Every night at 3:15 or so, one of them starts to whine. If we move in the bed, she starts to bark. It used to happen at 6:30 AM or so, so we'd get up, let them out, feed them, and go back to bed. It's gotten earlier and earlier and earlier . . .
If we ignore them, they just continue to whine and bark -- keeping us awake in the process. So we always give in, which of course just encourages them to continue doing it night after night.