Yes, it is normal behavior. I've seen buffalo in Custer State Park, in the Black Hills of South Dakota, where they have a large enough range that they can follow their natural instincts, and I learned that buffalo herds usually consist of only cows and young. Adult bulls join the herd only during mating season, and otherwise are loners. There are "wild" buffalo herds also in the Badlands National Park, SD, and in Yellowstone. There may be others.