Couple 1 (photo 1) was inspecting the hollow with couple 2 (photo 2) watching from adjacent tree. The two males squared off (photo 3) before male 1 attacked male 2 (photo 4). Both couples hung around the hollow for about 5 minutes while I was there before couple 1 headed south and couple 2 headed north. Female 2 stayed relatively close to the hollow for 15 minutes after this.