When cattle graze the desert's natural landscape, birds face changes in food availability—and some species are unable to adapt. Jason Goldman reports.

当家畜在沙漠自然景观区吃草时,鸟类则将面临食物供应的改变——其中一些物种将无法适应该变化。

撰文 Jason G. Goldman 贾森 G. 戈德曼

翻译 许楠

审校：郭晓

When birds face the destruction of their habitat, some species don’t make it while others survive. But what happens at the very beginning of the process, just as a bird's habitat starts to change?

当鸟类面临栖息地破坏时，一些物种将无法适应这一变化，而另外一些也许能幸存下来。但是在该过程刚刚开始的时候，即鸟类栖息地变化之初，发生了什么呢？

Research in Argentina's Monte Desert has provided some answers. Protects parts of the desert have lots of plant diversity: trees, tall shrubs, short shrubs, grasses and flowering plants. With so many options, most seed-eating birds choose to feast on large grass seeds. The birds can get all the energy and nutrients they need with minimal effort.

在阿根廷莫提大沙漠（Argentina’s Monte Desert）的研究为我们提供了一些答案。沙漠保护区有丰富的植被多样性：树木、高灌木丛、矮灌木丛、草类和开花植物。在这么多的选择中，大多数以种子为食的鸟类会选择食用大颗粒的草籽。如此一来它们就可以花费最少的努力而得到全部所需的能量和营养。

But when cattle show up to graze the desert's natural landscape, birds face changes in food availability. Some birds are happy to change their diets in response. Others, not so much. And it's the ones set in their ways that are at the highest risk. Understanding how birds react to grazing can help conservationists figure out how to help those species most in jeopardy

但是当家畜出现在沙漠自然景观区吃草的时候，鸟类就要面临食物供应的改变。一些鸟类很乐于改变其饮食结构，而另一些则并不十分乐意——这些固守成规的鸟类在生存上就将面临高风险。了解鸟类对放牧的反应可以帮助自然资源保护者找到办法，来保护这些大多处于险境的物种。

Ecologists from the Argentine Arid Zones Research Institute compared soil samples from the desert's Ñacuñán biosphere reserve to samples from two neighboring cattle ranches. They discovered that grass seeds—the birds' favorites—were just one quarter as likely to be found in the ranches compared with the reserve.

阿根廷干旱区研究机构的生态学家们对比了Ñacuñán沙漠生物圈保护区和附近的两个牧场的土壤样本。他们发现鸟类最喜欢食用的草籽在牧场中的量只有保护区的四分之一

Next, they captured birds and flushed their digestive tracts to see what they were eating. The Common Diuca-Finch [finch sounds] and the Rufous-Collared Sparrow [sparrow sounds] had adjusted their diets, opting to dine on their less preferred options at the ranches, even while they still focused on large grass seeds in the reserve.

接下来，他们捕获了一些鸟，并灌冲食道来看它们吃了什么。其中狄卡雀和红领带鹀已经调整了它们的饮食结构：在牧场，它们选择次优食物，即使它们在保护区的首选食物仍然是大草籽。

Meanwhile, the Many-Colored Chaco Finch [chaco finch sounds] and the Ringed Warbling-Finch [warbling finch sounds] were apparently unable to switch their foraging tactics. Even at the ranches, they worked hard to find the few grass seeds available. If they burn more energy foraging than they get from the few seeds they find, they could starve. At best, their dietary rigidity could limit their ability to reproduce or to care for their young. The results are in the journal The Condor. [Luis Marone et al, Diet switching of seed-eating birds wintering in grazed habitats of the central Monte Desert, Argentina]

同时，彩雀和黑领歌鹀则很明显不能够改变它们的饮食习惯。即使在牧场区，它们也会非常努力地寻找罕见的大草籽。如果他们在寻找草籽时消耗的能量比从草籽中获得的更多，那它们就要挨饿了。就最乐观的一面看，它们对饮食的恪守会限制它们的生育能力及对后代的抚养。这一结论被发表在《秃鹰》（The Condor）杂志中。[Luis Marone et al, Diet switching of seed-eating birds wintering in grazed habitats of the central Monte Desert, Argentina]

Studies like this can help predict which species are at higher risk in degraded habitats. And they can help ranchers protect these vulnerable species, even while allowing their livestock to graze. For example, the ranchers can plant species for their cattle that will also be more palatable and nutritious for local seed-eating birds. The cows won't care about the menu change—but the birds sure will.

此类研究可以帮助预测哪些物种在栖息地退化时会面临较高的风险，并帮助牧场主来保护这些物种，即使他们的家畜仍在此食用草料。例如：牧场主可以为家畜种植一些可以同时为当地食谷鸟类提供可口且有营养的植物。牛并不会介意它们食谱的改变——但是鸟类的确会介意。