Two attributes of many temperate passerine species are short-term territoriality and strongly fluctuating annual testosterone (T) profiles. Circulating T of temperate passerines can vary from undetectable levels in the nonbreeding season to higher, but fluctuating, levels during the breeding season. Males of many temperate species respond to territorial instability during the breeding season with transitory increases in T. In females, the hormonal response to aggression is more complex. Most temperate-zone passerine species that have been studied exhibit territoriality for less than three months. Here, I describe the year-round T profile of male and female Northern Cardinals (Cardinalis cardinalis), a temperate-zone species with prolonged territorial behavior (7 months). Circulating levels of T in female Northern Cardinals is relatively stable. Males show variation in T levels over the year and they may respond to territorial intrusions with increases in T. Of particular interest are the relatively high levels of T observed in female Northern Cardinals throughout the year, and measurable amounts of T in both sexes in the winter.
Testosterona en Cardinalis cardinalis: Posible Influencia del Comportamiento Territorial Prolongado