A long time ago they made one specifically for mule deer. At the time I ran the hunting/fishing department for Gart Bros. Sports. They gave me a K'mere Deer mule deer call to try out. It was basically a fawn distress call. It worked very well and would bring in more does than it would scare away. It did not bring bucks in unless they followed the does, which they did quite often. What it was really good for though is stopping a buck after you accidently bump him. Nearly every buck would stop for a few seconds and look back if you blew the call right after they took off. Unfortunately it eventually fell apart and I don't even know if they still make one for mule deer? Do they have a website?
