In September 2007 unusual precipitation patterns created conditions in the eastern steppe of Mongolia (drought conditions in many places and wet conditions in one area) that led to the observation of a historically large Mongolian gazelle Procapra gutturosa herd (> 200,000). A model developed to predict gazelle occurrence based on satellite imagery of vegetation productivity correctly identified the region where the mega-herd was located. Additionally, few gazelles were observed in large portions of adjacent, suitable habitat that either had intense insect activity or were undergoing intensive oil development. Because Mongolian gazelles appear to undertake long-distance nomadic movements to cope with a highly variable environment and food availability, development activities that discourage use of limited suitable habitat may ultimately reduce gazelle fecundity or increase mortality. Landscape level conservation strategies that prevent habitat loss and allow access to all of the grasslands seem preferable to strategies that focus on enhancing a handful of protected areas.