The use and misuse of public information by foraging red crossbills

Group foragers may assess patch quality more efficiently bypaying attention to the sampling behavior of group members foragingin the same patch (i.e., using "public information"). To determinewhether red crossbills (Loxia curvirostra) use public informationto aid their patch departure decisions, we conducted experimentsthat compared the sampling behavior of crossbills foraging ona two-patch system (one patch was always empty, one patch containingseeds) when alone, in pairs, and in flocks of three. When foragingalone, crossbills departed from empty patches in a way thatwas qualitatively consistent with energy maximization. We foundevidence for the use of public information when crossbills werepaired with two flock mates, but not when paired with one flockmate. When foraging with two flock mates, crossbills sampledapproximately half the number of cones on the empty patch beforedeparting as compared to when solitary. Furthermore, as expected ifpublic information is used, the variance in both the numberof cones and time spent on the empty patch decreased when crossbillsforaged with two flock mates as compared to when alone. Althoughhigh frequencies of scrounging reduce the availability of publicinformation, scrounging is usually uncommon in crossbills, apparentlybecause they exploit divisible patches. Consequently, publicinformation is likely to be important to crossbills in the wild.We also show that feeding performance is greatly diminishedwhen the feeding performances of flock mates differ. This providesa mechanism that will favor assortative grouping by phenotypewhen phenotypes affect feeding performance, which may in turnpromote speciation in some groups of animals.