The town where I live has a short but nice urban trail that manages to not be too urban. I've been tempted to hike it at night many times, but by far the most dangerous animal around is people. I'm always worried I'll come up on some meth head hiding his stash or something. I have been out on it a few times in the dark, but never too late or too long. Shame too, because there's lots of wildlife right here in town: owls, raccoons, lots of deer, etc. Just think about the dangers of your particular area and exercise due caution.