Animals living at high altitudes are challenged by the extreme environmental conditions of cold temperature and hypobaric hypoxia. It is not well understood how high-altitude birds enhance the capacity of metabolic thermogenesis and allocate metabolic capacity in different organs to maximize survival in extreme conditions of a cold winter. The Qinghai-Tibet Plateau (QTP) is the largest and highest plateau globally, offering a natural laboratory for investigating coping mechanisms of organisms inhabiting extreme environments. To understand the adaptive strategies in the morphology and physiology of small songbirds on the QTP, we compared plasma triiodothyronine (T₃), pectoralis muscle mitochondrial cytochrome c oxidase (COX) and state IV capacities, the expression of peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), adenine nucleotide translocase (ANT), uncoupling protein (UCP), and adenosine monophosphate‐dependent kinase (AMPK) α1 mRNA in the pectoralis and liver of Eurasian tree sparrows (Passer montanus) from high-altitude (3,230 m), medium-altitude (1400 m), and low-altitude (80 m) regions. Our results showed that high-altitude sparrows had greater body masses, longer wings and tarsometatarsi, but comparable bill lengths relative to medium- and low-altitude individuals. High-altitude sparrows had higher plasma T₃ levels and pectoralis muscle mitochondrial COX capacities than their lowland counterparts. They also upregulated the pectoralis muscle mRNA expression of UCP, PGC-1α, and ANT proteins relative to low-altitude sparrows. Unlike pectoralis, high-altitude sparrows significantly down-regulated hepatic AMPKα1 and ANT protein expression as compared with their lowland counterparts. Our results contribute to understanding the morphological, biochemical, and molecular adaptations in free-living birds to cope with the cold seasons in the extreme environment of the QTP.

生活在高海拔地区的动物受到低温和低压缺氧的极端环境条件的挑战。目前尚不清楚高海拔鸟类如何提高代谢产热能力并在不同器官中分配代谢能力以最大限度地提高寒冷冬季极端条件下的生存率。青藏高原（QTP）是全球最大、海拔最高的高原，是研究极端环境生物应对机制的天然实验室。为了了解 QTP 上小型鸣禽形态和生理的适应性策略，我们比较了血浆三碘甲状腺原氨酸 (T ₃ )、胸大肌线粒体细胞色素c氧化酶 (COX) 和 IV 状态能力、过氧化物酶体增殖物激活受体 γ 共激活因子 α (PGC-1α)、腺嘌呤核苷酸转位酶 (ANT)、解偶联蛋白 (UCP) 和单磷酸腺苷依赖性激酶 (AMPK) α1 mRNA 的表达在高海拔 (3,230 m)、中海拔 (1400 m) 和低海拔 (80 m) 地区的欧亚麻雀 ( Passer montanus ) 的胸大肌和肝脏中。我们的研究结果表明，高海拔麻雀的体重更大，翅膀和跗跖骨更长，但与中低海拔个体相比，喙的长度相当。高海拔麻雀血浆T _3较高水平和胸大肌线粒体 COX 能力比低地对应物。相对于低海拔麻雀，它们还上调了 UCP、PGC-1α 和 ANT 蛋白的胸肌 mRNA 表达。与胸大肌不同，与低地麻雀相比，高海拔麻雀显着下调肝脏 AMPKα1 和 ANT 蛋白表达。我们的研究结果有助于了解自由生活鸟类的形态、生化和分子适应，以应对青藏高原极端环境中的寒冷季节。