I think it's a combination of all three to be honest with you. I have been out only a couple of times this winter, and have hit some of my favorite spots with not a lot showing up.
If you don't get much this winter, don't worry about it. Here stortly is my favorite time to hunt them anyways. Spring!
The winter stuff is great, and produces pretty well, BUT if you really want to get more yotes, wait until they start dropping their pups and start using a puppy in distress call! Hardly anyone uses it, and even less people hunt for yotes in the warming months, but if you do, it pays off. Its a lot easier for both you and the coyotes to move around, and they seem like they are in a hell of a hurry to get to the pup sound. I am not sure if its for food, or if they think its their pups, but they tend to come in quicker than in the snow. Sometimes you even get a couple from different directions even.
NRA Certified Instructor: Pistol, Personal Protection in the Home. (MN Carry Permit)