I don't think it has to do much to do with them wising up although Idon't doubt what you say.I think they're just extremely susceptible to dieases such as mange and I believe distemper.I'm out and about quite a bit and I've seen less sign the last few years,even in the areas that have more deer.They certainly take deer from time to time but their impact isn't as high as some would like you to believe.In good habitat,where the fawns have cover and the nutrition to put on weight fast,there isn't a big impact.We can debate that all day.However,There is no debating the fact that these mysterious den site pictures never seem to actually show up.It would make no sense for a coyote to drag a carcuss back to a den and there's no evidence that they actually do it.Just another urban legend that is as baseless as the broke down cattle trucks loaded with coyotes and the coyotes wit insurance company tags in their ears.