It must be remembered that wolves limit ungulate numbers by reducing recruitment and increasing adult mortality, not by killing off all the game, instances of surplus killing notwithstanding. In any given year, a number of adult females die from natural causes, disease, or predation. In that same year, a number of calves or fawns are born, but those young also face disease, accidents, and predation, and only a few survive their first year of life to join the adult population. For a stable population, recruitment must balance adult mortality. If recruitment is less, the population declines, and if it is greater, numbers increase.
Predators also kill a few prime age adults.