来源：《新科学家》
原文刊登日期：2021年11月12日
Tropical birds deep in Brazil’s Amazon rainforest are shrinking and developing longer wings as they adapt to climate change.
巴西亚马逊河雨林深处的热带鸟类在适应气候变化的过程中正在变小并长出更长的翅膀。
Researchers studied data for 77 tropical bird species over the past 40 years and found that all of them had lost body mass, with some species losing nearly 2 per cent of their weight per decade. A third of the species studied also developed longer wings.
研究人员研究了过去40年里77种热带鸟类的数据，发现它们的体重都在下降，有些物种每10年体重就会下降近2%。三分之一的被研究物种也长出了更长的翅膀。
A landmark 2019 study of birds that had crashed into buildings in Chicago, Illinois, found that they had lost mass and gained wingspan over a 40-year period, but those species were migratory. To see whether seasonal migration, the birds gradually shifting latitude or the direct effects of human activity had been driving the change, researchers examined the records of 15,000 non-migratory birds inhabiting an unspoiled rainforest in north-west Brazil.
2019年，一项里程碑式的研究发现，在伊利诺伊州芝加哥，撞到建筑物的鸟类在40年的时间里体重下降，翼展增加，但这些物种是候鸟。为了弄清究竟是季节性迁徙、鸟类逐渐改变纬度，还是人类活动的直接影响导致了这种变化，研究人员检查了1.5万只非候鸟的记录，它们生活在巴西西北部一片未被破坏的雨林中。
“We see these pretty remarkable changes in their bodies that are consistent with what we would expect under climate change,” says Vitek Jirinec at the Integral Ecology Research Center in California, who led the study.
“我们在它们的身体上看到了这些非常显著的变化，这与我们在气候变化下的预期一致，”领导这项研究的加州整体生态研究中心的Jirinec说。
The mean temperature of the birds’ habitat today is 1°C warmer in the wet season and 1.65°C warmer in the dry season compared with 1966. Weather patterns are also more extreme, with 13 per cent more rain falling in the wet season and 15 per cent less in the dry season.
与1966年相比，今天鸟类栖息地的平均温度在雨季高1°C，在旱季高1.65°C。气候模式也更为极端，雨季降雨量增加13%，旱季降雨量减少15%。
The birds lost mass more sharply following extremely dry or wet seasons. This could be a short-term response to changes in their environment, such as a lack of rainfall causing a decline in the number of insects that the birds feed on. But wingspan was significantly larger in one third of the species and the wing-to-mass ratio significantly smaller in two thirds of them, suggesting that the mechanisms behind the change could be complex and genetic rather than temporary.
在极度干旱或潮湿的季节之后，鸟类的体重会急剧下降。这可能是对环境变化的短期反应，例如缺乏降雨导致鸟类赖以生存的昆虫数量减少。但三分之一的物种的翼展显著增大，三分之二的物种的翼重比显著减小，这表明这种变化背后的机制可能是复杂的、遗传的，而不是暂时的。
“Mass is a generally good index of body condition in birds,” says Jirinec. “If they are simply not getting enough to eat, you would expect them to lose weight. But why would they have more energy to grow their wings?”
“质量通常是鸟类身体状况的良好指标，”Jirinec说。“如果它们只是吃不饱，你会预料到它们体重减轻。但为什么它们会有更多的能量来长翅膀呢？”
Birds and mammals of the same species are generally larger at higher latitudes. The leading theory is that their smaller surface-area-to-volume ratio allows them to better conserve heat. The inverse would help smaller species in hot climates to cool and could explain why birds are getting smaller as the climate warms, says Jirinec.
同一物种的鸟类和哺乳动物通常在高纬度地区体型较大。主要的理论是，它们较小的表面积与体积比使它们能够更好地保存热量。Jirinec说，相反的结果将有助于炎热气候中的小型物种降温，并可以解释为什么随着气候变暖，鸟类变得越来越小。