A heterothermic spectrum in hummingbirds

Many small endotherms use torpor, saving energy by a controlled reduction of their body temperature and metabolic rate. Some species (e.g. arctic ground squirrels, hummingbirds) enter deep torpor, dropping their body temperatures by 23-37 &[deg]C, while others can only enter shallow torpor (e.g., pigeons, 3-10 &[deg]C reductions). However, deep torpor in mammals can increase predation risk (unless animals are in burrows or caves), inhibit immune function, and result in sleep deprivation, so even for species that can enter deep torpor, facultative shallow torpor might help balance energy savings with these potential costs. Deep torpor occurs in three avian orders. Although the literature hints that some bird species can use both shallow and deep torpor, little empirical evidence of such an avian torpor spectrum exists. We infrared imaged three hummingbird species that are known to use deep torpor, under natural temperature and light cycles, to test if they were also capable of sh...许多小型内温动物（endotherms）会通过可控降低体温与代谢速率来节省能量，即蛰伏（torpor）行为。部分物种（如北极地松鼠、蜂鸟）可进入深度蛰伏，体温降幅可达23至37摄氏度；而另有部分物种仅能进入浅度蛰伏（如鸽子，体温降幅为3至10摄氏度）。然而，哺乳动物的深度蛰伏会提升被捕食风险（除非动物身处洞穴或岩窟中）、抑制免疫功能，并引发睡眠剥夺；因此即便对于能够进入深度蛰伏的物种而言，兼性浅度蛰伏（facultative shallow torpor）或许能够在能量节省与上述潜在代价之间达成平衡。深度蛰伏现象存在于三个鸟类目类群（avian orders）中。尽管已有文献暗示部分鸟类物种能够同时利用浅度与深度蛰伏，但针对这类鸟类蛰伏谱系的实证研究证据仍极为匮乏。我们在自然温度与光照周期条件下，对三种已知可进行深度蛰伏的蜂鸟物种开展红外成像监测，以验证它们是否同样具备……