Data from: Size, ornamentation, and flight feather morphology promote within-pair paternity in a sexually dimorphic passerine

Morphology in sexually dimorphic species is related to increased opportunity for sexual selection when traits reflect individual quality. In socially monogamous species, it may function to increase variance in reproductive success if exaggerated traits are related to the opportunity to engage in extra-pair paternity (EPP). Nonetheless, it is poorly understood if ornamental versus functional traits are differentially related to the distribution of paternity across individuals. We examined EPP in the Scissor-tailed Flycatcher (Tyrannus forficatus), a sexually dimorphic suboscine passerine, to determine how flight feather morphology (both ornamental and related to flight performance), ornamental coloration, and flight performance were related to paternity for males and females. We assessed paternity at 140 nests across 7 years and found that 73% of nests contained extra-pair young with 59% of nestlings resulted from extra-pair fertilizations. Males that secured paternity with their social mate had larger size (wing chord and tail length), better body condition, and more exaggerated ornamental traits (color, primary notch, and streamer length) than cuckolded males. When compared directly to the social males they cuckolded, however, cuckolders had shorter primary notches and had duller coloration. Elongated flight feather features were associated with greater maneuverability during flight, and longer primary notches and tail streamers were associated with maintenance of within-pair paternity, possibly via flight displays. Females that cuckolded their mates had less exaggerated flank coloration but better body condition than those that did not. We posit that in this system there is a lack of strong selection on extra-pair mate morphology; rather, high quality males maintained WPP while females in good condition were more likely to cuckold social males of poorer quality, signaling a role of reciprocal selection in extra-pair mate choice.STFL male morphology - EPPmorphological data for extra-pair paternity dataSTFL male color - EPPcolor measurements for extra-pair paternitySTFL female morphology - EPPfemale morphology for extra-pair paternitySTFL female color - EPPfemale color for extra-pair paternitySTFL mensural - cuckoldpaired morphological data for cuckoldrySTFL color - cuckoldpaired color data for cuckoldrySTFL flight tubedata for maneuverability through flight tub