Even good fences make bad neighbours

好围栏也会造就坏邻居

Earth’s longest artificial structure is usually said to be the Great Wall of China. Just how long that is is hard to say, for northern China actually has many walls, built at different times and not always interconnecting. Earth’s second-longest artificial structure, though, is not a wall, but a fence. Its length is known exactly.It stretches for 5,614 km across eastern Australia and is intended to stop the country’s native feral dogs, the dingoes, which live mainly to its north, from preying on sheep, which are farmed mainly to its south.

世界上最长的人造建筑据说是中国的长城，但是它究竟有多长很难说，因为中国的北方实际上有很多城墙，修筑于不同的年代，而且有时彼此间并不相连。但世界上的第二长的人工建筑的长度是明确的，它不是城墙，而是一个围栏。长度绵延5614千米，横穿澳大利亚东部。建造它的目的是为了阻挡生活在北方的土狗捕食南方畜养的羊群。

Australia’s dingo fence is remarkable. But it does not stand alone. Millions of kilometres of fences wrap the world, outstripping the collective length of its roads by something like a factor of ten. Some are intended to curb the movement of animals, some the movement of people, and some merely to mark the limits of territory, so that everyone knows who owns what.

澳洲的野犬围栏很壮观，但是它并不是独一无二的。数百万千米的围栏包围了这个世界，超过了公路长度的10倍。有些是为了阻挡动物的移动，有些是为了阻止人的移动，有些仅仅是为了标记领土边界，这样大家就能指导谁拥有哪些土地。

Even fences built for other purposes, though, often serve to constrain animals, too. For example, some ecologists worry that the barrier now being erected along the border between America and Mexico, to stop the movement of human migrants, will also disrupt movement of endangered large mammals such as the Sonoran pronghorn and the desert bighorn sheep.

大多数的围栏还是为了限制动物的移动。比如有些生态学家担心现在正在建造的位于美国和墨西哥边境的围墙，虽说是为了阻止非法移民，但是也会扰乱一些濒危的大型野生动物的移动，比如北美叉角羚羊沙漠大角羊

Such worries are not foolish.Hardening borders in Central Asia,coupled with the expansion of fenced railways, have reduced numbers of another large,endangered mammal, the saiga antelope. Highway fencing in Sweden, erected to separate elks from speeding Volvos, limits those animals’ ability to range freely, and thus to find enough food. The region around the Maasai Mara game reserve, in Kenya—one of the world’s most famous—has also suffered. Growth in the amount of local livestock has led to the erection of fences that restrict the migration of wildebeest, zebras and Thomson’s gazelles,threatening a severe decline in their population.

这种担心并不是愚蠢的。中美洲坚硬的护栏，和一些不断增长的带护栏的告诉公路，已经减少了一些大型野生濒危哺乳动物的数量，比如赛加羚羊。瑞典的高速公路，为了防止驯鹿和高速行驶的汽车相撞，也减少了动物们自由活动，因此难以找到足够的食物。在 肯亚Maasai 地区的Mara保护区，世界上最有名的保护区之一，也遭受损失。当地不断增长的牲畜的数量带来了不断树立起的护栏，限制了牛羚，斑马和汤姆逊瞪羚的活动，造成了他们数量的极具减少

Disputed boundaries

有争议的边界

Until recently, data like these on the effects of fences on wildlife have been piecemeal. That has changed with the publication, in Bioscience, of a report compiled by Alex McInturff of the shengbaUniversity of California, Santa Barbara. Dr McInturff and his colleagues have attempted a comprehensive review of the scientific literature about fences and their environmental impact. 

直到最近，这样关于护栏对野生动物的的影响的数据也是非常零散。直到最近，加州大学圣巴巴拉分校的McInturff博士在生物科学杂志上发表了一篇文章。他和他的同事一起将关于围栏及其影响的文章做了一个非常全面的文献综述。

One discovery they have made is that more than half of published fence research focuses on just five countries—America, Australia, Botswana, China and South Africa—with America alone making up over a fifth. A second is that only a third of these studies examined the impact of fences on anything other than the target species involved, meaning the animals explicitly intended to be kept in or out.

其中一个发现就是有超过一半的文献集中在美国，澳大利亚，博茨瓦纳，中国和南非这五个国家，美国就占了超过五分之一。第二个发现就是只有三分之一的研究分析了围栏对于其他非特定目标动物的影响，意味着其他的动物被明确的排除或者列入在研究里。

Non-target species, however, are often those that have their fortunes most drastically reshaped by the appearance of poles and wire. Australian fences intended to keep out dingoes and other pests are also barriers to long-necked turtles, which travel great distances over land when moving between nesting sites. In Botswana veterinary fences erected to spare cattle from wildlife-borne disease result, as in the case of the Mara, in serious interference with wildebeest migrations. Fencing intended to protect the Qinghai-Tibet railway, in China, has similarly affected the migration routes of Tibetan antelope. Pangolins  curl up into a ball when endangered, in order to protect their soft underbellies. This is generally a wise move, but not when it causes them to embrace the wire of an electrifiedfence. Pronghorn tend to crawl under fences rather than jump over them (see picture), leading to hair loss that can increase the risk of hypothermia. And so on.

然而， 非目标的动物种类的命运，也因为这些杆子和铁丝网的出现而发生了巨大的改变。澳大利亚围栏本来是为了防止野犬和其他的害虫，但是也阻止了长颈乌龟的迁徙，他们要越过很长的距离在陆地和巢穴间来回。在博茨瓦纳的兽医围栏是为了保护牲畜免遭野生动物身上寄生的细菌，然后就如在肯亚Mara保护区里那样，牛羚的迁徙被影响。在中国，为了保护青藏铁路的围栏，也相同的影响了藏羚羊的迁徙。穿山甲会蜷缩成一个球体，当它遇到危险的时候，为了保护他们柔软的下腹部。这是一个明智的举动，但是当它们遇见的是带电的防护栏的时候就不是了。叉角羚喜欢爬过护栏下而不是跳过去。导致毛发的脱落，体温过低。

Not every creature fares badly. Hawks in Montana gladly perch on newly erected livestock fencing to prey on small herbivores, while fence-dwelling spiders in South Africa outperform their tree-based cousins when it comes to catching insects. Often, though, the winners are creatures that cause trouble for existing ecosystems. Excluding dingoes from large parts of Australia has allowed invasive red foxes to multiply, free from attack by what is, since the extinction of the thylacine, the country’s top predator. Native rodents have suffered as a result. Some have been brought to the brink of extinction. And fences erected around Tawharanui, a reserve  in New Zealand, have successfully excluded many undesirable large mammals that threaten the indigenous birdlife, but also keep out predators of house mice, an egg-eating alien whose numbers continued to rise.

并不是所有动物都过的不好。蒙塔纳州的老鹰就十分开心的栖息在牲畜护栏上捕食这些食草动物。在围栏上寄生的南非蜘蛛就比他们在树上寄生的表亲捕获了更多的昆虫。然而通常情况下，赢家都是能够对现有的生态系统造成麻烦的生物。围栏挡住了澳大利亚常见的野犬，却导致了侵略性很强的红狐狸的倍数增长，本来他们的天敌袋狼就已经灭绝。新西兰Tawharanui保护区的围栏已经成功的杜绝了很多威胁原著鸟类的大型野生动物，但是也挡住了家鼠的捕食者，他们偷吃鸡蛋为生，现在数量持续增长。

No sitting on the fence, please

请不要坐在围栏上

Smarter fencing can help. In the American West, for example, Montana and Wyoming are mounting campaigns to replace decades-old fences with ones that are more ecologically friendly. The changes required are often small. Making fences low enough for deer to jump over helps. So does raising the bottom wire sufficiently to allow pronghorn to crawl underneath. Adding horizontal poles improves a fence’s visibility, stopping unfortunate collisions at speed. And not all wire need be barbed.

智能围栏能够有所改善。在美国西部，蒙塔纳和怀俄明正在增加抗议活动，用一些对环境友好的围栏更加来替换一些几十年历史的旧围栏。这种改变通常成本不高，把围栏做的低一些，让鹿群可以跳过去。或者提高围栏基地让穿山甲可以爬过去。用一些横杆子来提高一个护栏的可见度，防止不幸的告诉冲撞。不是所有的铁丝网都需要带刺。

There is, though, also a need to paint a clearer picture of where fences are, and to remove those past their prime. Such flimsy structures are seldom well-documented and are difficult to pick out in satellite photographs, so doing this can be hard. Jeffrey Masek, a specialist in Earth-imaging at NASA, America’s space agency, suggests instead using commercial drones, which fly at low enough altitudes to capture detailed pictures. Derelict fences are of use to neither man nor beast. To beasts, in fact, they are positively anathema.

然而，这也需要去清楚的描绘出这些造成生态问题的围栏在哪里，然后替换那些已经陈旧的围栏。这些简陋的设施很少被记录完整，而且很难用卫星图给找出来，所以很难做到。Jeffrey Masek，一个NASA拍摄地球的专家说，与其用商用无人机，他们非常的高度很低，而且能够捕捉一个细节。破旧的围栏对人和动物都没有用，对动物来说，他们非常可憎。