Torpor is thought to be particularly important for small endotherms occupying cold environments and with limited fat reserves to fuel metabolism, yet among birds deep torpor is both rare and variable in extent. We investigated torpor in hummingbirds at approximately 3800 m.a.s.l. in the tropical Andes by monitoring body temperature (T_b) in 26 individuals of six species held captive overnight and experiencing natural air temperature (T_a) patterns. All species used pronounced torpor, with one Metallura phoebe reaching a minimum T_b of 3.26°C, the lowest yet reported for any bird or non-hibernating mammal. The extent and duration of torpor varied among species, with overnight body mass (M_b) loss negatively correlated with both minimum T_b and bout duration. We found a significant phylogenetic signal for minimum T_b and overnight M_b loss, consistent with evolutionarily conserved thermoregulatory traits. Our findings suggest deep torpor is routine for high Andean hummingbirds, but evolved species differences affect its depth.

人们认为，对于生活在寒冷环境中且燃料代谢所需的脂肪储备有限的小型恒温动物来说，麻木状态尤其重要，但在鸟类中，深度麻木现象非常罕见，而且程度各异。我们通过监测过夜圈养的 6 个物种的 26 只蜂鸟的体温 ( T _b ) 并体验自然气温 ( T _a ) 模式，研究了热带安第斯山脉大约 3800 米的蜂鸟的麻木状态。所有物种都表现出明显的冬眠状态，其中一种金属楠的最低T _b达到 3.26°C，这是迄今为止报道的所有鸟类或非冬眠哺乳动物中的最低温度。不同物种的麻木程度和持续时间各不相同，夜间体重 ( M _b ) 损失与最小T _b和发作持续时间呈负相关。我们发现了最小T _b和隔夜M _b损失的显着系统发育信号，与进化上保守的体温调节特征一致。我们的研究结果表明，深度麻木对于高海拔安第斯蜂鸟来说是很常见的，但进化的物种差异会影响其深度。