科学美国人60秒 气候变化导致动物数量减少，尤其鸟类（在线收听）

Climate Change Is Shrinking Animals, Especially Bird-Brained Birds

气候变化导致动物数量减少，尤其鸟类

Shahla Farzan: This is Scientific American’s 60-Second Science. I’m Shahla Farzan.

Climate change is affecting animals in a lot of different ways. But scientists have noticed a common trend across a variety of species: they’re getting smaller. As in—physically smaller in size. But why, and what could this mean?

Shahla Farzan：这是《科学美国人》的60秒科学。我是沙赫拉·法赞。

气候变化正在以许多不同的方式影响动物。但是科学家们已经注意到了一个普遍的趋势：它们正在变小。就像在物理上更小。但是为什么，这意味着什么？

Scientists have observed this phenomenon in very different animal species from wild sheep to woodrats. But it’s especially well-documented in North American songbirds. 

In 2019, researchers at the University of Michigan published a dataset of more than 70,000 birds that died after hitting windows in Chicago. The data showed the body sizes for dozens of species had actually shrunk over the past 40 years.

科学家们在从野生绵羊到林鼠的不同动物物种中观察到了这种现象。但在北美鸣禽中，这种现象的记录尤其丰富。 

2019年，密歇根大学（University of Michigan）的研究人员发布了一份数据集，其中包括7万多只在芝加哥撞窗后死亡的鸟类。数据显示，几十个物种的体型在过去40年里实际上已经缩小。

But when Justin Baldwin, a graduate student at Washington University in St. Louis, took a closer look at the data … something stood out. [Justin W. Baldwin et al., Phenotypic responses to climate change are significantly dampened in big-brained birds]

Justin Baldwin: There clearly seem to be some species that were shrinking a lot and other species that were shrinking much less.

但是当圣路易斯华盛顿大学的研究生贾斯汀·鲍德温仔细查看这些数据时，有些东西显得格外突出。

贾斯汀·鲍德温：很明显，似乎有些物种正在大量减少，而另一些物种则减少了很多。

Farzan: The question was … why were some bird species shrinking faster than others?

Baldwin and his colleagues had a feeling that bird behavior might be playing a role. 

In birds, species with bigger brains tend to be smarter and can change their behavior based on their environment. That means that they might be able to buffer themselves from increasing temperatures, says Carlos Botero, an assistant professor of biology at Washington University and the study’s co-author.

法赞：问题是……为什么有些鸟类比其他鸟类萎缩得更快？

鲍德温和他的同事们有一种感觉，鸟类的行为可能起到了一定的作用。 

在鸟类中，大脑更大的物种往往更聪明，可以根据环境改变行为。华盛顿大学生物学助理教授、该研究的合著者卡洛斯·博特罗说，这意味着它们可能能够缓冲温度升高带来的影响。

Carlos Botero: By adjusting their behavior, by changing the places that they look for food, the times of the day in which they do that, the things that they eat, and the ways in which they access those food sources. All those are ways in which they could experience a little bit less of a negative selection from all this variety of changes that we're seeing through climate change.

卡洛斯·博特罗：通过调整他们的行为，通过改变他们寻找食物的地点，一天中的时间，他们吃的东西，以及他们获取食物来源的方式。所有这些都是他们可以从我们通过气候变化看到的各种变化中少经历一点负面选择的方式。

Farzan: A bigger-brained bird, for example, might adjust its behavior and stay in the shadows when it’s hot.  

So the team decided to reanalyze that massive, original dataset—but this time, factor in brain size. 

They found birds with larger brains in relation to their body size are shrinking at slower rates than birds with smaller brains.

法赞：例如，一只大脑袋的鸟可能会调整自己的行为，在炎热的时候呆在阴影中。  

因此，研究小组决定重新分析这个庞大的原始数据集，但这一次，要考虑大脑的大小。 

他们发现大脑相对体型较大的鸟类比大脑较小的鸟类收缩速度较慢。

And that was true even after controlling for other factors that could affect how quickly these birds are evolving, like generation time and mutation rate. 

But Botero says, just because these larger-brained bird species can temporarily buffer themselves from warmer temperatures … it doesn’t mean they’re completely protected from climate change. 

即使控制了其他可能影响这些鸟类进化速度的因素，比如世代时间和突变率，这也是事实。 

但博特罗说，仅仅因为这些大脑较大的鸟类可以暂时缓冲自己免受更高温度的影响，并不意味着它们完全免受气候变化的影响。

Botero: It is important to realize that what we see here is not an indication that big brain birds are fine, and that they are not having any problems or that they are just capable to take whatever kind of change is coming from this suite of different environmental phenomena that is happening right now.

博特罗：重要的是要认识到，我们在这里看到的并不是大脑袋鸟类很好的迹象，也不是它们没有任何问题，或者它们只是有能力接受目前正在发生的一系列不同环境现象所带来的任何变化。

Farzan: Still, the team says there’s still a lot to learn when it comes to the ways in which bird behavior could affect how these species respond to climate change.

For one thing, in this study, there was only about a twofold difference in relative brain size between the species with the largest brain—the song sparrow—and the one with the smallest—the Swainson’s Thrush. 

法赞：尽管如此，该团队表示，在鸟类行为如何影响这些物种对气候变化的反应方面，仍有很多需要学习的地方。

首先，在这项研究中，大脑最大的物种——歌麻雀和大脑最小的物种——斯旺森画眉之间的相对大脑大小只有大约两倍的差异。

That means the responses could be even stronger in birds with larger brains, like crows, Baldwin says.

鲍德温说，这意味着大脑更大的鸟类，如乌鸦，其反应可能更强烈。

Baldwin: We're sampling only a small amount of the potential variation in relative brain size here in our study. And so that does suggest that even potentially small differences in relative brain size might actually have a large effect on ecological responses to climate change. 

鲍德温：在我们的研究中，我们只对大脑相对大小的一小部分潜在变化进行了取样。因此，这确实表明，即使相对大脑大小的微小差异实际上也可能对气候变化的生态反应产生重大影响。

Farzan: For now, Baldwin says, one of their biggest takeaways is that smaller-brained bird species could be particularly vulnerable as the climate continues to change. 

For Scientific American’s 60-Second Science, I’m Shahla Farzan. 

法赞：鲍德温说，就目前而言，他们最大的收获之一是，随着气候持续变化，大脑较小的鸟类物种可能特别脆弱。 

《科学美国人》的《60秒科学》，我是沙赫拉·法赞。