Background/Question/Methods Prairie dogs (Cynomys spp.) are burrowing rodents considered to be ecosystem engineers and keystone species of the central grasslands of North America. Yet, prairie dog populations have declined by an estimated 98% throughout their historic range. This dramatic decline has resulted in the widespread loss of their important ecological role throughout this grassland system. The 92,060 ha Sevilleta National Wildlife Refuge (SNWR), in central New Mexico includes more than 54,000 ha of native grassland. Gunnison’s prairie dogs (C. gunnisoni) were reported to occupy ~15,000 ha of the SNWR during the 1960’s, prior to the establishment of the refuge and the systematic eradication of prairie dogs. In 2005, we collaborated with local agencies and conservation organizations to restore the functional role of prairie dogs to the grassland system. Gunnison’s prairie dogs were reintroduced to a 50 ha site that was occupied by prairie dogs 40 years ago. To follow their recolonization of the landscape, we mapped active mounds over time. This work is part of a larger, long-term study where we are studying the ecological effects of prairie dogs as they re-colonize the grassland ecosystem. Results/Conclusions We released 362 individuals in summer 2005, resulting in the establishment of 423 active mounds by fall 2006. Drought and evidence of severe predation prompted the release of 317 additional prairie dogs in summer 2007, resulting in 435 active burrows mapped by fall of that year. During spring 2008, population augmentation was continued, adding 225 more individuals. We found that predation and drought, especially during the spring, dramatically affected the success of our reintroductions. Managers must consider that a recently released prairie dog population provides a tiny island of high density prey, ideal for predators, and that spring drought and winter predation can have particularly large impacts on hibernating species of prairie dogs, like the Gunnison’s. Our work demonstrates that establishing a viable prairie dog colony requires the release of a large number of prairie dogs over time until their burrows and populations are well-established enough to withstand predation and environmental variation. Such work also reinforces the importance of maintaining existing prairie dog colonies in natural areas, and that relocations, while important, are only one part of the conservation solution.