This is the time of year I use howls to bring them in. So far, I have never had one howl back at me, so when they come in, they come in fast and quiet.
I think every coyote knows the voice of every other coyote within his hearing ability, so when I show up and howl, it's "who is this guy?" and they investigate. It's kind of like my house, if I hear a strange voice inside, I am coming to investigate.
When coyotes howl in the AM and PM, I think they are doing a 'sound check' of who survived the night/day. If a coyote doesn't howl for a few days, their territory is now up for grabs, which is why I'll hunt the same place every week if I kill the coyotes that respond to the calls. Existing coyote gets killed, new ones move into the vacancy.