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This is Scientific American — 60-Second Science. I'm Christopher Intagliata.

这里是科学美国人——60秒科学。我是克里斯托弗·因塔利亚塔。

Every winter, huge hordes¹ descend² upon the parking lots of big box stores. Not Black Friday shoppers... but crows. There's videos all over YouTube.

每年冬天，都会有一大群降临到大卖场的停车场。这里指的并不是黑色星期五的购物者，而是乌鸦。YouTube网站随处可见有关乌鸦的视频。

(YouTube clip: "And as you can see they're in the trees, they're on the rooftop over there, and it's like Hitchcock's The Birds...")

（YouTube网站视频片段：“如你所见，树上、那边的屋顶上全是乌鸦，就像是希区柯克的作品《群岛》中所描述的情景……”）

"So sometimes there are 4,000, 10,000, even 20,000 birds in these flocks."

“有时这些乌鸦群中的个体数量达到4000、10000甚至是20000只。”

Andrea Townsend is a behavioral ecologist at Hamilton College in New York.

纽约哈密尔顿大学的行为生态学家安德莉亚·汤森德说到。

"They're really noticeable because what they like are urban areas. So you'll see them in well-lit urban parking lots. That's sort of their favorite place to spend the winter."

“这些乌鸦群非常显眼，因为它们喜欢城区。因此，人们会在灯火通明的停车场看到它们。可以说那里是它们最喜欢的过冬地。”

Crows, she says, are what's known as "partial migrants." Every year, some members of the population migrate between breeding grounds and their overwintering grounds—like parking lots. But others just stay put. So Townsend and her colleagues wanted to know if that urge to migrate was something individual crows can turn on and off?

她说，乌鸦被认为是“部分候鸟”。每年，乌鸦群中会有一些成员往返于繁殖地和停车场等过冬地之间。但是其它乌鸦则会留在原地。因此，汤森德和同事想知道，乌鸦个体是否能开启并关闭这种迁徙的欲望。

To find out, they captured 18 crows from overwintering spots in California and New York. They fitted the birds with little backpack satellite tags, and tracked them for several years. Overall, three quarters of the birds migrated, an average of 300 miles. And more importantly, if they migrated once, they did it every year—suggesting traveling is not a habit they switch on and off.

为了找到答案，他们在加利福尼亚州和纽约州的过冬地点捕获了18只乌鸦。他们在这些乌鸦身上安装了小型背包式卫星标记，并对它们进行了数年的追踪。总的来说，有四分之三的乌鸦会迁徙，平均路程为300英里。更重要的是，如果它们迁徙过一次，那它们每年都会迁徙——这表明迁徙并不是它们可调控的习惯。

The researchers also found that migrating crows returned faithfully to the same breeding grounds every year—but were more flexible on where to overwinter. Which could be a good thing.

研究人员还发现，迁徙乌鸦每年会忠诚地回到同一个繁殖地，但在过冬地的选择上则更为灵活。这可能是件好事。

"Birds with these flexible strategies can change their behavior when the environment changes. Whereas other birds are more locked into their overwintering sites. And those birds may not be able to adjust so quickly or as easily to changing environmental conditions like climate change."

“策略灵活的乌鸦可以随环境变化而改变它们的行为。而其它乌鸦则会锁定过冬地。这些乌鸦也许无法如此迅速或容易地适应气候变化等环境条件的变化。”

The study is in the journal The Auk: Ornithological³ Advances.

这项研究发表在《海雀：鸟类学发展》期刊上。

Next, Townsend wants to investigate whether migration⁴ is a mental trade-off for the birds—since migrants have to keep all that location data in mind. "So maybe it's not as good at solving problems as a resident bird that doesn't have to invest so much in that long-term memory." Then again, with all that time on the wing—migrants simply may not have as much free time to puzzle over problems.

接下来，汤森德想研究迁徙对乌鸦来说是否是一种心理权衡——因为候鸟必须记住所有繁殖地和过冬地的位置数据。“也许乌鸦解决问题的能力不及留鸟，因为留鸟不必在长期记忆上投入如此之多。”另外，由于迁徙时总是在飞行，候鸟也许仅仅是没有那么多空闲时间去思考问题。

Thanks for listening for Scientific American — 60-Second Science. I'm Christopher Intagliata.

谢谢大家收听科学美国人——60秒科学。我是克里斯托弗·因塔利亚塔。