On the pack/solitary issue. I have seen both ways around here. About sundown they will group up, and for a while will yip, howl, bark, and just raise a ruckus in general. After dark, I often hear a single animal calling out. Sometimes, it will move a ways and call out again. Sometimes another animal will answer, sometimes not.
My guess is that while they are part of a pack, they split up to hunt. If they find something of interest to the whole pack, then they communicate it. I also beleave that they call out to keep track of where other coyotes are, and to let others know where it is at.
Without exception, the coyotes I have seen in daylight were all single animals. Randolph AFB is about 10 miles away, and the larger jets pass over on landing and take off. I seldom see the trainers out here. Anyway, there is a pack in a mesquite and brush pasture near me that will really raise cane when one of these jets passes over low. The noise must hurt their ears. This is the only time you will hear them in daylight hours.
Research done on coyote scat indicates they eat a wide variety of items, including vegatation, fruit, and insects. I think it's safe to say that coyotes will take the easiest meal to obtain. They will not use more energy to catch something, then they will recieve from the prey. If food bocomes scarce, then they are willing to go to greater extremes. But, IMO their energy intake and output is like an equation that must balence, and can never go into the negative.
Ernie