On May 6, 1960, when male 2 (1960) was in the process of usurping an eastern segment of the original territory of male 1 (1960), a violent, protracted dispute was observed. By this date male 1 (1960) had obtained a mate and had begun construction of nest 1-a (1960); male 2 (1960) had not yet acquired a mate. At first the two males were singing vigorously, from one to 10 feet apart. Female 1 (1960) followed her mate closely and scolded, at the same time partially fanning her tail. In the course of vocal dueling the males had traveled to within 50 feet of nest 1-a (1960), when male 1 (1960) suddenly lunged at 2 (1960). The males plunged to the ground, locking bills and clutching at each other with their feet as they fell. As soon as they touched the ground they separated. Male 2 flew east with male 1 in pursuit. This conflict lasted three minutes. Additional physical combat was witnessed several minutes later. This again involved striking with the bill, wings and feet. A high pitched squeaky _chee_ was uttered by both combatants. The female scolded from a nearby perch. Upon separating, the males engaged in a wild, looping flight. At about 350 feet from nest 1-a (1960), the chase abruptly ended. For ten minutes thereafter, both males sang at a high rate from perches about 10 feet apart. This terminated the physical combat, but three additional protracted, vocal duels occurred in the remainder of the morning. TABLE 3. INTRASPECIFIC DISPUTES IN MAINTENANCE OF TERRITORY. Behavior ============================================================== | Number | | | Average | of | Vocal | | length of | conflicts | dueling | Combat | disputes -------------+-----------+---------+--------+----------------- Prenesting | 3 | 3 | 2 | 6 min. 40 sec. Building | 8 | 8 | 6 | 3 min. 8 sec. Incubation | 1[B] | 1 | ... | 20 min. +-----------+---------+--------+----------------- Totals | 12 | 12 | 8 | 5 min. 30 sec. -------------+-----------+---------+--------+----------------- [B] Directed against a stuffed Bell Vireo. Probably as a direct result of these conflicts, a neutral zone approximately 300 feet wide developed between the two territories. By May 14 this intervening area was occupied by male 4 (1960). By this date both 1 (1960) and 2 (1960) were involved in nestbuilding and 4 (1960) was not challenged for several days.