I'm bored on a frigid sunday morning, so here's a link to my response on another thread about what calls to use and when:

Coyote Hunting Call Questions

That will get you to the thread, which has several responses, but I'll copy my response below. This "dissertation" describes my experiences with when to use different call sounds for coyotes:
-----------------------------------------------------------------------------------------------------------------------
Over the last 20yrs+ of calling coyotes, I'd be confident that 90% of my dogs have been drawn in by cottontail distress sounds.

For me, it's pretty simple. Certain sounds work great certain times of year, while other times of year, they'll be hit or miss. The sound of a free meal is great all year long, so why not use that as your go-to call? I use higher pitched cottontail or rodent distress because it's an easier meal than larger animals, like jackrabbits, or fawns/deer. Bird distress sounds are good most of the year too, and are really good for drawing in bobcats.

I occasionally bring dogs in on coyote vocals, but they're more selective for certain times of year.

Specifically:

Female in heat sounds/whimpers: B1tches come in heat generally late winter, so I'll usually only use female wimpers in late january, or February through march.

Female invitation: Female howls are good through most of the year, but do very well for me in the breeding season, late jan/early feb through march.

Male territorial howls and challenge barks: Coyotes are very territorial during mating season, welping, clear up through when the pups are mobile. Male coyotes will get very bold in Jan-March, so they'll investigate intruding males like crazy.

Pup distress: Pups are generally born in April to May, so I'll use super high, low volume, short "peeps" of pup distress during that time. Then through the summer, the pups will be getting bigger, more mobile, and their voices will change. By late July-August, I'll use some small pup barks, then pup distress with more power, volume, and length.

Fawn distress: I'd keep it around mid-late spring to early summer (april-june timeframe), since that's when the whitetails are usually dropping fawns.

Turkey vocals: It seems that turkey sounds work best during mating through the first month or so of a new hatch, between March up through June.

All that seems like an awful lot to keep track of, and for what it's worth, not many of those timelines match up well with prime fur conditions. The simple solution is distress calls. Coyotes have to eat all year round. Sound like an easy meal, and they'll come.

One bit of good news is that in the fall, you'll see a LOT of adolescent coyotes running around that don't have a CLUE what's going on yet. No, they're not very big yet, but younger dogs are super easy to call. A desperate, exciting distress call with a lot of action and emotion will bring these pups in at a run.

I'll also second the recommendation to visit predatormasters.com. Absolute wealth of information and a great bunch of guys to learn from. Spend some time reading over there and you'll start to see that there's a big difference in the knowledge base between a "guy that hunts coyotes", and a "coyote hunter".
------------------------------------------------------------------------------------------------------------------

That pretty much sums up my experiences for how and when different call sounds SHOULD work, but the more you call coyotes, the more you'll see that there are no hard and fast rules.