Traditional pastoralism is a significant contributor to African economies but is, as yet, little understood. Ngorongoro Conservation Area (NCA) provides a microcosm illustrating pastoralism under a range of ecological conditions. Herd declines found across a range of NCA study sites are illustrated in detail with respect to events in one representative study site monitored for 25 months. A 52% decline in cattle numbers during this period is attributed to quantified factors of low calving rates and high adult and calf mortality attributed to drought and its interaction with high incidence of disease. Human subsistence was directly affected over the same period by a 75% decline in numbers of lactating cows per household. This case illustrates events occurring in herds across NCA. Suggested major causes are breakdown of water and acaricide supplies, as well as severe drought.