Difference in habits may be due simply to difference of locality, or to the need of adaptation to new conditions. The prongbuck’s habits about migration offer examples of the former kind of difference. Over portions of its range the prongbuck is not migratory at all. In other parts the migrations are purely local. In yet other regions the migrations are continued for great distances, immense multitudes of the animals going to and fro in the spring and fall along well-beaten tracks. I know of one place in New Mexico where the pronghorn herds are tenants of certain great plains throughout the entire year. I know another region in northwestern Colorado where the very few prongbucks still left, though they shift from valley to valley, yet spend the whole year in the same stretch of rolling, barren country. On the Little Missouri, however, during the eighties and early nineties, there was a very distinct though usually local migration. Before the Black Hills had been settled they were famous wintering places for the antelope, which swarmed from great distances to them when cold weather approached; those which had summered east of the Big Missouri actually swam the river in great herds, on their journey to the Hills. The old hunters around my ranch insisted that formerly the prongbuck had for the most part travelled from the Little Missouri Bad Lands into the Black Hills for the winter. [Illustration: ON THE LITTLE MISSOURI ] When I was ranching on that river, however, this custom no longer obtained, for the Black Hills were too well settled, and the herds of prongbuck that wintered there were steadily diminishing in numbers. At that time, from 1883 to 1896, the seasonal change in habits, and shift of position, of the prongbucks were well marked. As soon as the new grass sprang they appeared in great numbers upon the plains. They were especially fond of the green, tender blades that came up where the country had been burned over. If the region had been devastated by prairie fires in the fall, the next spring it was certain to contain hundreds and thousands of prongbucks. All through the summer they remained out on these great open plains, coming to drink at the little pools in the creek beds, and living where there was no shelter of any kind. As winter approached they began to gather in bands. Some of these bands apparently had regular wintering places to the south of us, in Pretty Buttes and beyond; and close to my ranch, at the crossing of the creek called Beaver, there were certain trails which these antelope regularly travelled, northward in the spring and southward in the fall. But other bands would seek out places in the Bad Lands near by, gathering together on some succession of plateaus which were protected by neighboring hills from the deep drifts of snow. Here they passed the winter, on short commons, it is true (they graze, not browsing like deer), but without danger of perishing in the snowdrifts. On the other