Torpor is an important energy saving strategy in some small birds, but it has rarely been studied in natural field conditions. We compared torpor use across 43 wild‐caught individuals of eight hummingbird species across sites with different natural temperature regimes. Most laboratory studies focus on the relationship between metabolic rate and temperature, but our aim was to evaluate what environmental factors most influence hummingbird nighttime energy management under natural conditions. We found that the probability of an individual entering torpor was weakly correlated with mass but unrelated to nighttime temperature and that hummingbirds at both warm, tropical and cooler, temperate sites used torpor. Energy savings in torpor were maximized as ambient temperatures approached a species’ minimum body temperature, consistent with laboratory studies; energy savings ranged between 65 and 92% of energy per hour in torpor compared to normothermy. However, regardless of the degree of energy savings in torpor, variation in total nighttime energy expenditure was most significantly influenced by torpor bout duration. Lab studies largely assess the effect of temperature on torpor use, but our findings indicate that other environmental conditions are more important in determining hummingbirds’ total nighttime energy expenditure under natural temperature cycles. Our results show that a small endotherm's nighttime energy management in its natural habitat is more affected by torpor bout duration, which is linked to photoperiod, than by temperature. This result suggests that in their natural environments hummingbirds are able to save energy in torpor across a range of nighttime temperatures, indicating that they may have sufficient physiological flexibility to tolerate climatic variation.

中文翻译：

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蜂鸟的背景：持续时间，而不是温度，是夜间节能的关键

在某些小型鸟类中，Torpor是重要的节能策略，但很少在自然田间条件下进行研究。我们比较了自然温度不同地区的八种蜂鸟在43个野生捕捞个体中使用的酚。大多数实验室研究都集中在代谢率和温度之间的关系上，但我们的目的是评估在自然条件下最能影响蜂鸟夜间能量管理的环境因素。我们发现，一个人进入火炬的可能性与质量的相关性很弱，但与夜间温度无关，并且在温暖，热带和凉爽，温带地区的蜂鸟都使用火炬。当环境温度接近物种的最低体温时，可以最大程度地节省能源。与实验室研究一致；与常温模式相比，每小时可节省的能源节省了65％至92％。但是，无论在节约能源的程度上，总的夜间能源消耗的变化最显着地受到持续时间的影响。实验室研究在很大程度上评估了温度对使用火炬的影响，但我们的发现表明，其他环境条件对于确定自然温度周期下蜂鸟的夜间总能源消耗更为重要。我们的结果表明，在自然栖息地中，一个小的吸热的夜间能量管理受与光周期有关的热弯持续时间的影响更大，而不是温度的影响。