In just five hours, an average farm pig can learn how to interpret an image in the mirror and use it to find hidden food.

Scientists consider the ability to use a mirror a sign of complex cognitive processing and an indication of a certain level of awareness. In addition to humans and some primates, dolphins, elephants, magpies and a famous African grey parrot named Alex have all been known to retrieve objects or remove marks on their body using a mirror. Now it looks like pigs should be added to the list of clever critters that can master a mirror: After spending five hours with a mirror in their pen, seven out of eight pigs could use the reflection to find a hidden bowl of grub.

"This is the first demonstration of the ability of pigs to use mirrors," animal behavior expert Donald Broom of the University of Cambridge wrote in an e-mail. "Finding sophisticated learning and awareness in animals can alter the way that people think about the species and may result in better welfare in the long run." Broom co-authored the paper published this month in Animal Behaviour.

Like most animals, the pigs were immediately curious when researchers placed the shiny, reflective object in their pen. They approached the mirror until they bumped into it with their snout, and then checked to see what was behind the mirror. The pigs spent an average of 20 minutes gazing at their reflection, often turning in different directions to inspect themselves from several angles.

"These kind of movements suggest that the pigs were correlating the movements of their body with the visual stimulus they were receiving from the mirror, and so learning the contingency between the two," biologist Louise Barrett of the University of Liverpool wrote in a commentary about the paper, also published this month in Animal Behaviour.

After five hours with a mirror, the pigs were placed in a new test area that contained a food bowl hidden behind a barrier. Although the pigs could see the reflection of the bowl in the mirror, they couldn't see the food directly. A fan above the bowl circulated the scent of food around the room, prohibiting the pigs from smelling their way to the treat.

Seven out of eight of the pigs with previous mirror experience spotted the reflection of the food bowl and correctly interpreted its location: Instead of searching for the food in its apparent position behind the mirror, the pigs headed around the barrier and straight for the true location of the bowl. When the researchers tested pigs with no prior mirror exposure, however, nine out of 11 of them became confused, searching behind the mirror for the food.

"These results suggest not only that pigs learn the contingency between their own movements and their image in the mirror," Barrett wrote, "but that their knowledge incorporates the layout of the environment as well, so that they can locate objects in space."

The researchers say their experiment is more than a nifty trick: The fact that pigs can learn to use a mirror means they are capable of a type of awareness called assessment awareness, which means they can understand the significance of a situation in relation to themselves, over a short period of time. In this case, the pigs remembered how their own movements appeared in the mirror, and were able to apply that knowledge to a separate situation involving a hidden food bowl.

"Having a sense of self and using it is a form of assessment awareness," Broom wrote. Although the mirror experiment doesn't directly prove that pigs have a sense of self, the researchers suggest that given how quickly the pigs learn to recognize their own movements in a mirror, they may have some degree of self-awareness. "We have no conclusive evidence of a sense of self," Broom wrote, "but you might well conclude that it is likely from our results."

Other mirror tests have been used to more directly examine an animal's sense of self - if researchers apply a yellow mark to the black feathers of a magpie, for instance, the bird will use a mirror to clean itself off. Unfortunately, Broom says the mark experiments just don't work on pigs: Pigs are so accustomed to being streaked with mud, they don't much care if researchers apply extra marks on their bodies. "We have put marks on pigs," Broom wrote. "They take little notice of them."

Combined with a host of other research studies demonstrating the keen intelligence of pigs, the researchers hope their study will lead to better treatment of the farm animals. "If an animal is clever," Broom wrote, "it is less likely to be treated as if it is an object or a machine to produce food, and more likely to be considered as an individual of value in itself."

一只寻常的家养猪可以用五小时学会如何看懂镜子里的图像并用它找到隐藏的食物。

科学家认为使用镜子是一种复杂的认知过程，这是一定观察认知水平的象征。除了人类和一些灵长类动物，海豚，大象，喜鹊和一只叫Alex的着名的非洲灰鹦鹉也都能够通过使用镜子找到目标物或者除去它们身上的记号。看起来猪也是一种会使用镜子的生物，因为在五小时时间中，八只被研究的猪中有七只可以通过镜子反射找到隐藏的装有食物的碗。

"这是第一次对于猪使用镜子能力的展现，"来自哥伦比亚大学的动物行为专家Donald Broom在一封电子邮件中写道："对于动物具有复杂的学习和认知能力这一认识可能会改变人类看待物种的态度，并可能会带来长期的福利。"Broom合着了一篇这个月在《动物行为》发表的论文。

和大部分别的动物一样，猪也马上对研究人员放在猪圈里面发光的、会反射的东西表现出好奇心。它们慢慢靠近镜子直到鼻子碰到了镜面，然后查看镜子后面到底是什么。它们平均花了差不多20分钟注视镜中的自己，一直换不同的方向角度来观察。

"这种移动表明猪把自己身体的动作和镜中的影像联系在一起，然后学会这两者间的关联性。"来自利物浦大学的生物学家Louise Barrett 在一篇也是这个月发表在《动物行为》中的论文的评论中写道。

五小时过后，这些猪被安置在一个新的测试环境中，而一个装着食物的碗被藏在障碍物后面。猪不能直接看到碗，只可以通过镜子反射看到。碗上方的风扇使食物的香味在房间里流通，避免猪通过味道找到食物。

八只有观察镜子经验的猪中有七只看到了反射的碗并准确的找到了它的位置。它们并没有直接在镜子后面寻找，它们穿过了障碍物并准确直接的走到了放碗的位置。当研究者测试没有观察镜子经验的猪时，11只中有九只被镜子迷惑，在镜子后面寻找食物。

"这些结果表明猪不仅仅学会了它们自己的动作和镜中影像动作之间的关联，"Barrett写道，"它们也会把周围环境布局考虑在内，因而他们可以在一个空间中确认目标物的位置。"

研究人员说他们的实验不仅仅是一个俏皮的手法。猪会使用镜子的事实说明他们有一种评估认知，也就是说他们可以在短时间内理解环境和他们自身的关系。在这个实验中，猪记住了它们的行为是如何在镜子中呈现的，并能把这个经验应用到涉及隐藏的装有食物的碗这一独立事件中去。

"拥有自我意识并能应用是有评估认知的一种形式。"Broom写道。虽然镜子实验不能直接证明猪有自我意识，研究人员指出猪对于镜中它们自己身体移动认知的速度表明它们有一定的自我认知程度。"我们没有决定性的证据证明自我意识，"Broom写道，"但是你应该还是可以通过我们的结论推断这是可能的。"

其它镜子实验被用来更直接的检验动物的自我意识。比如，研究人员在一只黑色羽毛的喜鹊上涂上黄色记号，它能通过照镜子来擦掉记号。然而，Broom说记号实验不适用于猪：猪太习惯于身体涂上泥巴，它们并不太在意研究人员是否在它们身上涂上了多余的记号。"我们曾在猪身上涂记号，"Broom写道，"它们并不怎么在意这些记号。"

结合猪有智慧这些研究结果，研究人员希望他们的研究可以使得农场里的动物得到较好的对待。"如果一只动物是聪明的，"Broom写道，"它就不大会被看成一个东西或者制造食物的机器，它更会被看成有自我价值的独立个体。"