We explored how climate change during the last ~ 21,000 years may have affected the distribution and demography of the Plumbeous Sierra-finch (Geospizopsis unicolor) across the Ecuadorian paramos. Also, given the current island-like configuration of this ecosystem, we attempted to identify areas that may hold genetically isolated populations, as well as the potential geographic-ecological barriers causing such isolation. To this end, we used paleoclimatic modeling and a series of population genetic analyses based on two mitochondrial markers. Our models show an expansion of the potential distribution of the species during the Last Glacial Maximum (LGM) compared to the current potential distribution, and the genetic data show signals of population expansion loosely around the LGM. Our results depict a picture of relatively low genetic structure of the Plumbeous Sierra-finch along the paramos of Ecuador, but there is evidence of potential isolation of populations in the paramos of Galeras-Chiles (northern Ecuador).