The establishment of foraging flocks in house sparrows: risk of predation and daily temperature

Summary The foraging decisions of animals often reflect a trade-off between the risk of predation and efficient foraging. One way an animal may reduce the risk of predation, and hence exploit a resource patch in relative safety, is by foraging in a group. Solitary pioneer sparrows often recruit others to a food source by making chirrup calls in order to establish foraging flocks. This study describes the decisions of house sparrows that arrive at food resources of different risks of predation. Four feeding sites at different distances from a perching site and from an observer were presented to sparrows. When the feeder was adjacent to the perching site and far from the observer, the pioneers chirruped less frequently and were more likely to forage alone than when the feeder was in the other three positions. There were differences in the scanning behaviour of sparrows at these sites, suggesting that they were responding to different risks of predation. Furthermore, the chirrup rates of pioneer sparrows in this study and a previous study were found to be negatively correlated with maximum daily temperature. This is consistent with the hypothesis that energy requirements may affect the flock establishment decisions of sparrows, and that the benefits of foraging in flocks may be greater at lower temperatures.