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Grazing Cattle Trim the Menu for Birds

愿为鸟儿修改食谱的牛群

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?

当鸟类栖息地遭遇破坏时，其中一些物种会因此灭绝，而有些物种则会生存下来。但在整个过程开始时，即鸟类的栖息地开始发生变化时发生了什么呢?

Research in Argentina's Monte Desert has provided some answers. Protects parts of the desert have lots of plant diversity: trees, tall shrubs¹, 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 nutrients² they need with minimal³ effort.

阿根廷蒙特沙漠所做的科学研究为我们提供了一些答案。在受保护的部分沙漠地区，其植物多样性较丰富：树木、高灌木、矮灌木、草地以及开花植物应有尽有。在有如此多选择的情况下，大多数以种子为食的鸟类会选择吃较大的草籽。这样只需付出一点努力，这些鸟就能获得它们所需的所有能量和营养。

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 jeopardy⁴。

但是当这片沙漠植被区出现放牧的牛群时，这里的鸟类就面临着食物供应发生变化的问题。这时，有一些鸟类会很乐意改变它们的饮食习惯。而另一些则不然。正是那些不肯改变生存方式的鸟类面临的风险最大。了解鸟类对放牧群体出现的反应，可以帮助自然资源保护主义者找出帮助那些最危险物种的办法。

Ecologists from the Argentine Arid⁵ Zones Research Institute compared soil samples from the desert's ?acu?án biosphere⁶ reserve to samples from two neighboring cattle ranches⁷. They discovered that grass seeds—the birds' favorites—were just one quarter as likely to be found in the ranches compared with the reserve.

来自阿根廷干旱地区研究所的生态学家们将沙漠中Nacunan生物圈保护区的土壤样本与两个相邻的牛牧场的土壤样本进行了比较。他们发现，牛牧场内发现的鸟类最爱的草籽似乎仅是保护区内发现的四分之一。

Next, they captured birds and flushed their digestive tracts⁸ to see what they were eating. The Common Diuca-Finch⁹ [finch sounds] and the Rufous-Collared Sparrow [sparrow sounds] had adjusted their diets, opting¹⁰ to dine on their less preferred options at the ranches, even while they still focused on large grass seeds in the reserve.

然后，他们捕捉鸟类并对它们的消化道进行冲洗以观察其进食情况。普通的拉丁雀和红领带鹀调整了它们的饮食习惯。它们选择在牧场上吃它们并不太喜欢的食物，虽然在保护区内它们仍然会主要去进食较大的草籽。

Meanwhile, the Many-Colored Chaco Finch [chaco finch sounds] and the Ringed Warbling-Finch [warbling finch sounds] were apparently¹¹ unable to switch their foraging¹² 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 rigidity¹³ could limit their ability to reproduce or to care for their young. The results are in the journal The Condor¹⁴.

与此同时，彩雀和黑领歌鹀明显无法改变它们的觅食策略。即使是在牧场，它们也仍会努力寻找数量较少的可食用的大草籽。如果它们为此消耗的能量大于它们能找到的食物的能量，那它们就会挨饿。即便作最乐观的估计，这种饮食结构僵化也会限制它们的繁殖能力或照顾其后代的能力。该研究结果发表在《秃鹫》杂志上。

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 livestock¹⁵ to graze. For example, the ranchers can plant species for their cattle that will also be more palatable¹⁶ and nutritious¹⁷ for local seed-eating birds. The cows won't care about the menu change—but the birds sure will.

这样的研究有助于预测在退化的栖息地中，哪些物种面临的风险更高，还可以帮助牧场主在放牧的同时保护这些脆弱的物种。比如，牧场主可以为牛群种植那些同时能够为当地食草籽的鸟类提供更有营养价值也更美味的植物。虽然牛群不会在意它们食谱的变化——但那些鸟类却会。