Behavioral Plasticity Favors the Retention of Both Assessment Strategies

quality mate, finding collaborators that may help to raise young, and to avoid inbreeding). It is the final point, where both can be useful in the same context, that our opinion diverges most strongly from that of Sheehan and Bergman, who suggest that the targets of social recognition and quality signaling are likely to differ. We have intensively studied a species for the last decade that employs both assessment strategies. Although this may bias our view, we believe this makes a good case study of why the 2 assessment strategies do not necessarily trade-off against one another. In the pied babbler (Turdoides bicolor), we have considerable evidence for social recognition (Humphries 2014). This fits with the hypothesis that Sheehan and Bergman acknowledge that species living in small stable social groups should develop social recognition (Tibbetts and Dale 2007). We also have considerable evidence for quality signaling. There is large individual variation in the male advertisement call in pied babblers, with the duration of the call correlated with male body mass and the likelihood of females responding (Humphries 2014; Ridley AR, unpublished data). Males typically bias the production of these calls toward extra-group females that are available to mate, further suggesting the use of the call as a quality signal (Humphries et al. 2015). Pied babblers therefore employ both assessment strategies on a regular basis, with the information in some cases being additive (using calling as a quality signal, but only directing it toward nonrelatives and extra-group females) rather than redundant. This is similar to that of the Harris’ sparrow (Zonotrichia querula) originally mentioned by Rohwer (1982) in his theoretical development of badge stability, where although Harris’ sparrows in large groups may find the use of a quality signal more reliable than in small groups, social recognition was still useful.