Department of Biology, Section for Evolutionary Ecology, Lund University, Lund, Sweden.
J Comp Physiol B. 2020 May;190(3):349-359. doi: 10.1007/s00360-020-01266-5. Epub 2020 Feb 24.
Spending the winter in northern climes with short days and cold ambient temperatures (T) can be energetically challenging for small birds that have high metabolic and heat loss rates. Hence, maintaining body temperature (T) in T below thermoneutrality can be energetically costly for a small bird. We still know little about how increased heat production below thermoneutrality affects the level at which T is maintained, and if these patterns are age specific. To test this, we measured subcutaneous body temperature (T) and resting metabolic rate (RMR) simultaneously in blue tits (Cyanistes caeruleus) during winter nights in T's ranging from 25 to - 15 °C. RMR increased below the lower critical temperature (LCT, estimated at 14 °C) and was 6% higher in young (birds in their first winter) compared to old birds (birds in their second winter or older). The higher RMR was also mirrored in higher T and thermal conductance (C) in young birds, which we suggest could be caused by age differences in plumage quality, likely driven by time constraints during moult. Reduction in nightly predicted T was modest and increased again at the coldest ambient temperatures, suggesting that either heat retention or heat production (or both) improved when T reached levels which are cold by the standards of birds in our population. Our results show that levels of heat production and T can be age specific. Further studies should address age-specific differences on quality, structure, and thermal conductivity of plumage more explicitly, to investigate the role of variation in insulation in age-linked metabolic phenotypes.
在北方寒冷的气候中度过冬季，白天短暂，环境温度（T）低，这对新陈代谢率和热量散失率高的小鸟来说是极具挑战性的。因此，对于小鸟来说，在低于热中性区的 T 下维持体温（T）可能会消耗大量能量。我们仍然不太了解增加热中性区以下的产热量如何影响 T 的维持水平，以及这些模式是否具有年龄特异性。为了检验这一点，我们在 T 从 25 到-15°C 的范围内，同时测量了蓝山雀（Cyanistes caeruleus）在冬季夜间的皮下体温（T）和静息代谢率（RMR）。RMR 在低于下临界温度（LCT，估计为 14°C）时增加，并且在年轻（第一年的小鸟）鸟类中比老年（第二年或更老的鸟类）鸟类高 6%。年轻鸟类的 RMR 也反映在更高的 T 和热传导率（C）上，我们认为这可能是由于羽毛质量的年龄差异造成的，这可能是由于换羽期间的时间限制所致。夜间预测 T 的减少幅度适中，在环境温度最低时再次增加，这表明当 T 达到我们种群中鸟类认为寒冷的水平时，要么是热保留要么是产热（或两者兼有）得到了改善。我们的研究结果表明，产热和 T 的水平可能具有年龄特异性。进一步的研究应该更明确地探讨羽毛质量、结构和热导率的年龄特异性差异，以研究隔热变异在与年龄相关的代谢表型中的作用。
