It really depends on the hunt, the value/type of the hunt to be more specific. If you're doing a bull elk hunt in New Mexico, and it's supposed to be a trophy hunt, say 350" of better, and the food and accommodations are first class I'd expect the guide to be expecting a hefty tip. I don't know what trophy bull elk hunts go for in New Mexico these days, but I'd guess some where around $6k to $8K+ for an honest to goodness quality bull.
If it will be field accommodations, I'd personally expect a nicely well set up camp with comfortable cots and wood stoves to keep warm. Shower tent, restroom tent, mess tent. And the meals should be first class also, good breakfast, steaks, chops, stews and the like for dinner. And lots of good beverages and snacks for day packs. A top notch hunt, and if you dropped a nice 350" or better bull, 15%+ is well worth it and shows you appreciate the professionalism of your guide team. This is how my boys and I do it, and most of the guides we know do it like this.
OTOH, if it's a low budget hunt, comfort and meals aren't anything special, I'd tip 10% and leave it at that.
SMOA