Birds are well known for their sexual dimorphism. But not all forms of dimorphism are the same, and differences in morphology can be so subtle that they aren’t detected by casual observation. We report that this is the case with the Sulawesi Babbler (Pellorneum celebense), the first reported instance of sexual dimorphism in this species or any of the ground babblers of the Southeast Asian islands. Our finding is based on a combination of morphometric...