The Tibetan fox (Vulpes ferrilata) is generally acknowledged to be a specialist forager on its preferred prey, the burrowing lagomorph plateau pika (Ochotona curzoniae), but whether true dependency characterizes the relationship remains unclear. We estimated the presence of Tibetan foxes in 62 habitat patches that reflected a continuum of environmental conditions within their known geographic distribution within Qinghai Province, China. We used site-occupancy modeling and quantified the abundance of plateau pikas as well as other site variables that could plausibly predict fox presence. We quantified fox presence by collecting and sequencing DNA from scats. The number of pikas and the number of their burrows were the only covariates supported in predictive models of Tibetan fox presence. The probability of site occupancy by foxes increased with pika abundance, and was close to 0 when pikas were absent even within habitat patches otherwise generally suitable. DNA-based diet analysis also allowed us to identify prey species consumed by Tibetan foxes. Approximately 99% of fox scats contained pika DNA sequences, 97% contained predominantly pika sequences, and 73% contained only pika sequences. We conclude that Tibetan foxes in this region are not merely foraging specialists of plateau pikas, but that they are obligate predators on pikas. Plateau pikas, while presently still abundant on the Qinghai-Tibetan Plateau, are considered a pest by government policy and are subject to extensive, government-funded poisoning programs. The Tibetan fox is currently at no substantial risk as a species, but this could change if pika poisoning increases in scope, intensity, or effectiveness.