A male bay-breasted warbler, one of the species of smaller-brained birds, researchers said were more affected by climate change.

一只雄性栗胸林莺，研究人员说，这是一种脑部较小的鸟类，更易受气候变化的影响。

(CNN)Thousands of birds die each spring and fall when they collide with Chicago's skyscrapers, which lie on a major migration path between Canada and Latin America.

（美国有线电视新闻网，Cable News Network，简称CNN）每年春季和秋季，成千上万的鸟类撞上芝加哥摩天大楼而死，这些摩天大楼位于加拿大和拉丁美洲之间的一条主要迁徙路线上。

But the birds don't die in vain. Since the 1970s, many of them have been collected from the street and cataloged by the city's Field Museum. This unique and detailed set of data has been a scientific windfall, revealing that North American migratory birds appear to be shrinking in response to climate change.

但是鸟儿们并不会白白死去。自20世纪70年代以来，许多街上的鸟儿都会被收集起来，并被该市的菲尔德博物馆（Field Museum，一般指菲尔德自然史博物馆，全称Field Museum of Natural History）登记分类。这给科学(研究) 带了一份意外的，却又独特而详细的数据，揭示了北美候鸟似乎正在因气候变化而缩小。

A new study of this data has highlighted an important nuance in this trend: Birds that have bigger brains, relative to their body size, are not shrinking as much as their smaller-brained counterparts.

这份数据的一份新研究强调了这一趋势中的一个重要细微差别：相对于身体尺寸而言大脑更大的鸟类，他们的身体并不像大脑较小的鸟类那样缩小。

The study is the first to identify a potential lix between cognition and animal response to human-made climate change, according to the researchers from Washington University in St. Louis.

圣路易斯华盛顿大学的研究人员称，这项研究首次发现了认知结果与动物对人为气候变化的反应之间的潜在联系。

"As temperatures warm, body sizes are decreasing," said Justin Baldwin, a doctoral student at Washington University and author of the study that published this week in the journal Ecology Letters, in a news release. "But larger-brained species are declining less strongly than small-brained species."

该研究本周在《Ecology Letters》发表，华盛顿大学的一名博士生Justin Baldwin是这份研究的作者。他在一份新闻稿中说道，“随着气候变暖，鸟类的身体尺寸变小。但是与大脑较小的物种相比，大脑较大的物种减小的要少得多。“


Since the 1970s, migratory birds that died after colliding with Chicago buildings have been collected and cataloged by the Field Museum. The data set is showing how birds are affected by climate change.

从19世纪70年代开始，撞击芝加哥大楼而死的候鸟被菲尔德博物馆收集并登记分类。这个数据集显示了鸟类是如何受气候影响的。

Relative brain size is often considered an indicator of behavioral flexibility in birds, according to the research. The idea is controversial when it's applied to some other animals, Baldwin said, but it works for birds.

研究表明，大脑的相对大小通常被视作是鸟类行为灵活性的一个指标。Baldwin表示，这个想法应用在其他动物身上时虽然是存在争议的，但是对于鸟类来说是适用的。

"Relative brain size correlates with increased learning ability, increased memory, longer lifespans and more stable population dynamics," Baldwin said.

Baldwin 说，“大脑的相对大小与学习能力的提高、记忆力的增强、寿命的延长以及更稳定的人口动态是相关的。“

"In this case, a bigger-brained species of bird might be able to reduce its exposure to warming temperatures by seeking out microhabitats with cooler temperatures, for example," he said.

“例如，在这个情况下，一种大脑较大的鸟类可能能够通过寻找温度较低的微栖息地来在减少在变暖的温度下的暴露。“他表示。

The researchers analyzed information from 70,000 birds that died when they collided with buildings in Chicago between 1978 and 2016. They added brain volume measurements and life-span data for 49 of the 52 species in the database.

研究者分析了来自1978年到2016年70000只撞击芝加哥大楼而死的鸟类的信息。他们在数据库中添加了52种物种中49种的脑容量测量数据和寿命数据。

Birds that had big brains, relative to their bodies such as the song sparrow and other New World sparrows, had body-size reductions that were only about one-third of those observed for birds with smaller brains, the study found. Wood warblers (Parulidae) tended to have smaller brains and tended to shrink more.

研究发现，相对于身体而言，大脑较大的鸟类(如北美歌雀和其他新大陆麻雀)身体尺寸的缩小幅度仅为大脑较小鸟类的三分之一左右。林莺（林莺科）的大脑往往较小，而且其身体尺寸往往缩小得更多。

"The authors from that amazing study shared their raw data ... which allowed us to add to it and discover more," Baldwin said via email.

Baldwin 通过邮件表示，“这项研究令人称奇，它的作者分享了他们的原始数据，这让我们能够添加这份数据并认识到更多。“


A Blackburnian warbler, pictured here, was another of the species of smaller-brained birds that were more strongly affected by climate change.

图中所示的一只啭鸟是另一种受气候变化影响更大的大脑较小的鸟类。

Shape-shifters

形态变化

It's not known exactly why birds are shrinking in size. Larger body size helps animals in cold places stay warm, while a smaller body retains less heat.

目前尚不清楚鸟类体型缩小的确切原因。较大的体型有助于寒冷地区的动物保持温暖，而较小的体型保留的热量较少。

Bird wingspans may have increased to compensate for smaller bodies that produce less energy for the incredibly long distances traveled during migration, researchers have also found.

研究人员还发现，在路途遥远的迁徙过程中，较小的身体产生的能量较少，鸟类翼展的增加可能是为了弥补这一点。
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Similarly, other research has found that some animals are developing larger beaks, legs and ears that allow them to better regulate body temperature as the planet gets hotter. While most of the morphological changes have been in birds, bats and shrews have also been affected. Climate change has even altered human bodies.

类似地，其他研究发现，一些动物正在发育更大的喙、腿和耳朵，以便在地球变得更热时更好地调节体温。虽然大多数形态变化发生在鸟类身上，但蝙蝠和鼩鼱也受到了影响。气候变化甚至改变了人类的身体。
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However, downsizing comes at a potential cost for a bird, with an increased risk of falling prey to predators or making it harder to compete for resources with other bird species, said study coauthor Carlos Botero, assistant professor of biology at Washington University, in the statement.

然而，该研究的共同作者、华盛顿大学(Washington University)生物学助理教授Carlos Botero在声明中说，缩小体型对一只鸟来说是有潜在代价的，它成为捕食者猎物的风险增加，或使其更难与其他鸟类竞争资源。

It's in this context that having a larger brain may offer alternatives that are not available to small-brained species, he said.

他说，在这种情况下，拥有一个更大的大脑可能另有选择，而这些选择是小脑袋物种无法获得的。

"One of the first things that jumps out to me from these findings is that we can already see that climate change is having a disproportionate effect on species that have less capacity to deal with environmental change through their behavior," Botero said.

Botero说道，“从这些发现中我首先想到的一件事是，我们已经发现，气候变化对那些通过行为应对环境变化能力较弱的物种产生了太大的影响，“

"This doesn't mean that climate change is not affecting brainy birds ... or that brainy birds are going to do just fine. What our findings suggest is that climate change can have a much stronger effect on the less-brainy birds."

“这并不意味着气候变化不会影响十分聪明的鸟类…或者聪明的鸟类将能够很好的应对。我们的研究结果表明，气候变化会对不那么聪明的鸟类产生的影响要大得多。“

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