Shooting herbivores who wander on your property is not the way to deal with them. If the bison had been breaking down his fences and trampling his property, then all he needed was a camera and a few pics of the animals and the and a quick damage trip to the sheriff’s office.
1. It was 'open range', so it was HIS duty to fence them OUT; not the rancher's to fence them IN.
2. In the early stories, it also stated that the fences were buried in heavy snow.
3. The sheriff had already informed him of his rights and duties in response to his earlier complaints.