Lone Pine recently introduced a new species of macropod, a group of wallaroos. In spite of being there for over a month, they are still shy of humans and will bound away if any get too close, hoping to feed them.
I observed a big male chase away another, smaller, male and I thought I should come in for a closer look. It looked very much like territorial behaviour, which would be very unusual because kangaroos, being a nomadic and herd-based species, are not prone to territoriality. The male had adopted a large tree (right), underneath which are many low lying branches, making it a refuge from humans. The smaller male kept coming in and he would be challenged by the larger. Not yet ready for a show down, he would always back off but still stay in the general area.
Meanwhile, I sat on the ground and waited. I hoped to show them that humans were not a threat, by remaining perfectly still and only observing. Eventually, the male started challenging me. He would emerge from the cover of his tree and, clucking1 loudly, he would approach me by walking sideways, keeping his eyes on me the whole time. When he got as close as he would dare, he would stand off against me, displaying his impressive erection2. When this proved ineffective, he would make a loud clapping noise on the ground with his hind feet. It looked very much like a territorial display, and was meant to cow me into backing away. Maybe he thought I was after his females. He would always dart back under his tree and periodically he would perform a perfunctory mount of a female he had with him. It looked more like an assertion of possession than a serious attempt at mating.
I was never concerned for my safety, but I was certainly conscious of it. I kept my eyes on him the whole time, partly to show him I wasn't initimidated and partly to make sure I'd know about it if he made any sudden movements, and I was ready to get up quickly if I felt the occasion demanded it. He sometimes got close enough that he could have caused me an injury with his powerful hind feet and raking claws.
He repeated this display several times, but I was never able to get a decent photo off because he was still very wary of me and I didn't want to startle him. Unfortunately, the experiment had to be aborted after too many of my fellow humans came too close and upset the dynamic. I had been sitting there for the better part of an hour and one leg was suffering from lack of blood.
Even after he lost his tree, he was still agressive and kept chasing other males and even females of his own species. But only his own species. I was the only one of a different species that he saw fit to threaten.
1 Males also cluck gently to the females when they hope to mount one, but this wasn't the same sort of clucking. This was louder, faster, and definitely had a threatening edge to it.
2 Is this an example of convergent evolution? Many primates exhibit their erect penis in one way or another as a form of threat posturing. Humans also used to do this until quite recently, and still do it today in more subliminated ways.