International Journal of Comparative Psychology

Comparative studies have yielded substantial insight into the functional relationships between the brain and behavior in birds. There are, however, important limitations to this method and problems can arise in the interpretation of the results. I use as an example, a test of whether interspecific brood parasitism is correlated with relatively smaller brains in the cuckoos and allies (Cuculiformes). Both conventional and phylogenetically based comparative statistics were used in conjunction with three alternative phylogenetic trees of the species examined. The comparisons between brood parasitism and relative brain size yielded mixed results, depending upon both the statistical method and the phylogeny employed. Although this could indicate that the evolution of interspecific brood parasitism is not related to relative brain size, the limitations of the comparative method in conjunction with the mixed results make it impossible to determine this with any certainty. The fact that different phylogenetic relationships yielded different results highlights the importance of phylogenetic relationships in assessing brain-behavior relationships. The continued use of phylogenetically based comparative methods should therefore be done cautiously, particularly with respect to interpretation of the results as the outcome may be as dependent upon the phylogeny as it is on the data itself.