Thanks, Cody...yeah, this is the first I've seen on them since I've had the girls, and I handle them fairly frequently. I think if they were there for some time, I would have seen something.
The snakes don't seem bothered by them, and I can find none of the telltale traces of them in the tank that I've read about (no dead mites in the water, etc). They may very well be birdie mites, but you can imagine my panic upon finding them! I immediately did a complete breakdown and substrate change on the spot, and haven't seen a mite since or before. My roomate has been taking the bird outside fairly frequently over the past few days; maybe he picked up something then. I'll tell her tomorrow morning so she can look him over. In the meantime, I'll be picking up some Prevent-o-mite tomorrow I think.