Perhaps there's something they need from those animals....some sort of nutrients, maybe genetic material or something. I also think with people, they are keeping eyes on them how they are, like when we catch and tag and animal and release them. And as I mentioned, we're dealing with aliens, whom might have a completely different mentality than we do. Also, I have heard of various hybrids being made and they are let into our own world and blend in, it's a pretty interesting way to learn things....also, I have seen really weird looking folks and gotten.....interesting vibes, like they are really not from around here. Maybe they are also tying to improve themselves and/or ourselves. Also, like I said, some are probably good, some are probably bad. We gotta learn about them and be aware of their existence first before getting all the other answers.