Seabirds racing home over the ocean can get jet-lagged

本文为原文前 6,000 字符的节选翻译，完整内容请查看原文。

Flying across several time zones often causes jet lag, a feeling when the body insists it’s the middle of the night while the clock says it’s lunchtime. Now it turns out this nuisance is not exclusive to humans. A new Science study on Manx shearwaters, seabirds that can fly hundreds of kilometers a day over the North Atlantic, shows they jet-lag themselves during their excursions. And because these birds navigate by the Sun, that jet lag leaves a measurable mark—it skews their compass.

跨越多个时区飞行通常会导致时差反应，即身体感觉正处于深夜，而时钟却显示是午餐时间。现在看来，这种困扰并非人类所独有。一项关于马恩岛水薙鸟（Manx shearwaters）的最新《科学》研究表明，这些每天能在北大西洋上空飞行数百公里的海鸟在迁徙过程中也会产生时差。由于这些鸟类依靠太阳导航，这种时差会留下可测量的痕迹——它会使它们的指南针发生偏转。

Patrick Lewin is a behavioral and sensory ecologist at the University of Oxford and lead author of the study. “Manx shearwaters are medium-sized birds, about the same size as a pigeon,” Lewin said. “They are white underneath and black on top, but they have very long wings, and they are closely related to albatross.” Manx shearwaters nest in burrows on coastal islands around the North Atlantic. Most breed around the UK and Ireland, with about half of their population living in Wales.

帕特里克·卢因（Patrick Lewin）是牛津大学的行为与感官生态学家，也是该研究的主要作者。“马恩岛水薙鸟是中等体型的鸟类，大约和鸽子一样大，”卢因说。“它们腹部呈白色，背部呈黑色，但翅膀非常长，与信天翁亲缘关系密切。”马恩岛水薙鸟在北大西洋沿岸岛屿的洞穴中筑巢。大多数在英国和爱尔兰周边繁殖，其中约一半的种群生活在威尔士。

From there, they head out to feed anywhere from a few dozen to more than 1,000 kilometers into the Atlantic. To get back, shearwaters are thought to work out where they are located using a map sense, possibly based on smells, and then use the Sun as a compass to set their direction. The trouble with navigating by the Sun, though, is that it moves across the sky. “You can imagine an animal or a human that wants to travel south all day. At sunrise, when the Sun’s in the east, it needs to be traveling 90 degrees clockwise of the Sun, but by midday it needs to be traveling straight towards the Sun, and by sunset it needs to be traveling 90 degrees anticlockwise of the Sun,” Lewin said.

从那里出发，它们会前往大西洋深处觅食，距离从几十公里到一千多公里不等。人们认为，水薙鸟在返回时会利用一种地图感（可能基于气味）来确定自己的位置，然后利用太阳作为指南针来设定方向。然而，依靠太阳导航的问题在于太阳会在天空中移动。“你可以想象一只动物或一个人想要整天向南旅行。在日出时，当太阳在东方，它需要向太阳顺时针90度的方向飞行；但到了中午，它需要直接朝着太阳飞行；而到了日落时，它需要向太阳逆时针90度的方向飞行，”卢因说。

Effective navigation by the Sun requires a clock that tells you what time of day it is. Birds, like nearly all animals, have such a clock built in. But the clock in Manx shearwaters is not perfect. The birds recalibrate their internal clock at every dusk and dawn. This means that for every degree of longitude a bird covers between sunrise and sunset, its clock falls four minutes out of sync with local time. In consequence, a Manx shearwater misjudges where the Sun should be and veers off course clockwise when it flies east, or anticlockwise when it flies west.

有效的太阳导航需要一个能告知当前时间的时钟。像几乎所有动物一样，鸟类体内也内置了这样的时钟。但马恩岛水薙鸟体内的时钟并不完美。这些鸟类在每个黄昏和黎明都会重新校准它们的生物钟。这意味着鸟类在日出和日落之间每飞行一度经度，其生物钟就会与当地时间产生四分钟的偏差。因此，马恩岛水薙鸟会误判太阳的位置，在向东飞行时向顺时针方向偏离航线，或在向西飞行时向逆时针方向偏离。

Scientists had already shown something similar in other birds by catching penguins and quickly moving them across lines of longitude, but before Lewin’s study no one had clearly demonstrated it in wild animals moving on their own, mostly because the effect is small, and so requires a lot of data to become apparent. But Lewin’s team happened to have just the right database.

科学家们此前曾通过捕捉企鹅并将其快速跨经度移动，在其他鸟类身上展示过类似的现象，但在卢因的研究之前，没有人能在野生动物自主移动的情况下清晰地证明这一点，主要是因为这种影响很小，需要大量数据才能显现出来。但卢因的团队恰好拥有合适的数据集。

Tim Guilford, Lewin’s supervisor at Oxford, and Chris Perrins, a long-time Oxford shearwater researcher, started fitting shearwaters with GPS tags in 2004, when the devices first became small enough for a bird this size. Two decades later, the team had tracks from 3,688 foraging trips made by 1,045 birds from colonies along the UK’s western coasts. Those trips last from one day up to two weeks. From this dataset, Lewin and his colleagues separated homeward flights, which the scientists say was rather simple.

卢因在牛津大学的导师蒂姆·吉尔福德（Tim Guilford）和长期研究水薙鸟的牛津研究员克里斯·佩林斯（Chris Perrins），在2004年设备首次小型化到足以安装在如此体型的鸟类身上时，就开始为水薙鸟安装GPS标签。二十年后，该团队获得了来自英国西海岸栖息地的1,045只鸟类进行的3,688次觅食航迹。这些行程持续时间从一天到两周不等。从这个数据集中，卢因和他的同事们分离出了返巢飞行，科学家们称这一过程相当简单。

Foraging shearwaters make short, wiggly flights between dives. “When they are deciding to go back to their colony, they kind of switch into this mode where they are flying as fast as they can in pretty much a straight line continuously without stopping for really long periods,” Lewin said. For each homing flight, the researchers worked out where the bird last saw the sunrise, at which point its clock should have matched local time. Then, at every GPS fix, they calculated how far east or west it had traveled since, and how much that would bend its Sun compass.

觅食的水薙鸟在潜水间隙会进行短促且蜿蜒的飞行。“当它们决定返回栖息地时，它们会切换到一种模式，即以最快速度持续飞行，几乎呈直线，且长时间不停歇，”卢因说。对于每一次返巢飞行，研究人员都会计算出鸟类最后一次看到日出的地点，此时其生物钟应与当地时间一致。然后，在每一个GPS定位点，他们计算出该鸟自那时起向东或向西飞行了多远，以及这会对其太阳指南针产生多大的偏差。

Since they knew each bird was headed exactly to its burrow, they could compare those predictions with how the birds actually deviated from their course. The time shifts were tiny. “About an hour is pretty much the maximum that we observed. Most of these are probably 15-minute, 10-minute time differences,” Lewin says. “For us, that would be pretty imperceptible, but it does still have an effect on their compass orientation that we can detect.”

由于他们知道每只鸟的目标都是自己的洞穴，他们可以将这些预测与鸟类实际偏离航线的情况进行比较。时间偏差非常微小。“我们观察到的最大偏差大约是一个小时。大多数偏差可能只有15分钟或10分钟，”卢因说。“对我们来说，这几乎是察觉不到的，但它确实对它们的指南针定向产生了我们能够检测到的影响。”

Across 335 homing flights made out of sight of land, the birds veered just as the Sun compass predictions said they would. Because the study was not a controlled experiment, though, Lewin argues we need to be careful about causality. Still, the team calculated the biases that crosswinds, the Coriolis effect, or a magnetic compass might introduce, and none of those fit the data well. “Our observed biases match by far the best to the Sun compass biases that we would expect,” Lewin said.

在335次远离陆地的返巢飞行中，鸟类的偏离方向正如太阳指南针预测的那样。不过，由于这项研究并非受控实验，卢因认为我们需要谨慎对待因果关系。尽管如此，团队还是计算了侧风、科里奥利效应或磁罗盘可能引入的偏差，但这些因素都无法很好地拟合数据。“我们观察到的偏差与我们预期的太阳指南针偏差最为吻合，”卢因说。

The navigational errors apparently caused by jet lag reached up to around 15 degrees, which for birds was way less costly than one might expect. A bird with a map sense can check its position, notice it’s drifting, and correct. The team calculated that for a shearwater flying 1,000 kilometers east in a day, about the maximum the scientists observed, the average error would be roughly seven degrees. If the bird keeps checking where it is, that adds only five kilometers to the trip.

由时差引起的导航误差最高可达15度左右，这对鸟类来说代价远比人们预想的要小。拥有地图感的鸟类可以检查自己的位置，注意到偏离并进行修正。团队计算得出，对于一只一天向东飞行1,000公里的水薙鸟（这是科学家观察到的最大距离），平均误差约为7度。如果鸟类不断检查自己的位置，这只会给行程增加5公里的路程。

The researchers also found that when shearwaters followed coastlines, they still drifted slightly closer to or farther from the shore depending on their expected compass error. Work done in Oxford two decades ago showed that homing pigeons with shifted clocks do the same, even while following a familiar road. This led researchers to hypothesize that birds may run two parallel navigation systems, one based on the compass and one on familiar landmarks, with the balance between them never tipping entirely to one side. An alternative explanation, Lewin suggests, might be that they don’t know exactly where on the coast they are and use the Sun to pick which way to follow it. “We don’t

研究人员还发现，当水薙鸟沿着海岸线飞行时，它们仍会根据预期的指南针误差稍微靠近或远离海岸。二十年前在牛津进行的研究表明，生物钟被调整过的信鸽在沿着熟悉的道路飞行时也会出现同样的情况。这促使研究人员推测，鸟类可能运行着两套平行的导航系统，一套基于指南针，另一套基于熟悉的地理标志，两者之间的平衡从未完全偏向任何一方。卢因提出，另一种解释可能是它们并不确切知道自己在海岸的什么位置，因此利用太阳来选择沿海岸线的飞行方向。“我们不……”