The effects of energy reserves and dominance on the use of social-foraging strategies in the house sparrow

In social animals, dominance rank often influences individuals' behaviour, but in most cases it is unknown how dominance modulates the effects of other phenotypic traits. We investigated the mutual effects of social dominance and the level of energy reserves on the use of social-foraging strategies in captive flocks of house sparrows, Passer domesticus. We used experimental wind exposure to manipulate overnight energy expenditure of dominant and subordinate individuals. In response to the experimental treatment dominants used scrounging (exploiting others' food finding) significantly more, whereas for subordinates there was only a moderate and nonsignificant increase in scrounging. Individual variability in the frequency of scrounging was higher in subordinates than in dominants and this difference between the dominance groups was unaffected by the treatment. These results suggest that individuals of different dominance status adopt different strategies: to cope with an energetically challenging situation, dominants behave rather uniformly by increasing further their preference for scrounging, whereas subordinates do not alter their tactic, but may rely on using scrounging opportunistically.