This examination of a depopulated species, the North American bison, provides insights into the past and present behaviour and ecology of what was once the continent's largest terrestrial mammal. The authors' research, conducted over a five-year period, attempts to resolve such questions as: what happens when only a small proportion of the male of a species mate?; why do animals in particular areas experience morphological malformations?; and how much genetic diversity has been lost since the 19th century? The study also discusses the consequences of mating failures, lineage differences in growth and birth synchrony. It explores behavioural ecology, mate choice, the conservation of ecosystems and the management of endangered species.