After doing some content analyses, Morgan Worthy (I Have Known the Eyes Already) asked 100 ornithologists to make blind ratings of large families of birds on “quick-versus-deliberate” behavior related to flight, feeding, and escape:
Twenty-one agreed to do so. Some left out those families with which they were not very familiar.
I included in the analysis all large families of birds for which at least 15 ornithologists had made ratings. When size was partialed out, the eye-darkness measure and the combined behavioral measures correlated .56 [d.f. = 33, p < .001]. As you probably know, John, that means that differences in eye-darkness, even using a two-point scale, accounted for about 31% of the rated differences in quick-versus-deliberate behavior. That is not trivial. The family of birds that was rated most deliberate was herons; the family of birds that was rated quickest was swifts. Whereas the reaction time differences with humans were small in absolute terms, in this study of birds, the behavioral differences were large.