Meeting Abstract

26.1  Saturday, Jan. 4 13:30  Examining the relationship among foraging style, rectricial morphology, and the caudal skeleton in birds FELICE, RN*; O’CONNOR, PM; Ohio University ryanfelice@gmail.com

The tail represents an important locomotor module in modern birds, complementing the role of the wings during flight. The shape of the tail fan determines its aerodynamic properties and thus varies among birds that utilize different flight behaviors. This study tests two hypotheses: that tail skeletal morphology, like tail feather shape, is correlated with flight behavior and that tail skeletal and feather morphology are in turn linked. Skeletal and integumentary anatomy was quantified using linear metrics and geometric morphometrics in 51 species of birds. The relationship between caudal skeletal morphology and flight behavior was tested in a phylogenetic comparative context using phylogenetic MANOVA, regression, and flexible discriminant analysis. Pygostyle shape accurately predicts foraging behavior but not flight mode. Plunge- and pursuit-diving birds exhibit an elongate pygostyle, with aerial and terrestrial foragers possessing a short, dorsally deflected pygostyle. Convergent evolution of a common pygostyle shape in diving lineages (Alcidae, Phaethontidae, Phalacrocoracidae, Spheniscidae, Sulidae) strongly suggests that this morphology is related to the functional demands of using the tail as a rudder underwater (e.g., dissipating the increased mechanical loads experienced in the aquatic environment). Moreover, pygostyle shape is significantly correlated with and accurately predicts tail-fan shape. A forked tail fan is correlated with a dorsally deflected, hourglass-shaped pygostyle, whereas a graduated tail fan is linked with an elongate, tapered pygostyle. Taken together, these results indicate that avian caudal skeletal morphology is influenced not only by its function as part of the locomotor apparatus, but also as part of an integrated tail apparatus and fanning mechanism.