Figure 10.2 Increased vigilance when living in a group In the European goldfinch, an increase in flock size results in (a) an increase in the total number of head raises performed by the flock, (b) a decrease in the number of head raises performed by an individual, and (c) a decrease in the time required to husk a seed.

Data from E. Glück, Benefits and costs of social foraging and optimal flock size in goldfinches (Carduelis carduelis), Ethology 74 (1987): 65–79.