RE: coyote mating season
There is a fairly new sound that has been documented that has been called a Female estrous chirp. The sound is made when a male is courting a female, wanting to breed but she isn't ready so to speak. The Predator or Prey/Verminator video has a clip of this in action. The estrous chirp is several mono toned yips with a pause, then several more yips several times over. There is also a howl known as the Female Invitation howl, and this is a higher pitched lone howl that is cut off, in other words, unlike a lone howl, the invitation howl cuts off instead of gradually descending in tone!
Both howlssounds seem to work especially well come mating season. Probably for two reasons: 1) most callers use distress calls all winter and not as much howling, 2) most callers start using more howling during mating season and this is when the coyotes will respond the best to vocals because of territorial instincts and breeding instincts.
Your basic howler that is capable of high picthed howls will work just fine in reproducing these sounds!