It inhabits cloud-forest, evergreen subtropical and semi-humid forest, forest edge and adjacent coffee fincas at elevations of 800-2,440 m (Howell and Webb 1995). It is probably marginal or seasonal at the lower altitudes (below 1,200 m) in the ecotone between tropical semi-deciduous forest and cloud-forest. The species requires intact, pristine forest (Arizmendi et al. 2020). It feeds on a variety of flowering plants, but is subordinate to other hummingbirds in its range (T. Züchner in litt. 1999). Breeding season peaks are likely to be February-May and September-October (Arizmendi et al. 2020).

Eupherusa poliocerca is fairly common to common (Howell and Webb 1995; M. Reid in litt. 1998) but extremely local on the Pacific slope of the Sierra Madre del Sur in Guerrero and west Oaxaca, south-west Mexico. Most records in Guerrero are from near Omiltemi and along the Atoyac de Alvarez-Teotepec road (e.g., Navarro 1992), but it has been recorded further west, inland from Zihuatanejo. The species requires montane forests, which cover a total area of 5,600 km² within the range (Global Forest Watch 2021).

Conservation Actions Underway
CITES Appendix II. This species is on the watch list as part of the State of North America's Birds (North American Bird Conservation Initiative 2016).

Conservation Actions Proposed
Carry out surveys to obtain a population estimate and clarify its distribution and the extent of remaining habitat. Designate protected areas throughout its range, particularly in the Sierra de Atoyac (Hernández-Baños et al. 1995; Arizmendi et al. 2016) encompassing the range of this species. Protect remaining habitat.