Sample Collection.
We collected 140 house wren specimens from a range of elevations (120–4,454 m above sea level) in the Peruvian Andes and adjacent lowlands. All specimens were preserved as vouchers in the ornithological collection of the Museum of Southwestern Biology of the University of New Mexico and the Centro de Ornitología y Biodiversidad (CORBIDI) (Lima, Peru).
All birds were live-trapped in mist nets and were sacrificed in accordance with protocols approved by the University of New Mexico Institutional Care and Use Committee (Protocol 08UNM033-TR-100117; Animal Welfare Assurance number A4023-01). All collections were authorized by permits issued by management authorities of Peru (004-2007-INRENA-IFFS-DCB, 135-2009-AG-DGFFS-DGEFFS, 0377-2010-AG-DGFFS-DGEFFS, 0199-2012-AG-DGFFS-DGEFFS, and 006-2013-MINAGRI-DGFFS/DGEFFS). For each of the 140 house wren specimens, we collected 20–60μL of whole blood from the brachial or ulnar vein using heparinized microcapillary tubes. Red blood cells were separated from the plasma fraction by centrifugation, and the packed red cells were flash-frozen in liquid nitrogen. We collected liver and pectoral muscle from each specimen as sources of genomic DNA and globin mRNA, respectively. Muscle samples were flash-frozen or preserved using RNAlater. All tissue and blood samples were subsequently stored at −80 °C.