In the space of two days, I witnessed two examples of bird-on-bird aggression. One was of a form I'd seen before, but the other was new to me. None of the photos is especially good, but they seem worth sharing anyway.
The more familiar incident took place earlier today (May 14, 2023). As I watched, a pair of Western kingbirds chased a raven out of their nesting territory. This happened up-sun from me, and my images suffered accordingly. In the most decent image, one of the kingbirds is attacking the raven in mid-air. Sometimes size isn't what wins fights, it's being brave and pissed off at the same time.
Now for the incident that took place the day before, and that still puzzles me. In this case the images suffered from being taken in the shade. As I watched, two male-female pairs of summer tanagers (Piranga rubra) joined up in a bush. The two females dropped to the ground and began fighting (or maybe the fight started in the bush). A male flew down and took a ringside seat, but didn't interfere. A few seconds later the second male flew down and also took a ringside seat, and also didn't interfere. A few seconds after that, all four birds flew away. Afterwards, one pair was quickly gone but the other pair stuck around for a bit. Perhaps this was a fight over nesting territory, but I've never heard of female birds fighting while the males watch. If you know what's going on in these pictures, I'd be glad to hear from you.