Figure 2.

A descriptive presentation of total aggression levels (chases, beak fences, pecks, threats) per minute off the nest as exhibited by unpaired and paired male zebra finches, treated either with VP antagonists (VPant) or with saline, toward male and female conspecifics, across six observation sessions. Aggression levels tended to be higher in paired individuals and to decline over time. Two sessions were conducted per day. The pattern shown here is virtually identical if the data are subdivided into male- and female-directed aggression, or are not corrected for time on the nest (see Results). Sample sizes are denoted in parentheses below session number. Data are shown as mean ± S.E.M. Because some males changed between unpaired and paired status, and were examined across sessions, the data must be subdivided for statistical analyses, as shown in Fig. 3.