The use and misuse of public information by foraging red crossbills

Group foragers may assess patch quality more efficiently by paying attention to the sampling behavior of group members foraging in the same patch (i.e., using ‘‘public information’’). To determine whether red crossbills (Loxia curvirostra) use public information to aid their patch departure decisions, we conducted experiments that compared the sampling behavior of crossbills foraging on a two-patch system (one patch was always empty, one patch containing seeds) when alone, in pairs, and in flocks of three. When foraging alone, crossbills departed from empty patches in a way that was qualitatively consistent with energy maximization. We found evidence for the use of public information when crossbills were paired with two flock mates, but not when paired with one flock mate. When foraging with two flock mates, crossbills sampled approximately half the number of cones on the empty patch before departing as compared to when solitary. Furthermore, as expected if public information is used, the variance in both the number of cones and time spent on the empty patch decreased when crossbills foraged with two flock mates as compared to when alone. Although high frequencies of scrounging reduce the availability of public information, scrounging is usually uncommon in crossbills, apparently because they exploit divisible patches. Consequently, public information is likely to be important to crossbills in the wild. We also show that feeding performance is greatly diminished when the feeding performances of flock mates differ. This provides a mechanism that will favor assortative grouping by phenotype when phenotypes affect feeding performance, which may in turn promote speciation in some groups of animals.