Arginine vasotocin (VT), and its mammalian homologue arginine vasopressin (VP), 
are neuropeptides involved in the regulation of social behaviors and stress 
responsiveness. Previous research has demonstrated opposing effects of VT/VP on 
aggression in different species. However, these divergent effects were obtained 
in different social contexts, leading to the hypothesis that different 
populations of VT/VP neurons regulate behaviors in a context-dependent manner. 
We here use VP antagonists to block endogenous VT function in male zebra finches 
(Taeniopygia guttata) within a semi-natural, mixed-sex colony setting. We 
examine the role of VT in the regulation of aggression and courtship, and in 
pair bond formation and maintenance, over the course of three days. Although our 
results confirm previous findings, in that antagonist treatment reduces 
aggressive mate competition during an initial behavioral session during which 
males encounter novel females, we find that the treatment effects are completely 
reversed within hours of colony establishment, and the antagonist treatment 
instead facilitates aggression in later sessions. This reversal occurs as 
aggression shifts from mate competition to nest defense, but is not causally 
associated with pairing status per se. Instead, we hypothesize that these 
divergent effects reflect context-specific activation of hypothalamic and 
amygdalar VT neurons that exert opposing influences on aggression. Across 
contexts, effects were highly specific to aggression and the antagonist 
treatment clearly failed to alter latency to pair bond formation, pair bond 
stability, and courtship. However, VT may still potentially influence these 
behaviors via promiscuous oxytocin-like receptors, which are widely distributed 
in the zebra finch brain.