Dominant individuals can displace subordinates which gives them priority to new food sources; they can also pilfer stored food from subordinates. This gives subordinates less certain access than dominants both to their own caches and to new food sources. Theory predicts that subordinates should invest more than dominants both in body fat reserves and stored food. Empirical evidence is equivocal; some studies have shown that subordinates built up larger reserves than dominants, whereas others show the opposite. In an earlier indoor experiment, Pravosudov and Lucas found no effect of rank on either hoarding rate or fat reserves, but the experimental design was such that the results were ambiguous. This paper reports on a similar, but improved, experiment in outdoor aviaries. However, our results agree with the earlier experiment, since we found no effect of rank on either food storing or fat deposition. The reasons for this are explored.