Courtship display behavior influences tail myology in Centrocercus minimus (Gunnison sage-grouse)

A variety of bird species engage in complicated, elaborate courtship displays to impress potential mates. Such displays include wing flaring, aerial acrobatics, choreographed dances, and tail fanning. Though these behaviors are often well studied, the underlying musculature facilitating them is poorly understood. Exemplars of unique avian courtship behaviors include species of the North American sage-grouse (Centrocercus). Each spring, males gather in leks where they perform courtship displays which incorporate species-specific sound production, nape feather movement, and importantly, the raising and spreading of their rectricial fan for prolonged periods of time. Here we describe the tail myology of the lekking sage-grouse species Ce. minimus (Gunnison sage-grouse). We compare the tail myology of this species to that of other, either closely related or similarly sized, bird species which do not engage in rectricial displays. Results indicate tail myology in Ce. minimus is adapted for unique courtship behaviors. Muscles of the rectricial apparatus in Ce. minimus have greater proportional mass relative to body mass compared to other species examined here, and nearly all other species previously examined. In particular, both overall mass and the mediolateral width of the origination surface of the m. levator caudae are hypertrophied compared to other species which do not incorporate a raised tail fan during courtship displays. Additionally, the muscles that primarily spread the tail fan have relatively more extensive origin surfaces in Ce. minimus. Our results provide evidence that the specialized courtship behaviors of Ce. minimus have a clear influence on the tail myology morphology of this species, and suggest that sexually selected displays alter the corresponding underlying musculature across birds.