It inhabits cloud-forest at 2,000-3,500 m in Guatemala, with exceptional low-elevation records down to 1,200-1,500 m (Escobar-Ortíz 1997, K. Eisermann in litt. 2012), and 1,400-2,700 m in Mexico. The lack of records from June-August at El Triunfo suggests that it may undertake some altitudinal migration (Gómez de Silva et al. 1999). Breeding generally occurs in January-June, when two eggs are laid (González-García 1995). At Volcán Atitlán, a bird was found incubating in January 2005 on a nest that was apparently later predated, however an adult and immature were seen together there in November 2005 and January 2006. In November 2005, the immature bird was aged at 6-7 months, suggesting that hatching took place between early April and early May (Eisermann et al. 2007). At Volcán Tolimán two nests were found in March and April (Méndez 2010). Its diet comprises fruit, flowers and leaves (González-García 1994, 2005, Cóbar Carranza 2006, F. González-García in litt. 2007, Quiñonez  2010, González-García et al. 2017) and rarely invertebrates (González-García 1994).

Oreophasis derbianus occurs in the Sierra Madre de Chiapas, Mexico, and throughout west-central Guatemala. In Mexico, there are recent records from El Triunfo, Cerro Venado, Cerro Cebu, Cerro Quetzal and Volcán Tacaná (Cerro Toquián Grande, Chiquihuite, Agua Caliente, Benito Juárez El Plan), and birds have been purportedly collected, and a tail feather found, in the Chimalapas area of Oaxaca (J. Estudillo López in litt. 1994, González-García 1997, F. González-García in litt. 2012). Its occurrence in the Chimalapas, Oaxaca zone, has always been suspected, but never completely confirmed (F. González-García in litt. 2007). Fieldwork in 2005 and interviews with local people at San Antonio and Benito Juarez in the municipalities of San Miguel and Santa María, Chimalapas, suggest the presence of the species (F. González-García in litt. 2007). Verbal evidence suggests the Horned Guan is present in the areas known as Cordón El Retén y Sierra Tres Picos (González-García and Santana Castellón 2006). In Guatemala, it has been reported in at least 39 localities and its range has been estimated at 1,139.4 km² (Rivas Romero and Cóbar Carranza 2007). The most recent Guatemalan records are from Cerro Cruz Maltín, Huehuetenango (Cotí 2010) and Chuamazán, Totonicapán (J. L. López per A. J. Cobar in litt. 2012). It was found nesting at Volcán Atitlán in 2005, 2007 and 2011 (Eisermann et al. 2007, Eisermann in litt. 2012) and at Volcan Tolimán in 2000 (Méndez 2010). In September 2007, two juveniles were observed at Volcán San Pedro, and in August 2009, another two juveniles were observed in Albores, Sierra de las Minas, confirming breeding at both sites (J. Rivas in litt. 2007, Quiñonez 2010). Fieldwork and interviews have recently identified new localities, including San Marcos and Sibinal in San Marcos department, and Chiantla and Santa Eulalia in Huehuetenango department (Cóbar Carranza and Rivas Romero 2006). Local people report the species from Cerro Tecpán, Chimaltenango, and Cerro El Amay, Quiché (K. Eisermann in litt. 2007), although specific surveys at the latter in 2008, 2010 and 2011 failed to find the species (Tanimoto 2008, P. Tanimoto in litt. 2008, Eisermann and Avendaño 2011, González Madrid 2011, K.  Eisermann in litt. 2012). There are unconfirmed reports from Cerro Volcán Pacayita, Honduras. Unsuccessful searches for the species and interviews with local people in El Trifinio protected area suggest it is absent from this region and does not occur in Honduras (J. Rivas in litt. 2007). Numbers decreased severely during the 20th century and nowhere is it better than uncommon.

Conservation Actions Underway
CITES Appendix I and legally protected in Mexico and Guatemala. In 2010 Mexico named the Horned Guan a one of the Conservation Priority Species (SEMARNAT 2011). An detailed conservation action plan for the species has been drawn up by the Mexican federal government (SEMARNAT 2011). An environmental education programme around El Triunfo has been in progress since 2010 (F. González-García in litt. 2012). The issues covered include strengthening local participation actions in the conservation of the Horned Guan, pasture management for local cattle ranchers and sustainable harvesting of dwarf 'shate' palm (F. González-García in litt. 2012). Another project at El Triunfo is concerned with the production of shade-grown coffee. Many coffee farmers are signing up for organic certification, with almost 121.4 km² (30,000 acres) within the reserve certified by 2004 (Streiffert 2004). In Guatemala, most sites with recent records have protected status (K. Eisermann in litt. 2007). However, deficiencies in management that allow illegal hunting and illegal logging within protected areas are a serious issue for the species's conservation (K. Eisermann in litt. 2007). It has also been stated that there may not be enough suitable habitat incorporated in the national system of protected areas in Guatemala to ensure its survival in these reserves (Cóbar Carranza and Rivas Romero 2006). In Guatemala, communities at Sibinal, San Marcos (Department of San Marcos) and Tecpán (Department of Chimaltenango), at known sites for the species, have formally designated their forests as Municipal Protected Areas (A. J. Cóbar Carranza in litt. 2007), and at least one of these has a reforestation programme. In Guatemala, Cerro Yaxcalamte, Cerro Cruz Maltín, Municipal Forest of San Marcos and Volcán de Tajumulco have been identified as potential areas for further studies and conservation measures (Cóbar Carranza and Rivas Romero 2006). Horned Guan is a 'flagship species' for the development of local tourism at several sites in Guatemala, fostering local interest and initiatives to protect guan habitat, at Atitlán volcano, San Pedro volcano, and in Sibinal (K. Eisermann in litt. 2007, 2012). In 2002 a Population and Habitat Viability Analysis of the Horned Guan was held in Guatemala. This resulted in an action plan (CBSG 2002) and the establishment of the International Committee for the Conservation of Oreophasis derbianus and its Habitat, which is active in Mexico and Guatemala, and has organised four symposiums in which advances in conservation have been presented and the action plan reviewed (Secaira et al. 2006, J. Rivas in litt. 2007, J. Cornejo in litt. 2012). The Cloud Ambassadors Program was established in 2007 by Africam Safari to support in situ conservation efforts and create an international ex situ conservation network via the loaning of captive bred animals from Mexico (Cornejo 2008). The program manages a fund to support in situ conservation projects (J. Cornejo in litt. 2012). The captive husbandry of the species has improved in the last years (Cornejo 2008, 2009). According to the international studbook of the species, at the end of 2010 the captive population  numbered 88 individuals, held by eleven institutions in six countries (J. Cornejo in litt. 2012).

Conservation Actions Proposed
Conduct surveys to obtain an estimate of local population densities and the total population size. Survey potential sites, especially in the Chimalapas area (F. González-García in litt. 1998, 1999) and Honduras. Study the species's movements and role in seed dispersal (F. González-García in litt. 2007). Conduct further research and conservation action in key areas in Guatemala (Cóbar Carranza and Rivas Romero 2006). In Guatemala, identify areas where reforestation with native species can be carried out (Cóbar Carranza and Rivas Romero 2006). Monitor local populations. Monitor rates of cloud-forest destruction and degradation in the species's range. Attempt to quantify the levels of hunting and trapping of this species. Create an international reserve at Volcán Tacaná. Enforce existing laws. Collar and Butchart (2013) suggest that captive breeding should be considered. Carry out research into its breeding biology using captive birds (Eisermann et al. 2007). Assess the impact of ecotourism on the species and its habitat (K. Eisermann in litt. 2007). Improve the managment of existing protected areas across the species's range. Designate further areas at keys sites and ensure effective management (A. J. Cóbar Carranza in litt. 2007).