Filling distributional gaps for birds in a complex Andean landscape: insights from the northern East Andes of Colombia

The East Andes of Colombia is a biogeographically complex region with significant avian diversity and endemism. Despite previous efforts, large portions of its northern sector remain unexplored ornithologically. We report new distributional data for 38 bird species at 42 localities in Santander and Norte de Santander departments, spanning elevations from 825 m to 3,700 m. These records bridge notable distributional gaps for several Andean species and expand known ranges northward, particularly in montane forest ecosystems. Among others, we report range extensions for Solitary Eagle Buteogallus solitarius, Chapman's Swift Chaetura chapmani, Cinnamon Screech Owl Megascops petersoni, Yellow-throated Spadebill Platyrinchus flavigularis and Sooty Grassquit Asemospiza fuliginosa, as well as the first specimen records for Colombia of Streak-capped Treehunter Thripadectes virgaticeps tachirensis and Russet Antshrike Thamnistes anabatinus gularis. The results underscore the role of geographic barriers, such as arid river canyons and high elevations in shaping avian distributions, leading to disjunct populations and potential zones of secondary contact. Our study emphasises the value of combining historical data, modern observations and specimen collection to clarify species distributions, taxonomy and evolutionary patterns. It also stresses the need for rigorous field documentation, including detailed locality descriptions and habitat notes, to improve data quality and their long-term utility. Continued exploration of understudied areas, such as the east slope of the Sierra Nevada del Cocuy and fragmented foothill forests, is essential to uncover additional biodiversity and to inform conservation efforts.