A couple of reasons that mating season might effect calling. For one, by that time most coyotes have heard the waa waaaa rabbit blues enough that they almost run when the hear the sound. SO switching to coyote vocals for calling becomes a more effective tactic. And the obvious, by the time Feb. rolls around, the coyote numbers have dropped. Fewer coyotes to call. The man that can bring in numbers all winter long knows how to change hunting strategys with the conditions and time of year.

Sure, in the summer there is more food plus the coyote needs to eat more and eat more often in the winter to survive. Less food and cold temps. equals better calling conditions.And as yodeldog mentioned, with the taller and fuller vegetation, it's just tougher to see a coyote in the summer. Coyotewill eat fruit, vegetables, corn, mice, rabbits,carion, insects, etc.

IMO, unless you're going to find the den with pups, it's best to leave the late spring/pup rearing season, hunting for later in the fall.