Carlos Daniel CadenaLaura PabónAndrés Felipe Díaz-SalazarMaria Elisa MendiwelsoNatalia Ocampo-PeñuelaNelsy Niño-RodríguezJuliana Soto-PatiñoGlenn F. SeeholzerSuzette G. A. FlantuaLinelle Abueg2026-03-222026-03-22202610.1093/jhered/esag016https://doi.org/10.1093/jhered/esag016https://andeanlibrary.org/handle/123456789/79824Understanding the demographic history of tropical montane species offers insights into how climate-driven habitat dynamics shape genetic diversity and population structure. The Tourmaline Sunangel (Heliangelus exortis), a hummingbird endemic to the Northern Andes of Colombia and Ecuador, inhabits high-elevation ecosystems that were repeatedly impacted by Pleistocene glacial-interglacial cycles. To enable genomic and evolutionary studies in this system, we generated a high-quality, chromosome-level reference genome using PacBio HiFi long reads and Hi-C scaffolding. The resulting 1.05 Gb assembly has contig and scaffold N50s of 8.4 Mb and 73.9 Mb, respectively, with >94 % BUSCO completeness. Using this reference, we analyzed whole-genome resequencing data from ten individuals collected at a single locality in the Eastern Andes of Colombia and reconstructed demographic history with pairwise sequentially Markovian coalescent models. Our results indicate a pronounced population expansion between ~1 Mya and ~300 kya, likely driven by increased habitat connectivity during glacial periods when highland vegetation was displaced downslope, followed by a decline likely associated with interglacial fragmentation. These trends broadly align with paleoecological records, suggesting that populations of forest-associated species such as H. exortis responded to Pleistocene climatic oscillations, though demographic patterns did not strictly mirror known glacial-interglacial dynamics. This work establishes a foundation for future genomic studies in Andean birds, and highlights the potential of combining genomic and paleoecological data to unravel how biodiversity responds to environmental change.enDemographic historyEcologyCoalescent theoryBiologyPopulationHabitatPhylogeographyBiodiversityGlacial periodPleistocenearticle