The only way to test the impact of hunting is to simply not do it and observe the results. Has that been done?
I'm not condemning hunting, I could GAF what all you kill or why. People pay bags of $ to kill pen raised pheasant. I find that nothing less than inane! but I cannot work up any objection. Rationalizing hunting in the 21stCentury beyond some game management issues is ridiculous. Are the grouse overburdening their habitat? A threat to human populations?
Please, spare me. Kill what you want, glory in the boldness of the hunt, and eat whatever is left after the blasting in good health.