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."

    一只尋常的家養豬可以用五小時學會如何看懂鏡子里的圖像并用它找到隱藏的食物。

    科學家認為使用鏡子是一種復雜的認知過程，這是一定觀察認知水平的象征。除了人類和一些靈長類動物，海豚，大象，喜鵲和一只叫Alex的著名的非洲灰鸚鵡也都能夠通過使用鏡子找到目標物或者除去它們身上的記號。看起來豬也是一種會使用鏡子的生物，因為在五小時時間中，八只被研究的豬中有七只可以通過鏡子反射找到隱藏的裝有食物的碗。

    "這是第一次對于豬使用鏡子能力的展現，"來自哥倫比亞大學的動物行為專家Donald Broom在一封電子郵件中寫道："對于動物具有復雜的學習和認知能力這一認識可能會改變人類看待物種的態度，并可能會帶來長期的福利。"Broom合著了一篇這個月在《動物行為》發表的論文。

    和大部分別的動物一樣，豬也馬上對研究人員放在豬圈里面發光的、會反射的東西表現出好奇心。它們慢慢靠近鏡子直到鼻子碰到了鏡面，然后查看鏡子后面到底是什么。它們平均花了差不多20分鐘注視鏡中的自己，一直換不同的方向角度來觀察。

    "這種移動表明豬把自己身體的動作和鏡中的影像聯系在一起，然后學會這兩者間的關聯性。"來自利物浦大學的生物學家Louise Barrett 在一篇也是這個月發表在《動物行為》中的論文的評論中寫道。

    五小時過后，這些豬被安置在一個新的測試環境中，而一個裝著食物的碗被藏在障礙物后面。豬不能直接看到碗，只可以通過鏡子反射看到。碗上方的風扇使食物的香味在房間里流通，避免豬通過味道找到食物。

    八只有觀察鏡子經驗的豬中有七只看到了反射的碗并準確的找到了它的位置。它們并沒有直接在鏡子后面尋找，它們穿過了障礙物并準確直接的走到了放碗的位置。當研究者測試沒有觀察鏡子經驗的豬時，11只中有九只被鏡子迷惑，在鏡子后面尋找食物。

    "這些結果表明豬不僅僅學會了它們自己的動作和鏡中影像動作之間的關聯，"Barrett寫道，"它們也會把周圍環境布局考慮在內，因而他們可以在一個空間中確認目標物的位置。"

    研究人員說他們的實驗不僅僅是一個俏皮的手法。豬會使用鏡子的事實說明他們有一種評估認知，也就是說他們可以在短時間內理解環境和他們自身的關系。在這個實驗中，豬記住了它們的行為是如何在鏡子中呈現的，并能把這個經驗應用到涉及隱藏的裝有食物的碗這一獨立事件中去。

    "擁有自我意識并能應用是有評估認知的一種形式。"Broom寫道。雖然鏡子實驗不能直接證明豬有自我意識，研究人員指出豬對于鏡中它們自己身體移動認知的速度表明它們有一定的自我認知程度。"我們沒有決定性的證據證明自我意識，"Broom寫道，"但是你應該還是可以通過我們的結論推斷這是可能的。"

    其它鏡子實驗被用來更直接的檢驗動物的自我意識。比如，研究人員在一只黑色羽毛的喜鵲上涂上黃色記號，它能通過照鏡子來擦掉記號。然而，Broom說記號實驗不適用于豬：豬太習慣于身體涂上泥巴，它們并不太在意研究人員是否在它們身上涂上了多余的記號。"我們曾在豬身上涂記號，"Broom寫道，"它們并不怎么在意這些記號。"

    結合豬有智慧這些研究結果，研究人員希望他們的研究可以使得農場里的動物得到較好的對待。"如果一只動物是聰明的，"Broom寫道，"它就不大會被看成一個東西或者制造食物的機器，它更會被看成有自我價值的獨立個體。"