Dragging a sleigh¹ laden² with enough presents for the world's children - not to mention a famously portly white-bearded gentleman - can be no easy feat³.

满载着全世界儿童的礼物的雪橇拖起来可不轻松，更别提上面还载着一位大名鼎鼎的白胡子胖先生。

But, since time immemorial, this crucial Christmas Eve duty has been performed with distinction by a team of beloved reindeer⁴.

但是，自古以来，一群可爱的驯鹿都能出色完成这个圣诞夜的重任。

Soon, however, Santa Claus may have to start looking around for a stronger type of animal, as new research reveals the species is becoming increasingly puny⁵.

不过，圣诞老人可能很快就得开始寻找更加强壮的动物了。因为新的研究显示，驯鹿正变得越来越瘦小。

A 16-year survey on the arctic Norwegian island of Svalbard found the reindeer there have declined in weight by an alarming 12 percent.

一项对挪威北极区域斯瓦尔巴特群岛长达16年的调查发现，这里的驯鹿体重下降了12%，这一数字让人震惊。

The reduction in average body-mass is being blamed on global warming.

全球变暖是驯鹿平均体重减轻的罪魁祸首。

In research presented lately at a meeting of the British Ecological⁶ Society in Liverpool, scientists will explain how rising temperatures are depriving female reindeer of nutrients⁷ during important phases of gestation⁸.

日前，科学家们在利物浦英国生态学会的会议上展示了这项研究成果，他们将解释在雌性驯鹿怀孕的关键阶段，气温升高是如何令其失去营养的。

Snow in Svalbard typically covers the ground for eight months of the year, which, combined with low temperatures, limits grass growth to June and July.

通常，斯瓦尔巴德岛一年中有八个月都被白雪覆盖，而且气温极低，小草的生长期仅限于六月和七月。

But as summer temperatures have increased by around 1.5℃, pastures have become more productive, allowing female reindeer to gain more weight by the autumn and therefore to conceive more calves⁹.

但由于夏季气温升高了约1.5℃，牧草地变得更茂盛，这使得雌性驯鹿到了秋天会变胖且能孕育更多小鹿。

However, warmer winters have brought with them greater rainfall which freezes when it settles on the snow, thereby¹⁰ locking out the reindeer from the life-sustaining food below.

然而，温暖的冬天带来了更多的降雨，雨水落在雪地里会结冰，阻止驯鹿获得冰面下维持生命的食物。

As a result, female reindeer are becoming starved, causing them to abort¹¹ their calves or giving birth to much lighter¹² young.

结果，饥饿的雌性驯鹿就会流产或者诞下体重较轻的小鹿。

The average mass of an adult reindeer in 1994, when the survey began, was 55kg, but by 2010 it had dropped to 48kg.

1994年调查开始时，一头成年驯鹿的平均体重为55公斤，但是到2010年，成年驯鹿的平均体重已经下降到48公斤。

Professor Steve Albon, an ecologist at the James Hatton Institute in Aberdeen, said that, because the mammals have a relatively¹³ high surface-area-to-volume ratio, they are no particularly energy efficient.

史蒂夫.阿尔博教授是阿伯丁詹姆士赫顿研究院的生态学家。他表示，这种哺乳动物的表面积体积比相对较高，他们没有特殊的节能功能。

Reindeer can often access the meagre food sources beneath the snow by clearing it away with their antlers, but they cannot break through the hard ice.

驯鹿通常用鹿角清除积雪，获得下面寥寥无几的食物，但他们无法弄破坚冰。

Without access to the food in winter, calves are being born far lighter than they should be.

雌性驯鹿冬天吃不到食物，生下来的小鹿就比应有的体重轻得多。

Numbers of reindeer have also soared in the past 20 years, meaning that those which are born are facing greater competition for food.

驯鹿的数量在过去的20年里飙升，这意味着生下来的小鹿面临着更加激烈的食物竞争。

"The implications are that there may well be more smaller reindeer in the Arctic in the coming decades, but possibly at risk of catastrophic die-offs because of increased ice on the ground," said Professor Albon.

阿尔博教授称，“这背后的含义是，虽然未来几十年里很可能出现更多瘦小的驯鹿，但地上的冰面越来越大，它们因此存在灭绝的风险。”

Despite the gloomy findings, reindeer appear to be suffering less from the impact of climate change than some other arctic species.

尽管这一研究发现很悲观，但是驯鹿受气候变化的影响似乎比其他北极生物要小。

Last week the scientists warned that a third of the world's polar bears could disappear in the next 40 years to melting Arctic sea ice.

科学家们上周警告称，随着北冰洋冰面的消融，全球三分之一的北极熊可能在未来40年内消失。