The last one I encountered, just the other week, was panicked by a speeding car coming the other way. I was doing my usual 60k/h but the other car spooked the roo, a big male, and it crossed between us. Luckily, neither of us hit it but it was close. I estimated that I would have hit it had I been going faster, say 80 instead of 60, in the 100k/h stretch. This was on the narrow hilly winding road I have to go on to get to town, before I join the main Highway.
The lesson for me is to slow down even more if the odd car coming in from opposite direction looks like it's speeding.