American bison were reduced from 30 million to fewer than 1,000 by the late 19th century, and their ongoing restoration to grassland ecosystems benefits both the species and the biodiversity of the landscapes they shaped.
Bison welfare in conservation settings involves managing animals adapted to continent-scale migration within necessarily bounded reserves. Insufficient range creates overgrazing that depletes the grass diversity bison require, causing nutritional stress. Social disruption from population management culls or relocations creates stress in the tight social bonds of bison groups. Fencing prevents migration to better-quality pasture during drought, forcing animals to remain in poor conditions. Conservation herd management that maintains genetic diversity, adequate range, and social cohesion simultaneously addresses population and welfare goals. The scale of the historical loss — tens of millions of animals killed within decades — remains one of the largest wildlife welfare events in recorded history.