Abstract: Mating success may be dependent on multiple traits and behaviors. Phenotypic integration describes the pattern of covariance among these traits. If multiple traits interact to affect mating success, selection may increase this covariance, leading to the evolution of an integrated mating phenotype. A mating phenotype is an integrated suite of morphological, physiological, and behavioral traits. To explore the mating phenotype of the dark-eyed junco, Junco hyemalis , we investigated the relationship between testosterone (T) levels, aggressive behavior, age, and attractive traits, wing length, tail length and tail white. Peak T levels and tail white are correlated, indicating integration of morphology and physiology within the mating phenotype. To understand the broader context for this relationship, we performed simulated territorial intrusions (STIs) in which territorial males are presented with a male and song playback. We measured aggressive behavior as well as increase of T during the intrusion. We measured correlations among T, aggressive behavior and tail white in order to examine how behavior is integrated into the mating phenotype. We found that age by class, yearling and older, was significantly correlated with aggressive behaviors and individually songs, time in 5 m, and ptiloerections. In addition, we found that rise in T after GnRH challenges from 2003 and 2004 was correlated with aggressive behaviors, particularly song. We did not find any significant relationship between any morphological characters and aggressive behaviors. Our results suggest phenotypic integrations of physiology and behavior. In addition, the increase of aggression with age suggests a possible change in mating strategy as a male ages.