Black-breasted Pufflegs (Eriocnemis nigrivestis) are hummingbirds endemic to Ecuador and are considered critically endangered because of their limited distribution, a population estimated at fewer than 1000 individuals, and ongoing habitat degradation. From November 2013 to June 2016, we examined the foraging preferences of these hummingbirds using a combination of direct observations, time-lapse cameras, and motion-detection software. We first identified 21 species of ornithophilous plants distributed among five sites in the northwestern flanks of the Pichincha volcano in northwest Ecuador. We then monitored these plant species using time-lapse cameras and recorded 144 visits by Black-breasted Pufflegs to seven of the 21 species. Most visits (128 of 144 visits, 89%) were to just two species of plants, Macleania rupestris and Palicourea fuchsioides, the latter of which is also an endemic and threatened species. In addition, Black-breasted Pufflegs were only observed in the most pristine habitats. Given the potential negative effects of climate change for species in the tropical Andes plus the possible loss and degradation of habitat resulting from human activities, efforts are needed to conserve habitats currently used by Black-breasted Pufflegs, recover degraded habitats, and connect isolated patches of suitable habitat. Our results concerning species of flowering plants used most by Black-breasted Pufflegs (P. fuchsioides and M. rupestris) should help guide any habitat restoration initiatives.