The species inhabits small remnant patches of native scrub in desert river valleys up to 750 m, but birds are occasionally reported above 2,000 m and once as high as 3,000 m (J. Fjeldså in litt. 1999, C. F. Estades in litt. 2007). It migrates altitudinally and may require fairly continuous vegetation along rivers to undertake such movements (Howell and Webb 1995). Estades et al. (2007) observed woodstars feeding on the flowers of native trees like the chañar (Geoffroea decorticans) and pimiento (Schinus molle), as well as ornamentals like Lantana camara, Pelargonium spp. and Bougainvillea sp. and crop plants such as alfalfa (Medicago sativa), garlic, onion (Allium spp.), and tomato (Lycopersicon esculentum). They noted that the favoured species have entomophyllous flowers rather than typical ornithophyllous flowers (Estades et al. 2007). The species has often been reported feeding in gardens, particularly on Lantana and Hibiscus flowers (Fjeldså and Krabbe 1990), but it is comparatively rare in such habitats (Howell and Webb 1995). It uses fruit groves for feeding (Citrus spp.) and nesting (olive trees) (C. Estades in litt. 2007). Despite the large numbers formerly seen feeding in flowering trees, it is usually a solitary feeder. Active nests have been found in April, May, late August and September and there appear to be two annual peaks in breeding activity (C. F. Estades in litt. 2007, Estades et al. 2007). It is likely that males display at leks. Courtship territories are placed above dense thickets which are now scarce in Azapa and Vítor (Clark et al. 2013).

Eulidia yarrellii is only known to breed regularly in the Azapa, Chaca (Vítor) and Camarones valleys, Arica department, extreme northern Chile (C. F. Estades in litt. 2007, A. Jaramillo in litt. 2014). Stragglers have been found north to Tacna and possibly Moquegua departments, southern Peru, and there is a historical record as far south as northern Antofagasta province; yet, there are no recent records for Peru (C. F. Estades in litt. 2007). Monthly searches for the species in all Tacna valleys (southern Peru) during 2008-2009 did not yield any records of this species (N. Hidalgo in litt. 2013).

Conservation Actions Underway
CITES Appendix II. All exports of hummingbirds from Peru and Chile are controlled. A ten-year species recovery plan was approved in 2004 and included plans for a public awareness campaign, a study of competition between the woodstar and Peruvian Sheartail, a permanent population monitoring programme, restoration of natural vegetation in the Azapa and Lluta valleys, incorporation of its conservation into the agenda of the local Good Agricultural Practices committee, and a study of the feasibility of an ex-situ conservation project and reintroduction into suitable areas within the historical range (C. F. Estades in litt. 2007, Estades et al. 2007). Attempts have been made to provide artificial feeders for the species; however, it proved reluctant to use them and other hummingbird species displaced E. yarrellii through their monopolisation of the new resource (P. L. Gonzalez-Gomez in litt. 2014). There are plans to create a network of small reserves to protect the habitat used by the species for lekking and breeding; two small reserves have now been created: the Chaca Biologic Station in the Valley of Vítor and El Rapido Biologic Station in the Azapa Valley (Lebbin 2013, Yañez 2016, Almendras undated). Trial habitat restoration at a site in the Chaca valley was successful, with the species using the restored habitat for breeding (Yañez 2016). Some work has been undertaken to raise awareness of the species's conservation among the public, particularly in schools (Yañez 2016). A "Ruta del Picaflor de Arica" has recently been established (Sepúlveda 2020).

Conservation Actions Proposed
Research the genetic structure of the populations. Carry out habitat restoration in the Lluta, Chaca and Azapa valleys, ensuring that species whose flowers are visited regularly by E. yarrellii are planted (P. L. Gonzalez-Gomez in litt. 2014). Continue population monitoring, as detailed in the species recovery plan. Limit the amount of pesticides used in Azapa and Chaca valleys. Investigate the effects of territorial interactions between Chilean Woodstar and Peruvian Sheartail (Clark et al. 2013). Scale-up work to raise awareness of the species among the general public (Yañez 2016). Continue with the planning of a network of small reserves to protect the habitat used by the species.