Like all hummingbirds, Peruvian Sheartail feeds on small insects as well as flowers. Nectar from flowers likely provides the bulk of calories. Short bill and small size are adaptations to feed on small low-yield flowers including numerous insect-syndrome flowers. In Chile, readily steals nectar from Tecoma fulva, through holes pierced in the corolla by Cinereous Conebill (Conirostrum cinereum) (Clark et al. 2013). Other flowers visited include chañar (Geoffroea decorticans), Trixis cacalioides, Pluchea chingoyo (Clark et al. 2013), Leonotis sp., Vicia faba, Eucalyptus sp., Lantana camara, and Ricinus communis (van Dongen et al. 2013). Arthropods caught on the wing in typical hummingbird fashion, with perched bird suddenly sallying to catch one or more tiny flying insects.
Feces are primarily of excess water acquired from nectar, and dark hard pellets of arthropod exoskeleton.