Diet of the great horned owl Bubo virginianus nigrescens in an Andean forest remnant, northern Ecuador and a review of the subspecies' dietary patterns

Understanding the feeding ecology of top avian predators is crucial to unravelling trophic interactions and informing conservation strategies. Great Horned Owl Bubo virginianus, although among the most widespread nocturnal raptors in America, remains understudied in the northern Andes. We investigated the diet of the Andean subspecies B. v. nigrescens in an inter-Andean valley of northern Ecuador and compiled a literature review of its dietary patterns across the subspecies' range in Colombia and Ecuador. We analysed 57 pellets (43 complete, 14 fragmented) collected each December from 2014 to 2017. The 106 identified prey items comprised mammals as the primary food source (73 % of items, 94 % of total estimated biomass), with Andean White-eared Opossum Didelphis pernigra (66 % of biomass) and Black Rat Rattus rattus (22 % of biomass) contributing the largest share. Smaller native and introduced rodents were also common (48 % of all items), while other groups appeared less frequently: birds (10 %), frogs (5 %), bats (3 %) and Scarabaeid beetles (12 % by count but ∼0.1 % of biomass), underscoring the owl's generalist foraging. Because our empirical sampling was restricted to a single pair and a single month per year, intra-annual shifts cannot be assessed here and some prey groups may be underrepresented; we therefore interpret patterns conservatively. A new record of predation on a young Domestic Cat Felis catus highlights adaptability to urbanised landscapes. Our literature review revealed seven studies spanning páramo to inter-Andean valleys showing similar trends across Colombia and Ecuador, with mammalian prey—often rabbits in higher elevations—dominant throughout, and highlights geographic gaps (e.g., northern Peru, large portions of Ecuador and Colombia). These findings suggest that B. v. nigrescens exhibits a flexible feeding ecology, capitalising on native and non-native prey. However, shifting land-use practices may affect prey availability and pose future challenges for this apex predator. Coordinated, year-round, multi-elevation studies would clarify seasonal variation and broader ecological dynamics, guiding conservation efforts in tropical mountain ecosystems.