—Nesting density of Saker Falcons (Falco cherrug) in some regions of Mongolia were found to fluctuate dramatically over the years. Very few eyries were consistently occupied year after year. These observations suggest that many Sakers leave one territory, move long distances, and establish new territories. The most likely explanation for this nomadism is instability of food sources (i.e., regional peaks and valleys in populations of small rodents). Other demographic traits suggesting nomadism include the mid-summer absence of adults in territories occupied earlier in the spring, asynchronous breeding (i.e., a high proportion of late clutches), abandonment of eggs, more frequent use of marginal sites (e.g., ground nests) in zones of high prey density, and, in the long term, low occupancy rates of poor sites. The data for Mongolia suggest that the Saker Falcon exhibits partial nomadism when local prey populations fluctuate widely. More severe fluctuations in prey density in Australia favor complete nomadism for some subpopulations of the Black Falcon (F. subniger). Wide scale prey crashes and the persistence of alternate prey in the Arctic seldom favor nomadism in the Gyrfalcon (F. rusticolus). However, the effects of global warming on Gyrfalcon prey are likely to promote nomadism in the future. Received 24 February 2011, accepted 28 June 2011. ELLIS, D. H., I. KITOWSKI, AND T. B. ROUNDY. 2011. Nomadism in large falcons: Lessons from the Saker Falcon in Mongolia. Pages 291–306 in R. T. Watson, T. J. Cade, M. Fuller, G. Hunt, and E. Potapov (Eds.). Gyrfalcons and Ptarmigan in a Changing World, Volume II. The Peregrine Fund, Boise, Idaho, USA. http://dx.doi.org/10.4080/gpcw.2011.0307