John,
You'll get a schit ton of advice on this. But if you want to hit them right now, I think dog speak is your best bet.
Here is a link to get an idea what you should sound like. He has a large sampling of sounds.
http://www.varmintal.com/ahunt.htmHere is an example of an estrus whimper. Should serve you well for the next few weeks. Skip to the 27 second mark.
http://www.youtube.com/watch?v=zskkZfShHWcI think the CrittR Call Song Dog is a good, easy howler to use but that is subjective of course.
I don't like electronic calls for two reasons. 1.) I'm lazy and I hate carrying extra schit. 2.) I'm lazy and I hate carrying extra schit.
Best of luck and ask away. Lots of good predator callers on here to help you out.
Travis