Only hunters know the difference between a jack, cottontail or snowshoe... as far as the coyotes are concerned they are all generally something to eat... where we hunt we prefer jack calls too and there are NO jacks and never have been... it is probaly a pitch thing as far as them hearing and responding to it. I also believe that the yotes mood and how lively the squalling critter sounds will determine if they bother to chase it... wild creatures know if they are going to burn more calories chasing something than they will get from eating it... if it seems like an EASY meal, they will go for it, as long as your set up is good and they don't bust you.