Does song complexity correlate with problem-solving performance in flocks of zebra finches?

The 'cognitive capacity hypothesis' states that song complexity could potentially be used by prospective mates to assess an individual's overall cognitive ability. Several recent studies have provided support for the cognitive capacity hypothesis, demonstrating that individuals with more complex songs or larger song repertoires performed better on various learning tasks. These studies all measured individuals' learning performance in social isolation. However, for gregarious species such as the zebra finch, Taeniopygia guttata, testing individuals in a group context is socially and ecologically more relevant if song complexity is to be a meaningful indicator of cognitive ability. We tested whether song complexity correlated with performance on a suite of novel foraging problems in flocks of male zebra finches, starting by replicating the lid-flipping task used by Boogert et al. (Animal Behaviour, 2008, 76, 1735-1741), who provided the first support for the cognitive capacity hypothesis in zebra finches isolated during testing. We also presented flocks with a barrier task and two types of novel food. We found that males' song complexity scores did not correlate with their latency to solve any of these novel foraging problems in a social context. Individuals that solved the tasks likewise did not have more complex songs than nonsolvers. However, performance was positively correlated across the different foraging tasks. These results raise doubts as to whether the song complexity measures used by Boogert et al. are predictors of problem-solving performance, and perhaps cognitive ability, in a more ecologically relevant, social setting. Stress responsiveness might instead explain the association between song complexity and foraging task performance among isolated zebra finches reported by Boogert et al.