LYNN , Sharon E.*; WINGFIELD, John C.; The College of Wooster; University of Washington: Dissociation of testosterone and male-male aggression in breeding Chestnut-collared longspurs, Calcarius ornatus

Among males of many avian species, elevated testosterone (T) and aggressive behavior appear to be related: expression of aggression is accompanied by a rise in T secretion, and elevated T in turn affects persistence of aggression and promote readiness for future agonistic encounters. However, in some species, this relationship appears subtle or nonexistent. We have previously shown that male Chestnut-collared longspurs (Calcarius ornatus) exhibit a rise in plasma T early in the breeding season; later, as nests are initiated, plasma T declines to a breeding baseline. In addition, in this species, experimentally prolonging the early season T peak increased male sexual behavior before eggs hatched, but did not affect nestling provisioning. In the current study, we used simulated territorial intrusions (STIs) to investigate interactions of high T and male-male aggression in this species. We tested (1) if males increased T secretion following STI early in the breeding season (2) if behavioral response to STI changed as T levels declined from the seasonal peak to the breeding baseline, and (3) if experimentally elevated T enhanced aggression when T levels were at the breeding baseline. We found that plasma T was unrelated to duration of STI before nests were initiated. In addition, although males responded more aggressively to STI prior to nest initiation than during the incubation period, experimental elevation of plasma T to pre-nesting levels did not enhance aggression during incubation. Although the seasonal plasma T peak and expression of aggressive behavior overlap temporally, our data suggest that high plasma T and male-male aggression may not be fully coupled in this species.