They spawn when you throw the bait.
You can test this by sitting in one place (on a roof or high on some rocks to be safe), throwing some bait, killing the predator, and then collecting bait from its body.
You can repeat this indefinitely, especially if you're good with a bow since you can recover the arrows. Even if you throw bait dozens of times in a row, the predator will approach within a couple of seconds. This makes it clear that they're spawning since there are never that many predators naturally roaming so close a given location.