Using priority to food access: fattening strategies in dominance-structured willow tit (Parus montanus) flocks

Abstract

We studied changes in body mass in response to priority to food access by repeatedly weighing free-living willow tits in dominance-structured flocks. Priority to food access did not correlate to either acquisition rate or net turnover of body reserves, but subordinates with low food availability had larger body reserves than dominants. Removal experiments suggest a causal relationship between rank and the size of reserves. Body reserves of subordinates decreased when their access to food increased after the dominant was removed. Low variability in body mass of subordinates shows that they do not maintain large reserves in response to uncertain acquisition of food. Rather, large reserves of low-rank individuals could serve as insurance for conditions with increasing requirements. Under such conditions, dominants are more likely to claim their priority to food, and subordinates would not be able to increase their body reserves by feeding.