I've always disliked it when tips are just added to your bill, such as is common for larger groups in a restaurant. A gratuity is supposed to be voluntary, and a reward for good service. I have done a number of guided horseback hunting trips, and use 10-15% as the baseline for total gratuities. Although being especially generous to your guide is easy when you scored on an exceptional critter, often times the guide works the hardest for you when the stars don't align and you have an unpunched tag. It's not their fault if the weather socks you in, if you are too out of shape to make it up the mountain, if you miss your shot, etc. On my last hunt in CO, I tipped the guide $100 per day (he was also the cook as we were the only two in camp), the packer who got us in and out of camp $100, and the guy who packed out my bull & took care of the meat, $100.