Late in the season last year (late October/early November) the male Shadow Darners and Happy-face Darners outnumbered the females at Cranberry Lake by quite a ratio. In fact, we seldom saw females, and in locations where we would normally see 2 - 4 male darners perched we now saw 15 or more. In addition, the males seemed to be particularly aggressive toward one another – certainly more so than we had seen earlier in the season. Rather than simply fly toward a rival until it turned and left the territory, the males would come into physical contact, and grab at one another with their legs.
The following video from the Dragonfly Whisperer channel on YouTube shows two male darners grabbing one another and spinning round and round like two Bald Eagles with locked talons. They almost fall into the water, but separate just in time. They then gain some altitude and go at it again. This is quite different from the interactions earlier in the season, which generally don't result in any direct contact. Here's the link to the video:
https://www.youtube.com/watch?v=9UVUxjbhYA0
