Roosters (公鸡) act differently when faced with another chicken rather than just their own reflection. This may mean that the birds can recognize themselves in a mirror, a key indicator of self-awareness. In the traditional mirror self-recognition test, which originated in 1970, researchers place a mark on an animal's body in a spot that it only see when seeing its reflection. They note if the animal touches the mark while examining its mirror image, which suggests it understands that what it sees represents its own body. Few non-human species have passed this test, but they include some great apes, dolphins, elephants.
However, results from the test are often variable. Sonja Hillemacher and her colleagues from the University of Bonn in Germany wondered if this was because there is little natural reason for many animals to find out such marks. So, they have tried to adapt the test to the natural behaviour of roosters. Roosters usually make loud noises to warn other chickens when they see predators (捕食者) but generally stay quiet when they are alone.
In the lab, they tested 68 roosters one by one in an arena divided by a wire net. They placed a bird on one side, and either left the other side empty or put another rooster in it. Then they added a mirror to the divider for some tests. The results showed that when a rooster was paired with another rooster, it raised the alarm more often than when it was alone, regardless of whether it could see its own reflection. When another rooster was present but hidden behind a mirror, few alarms were raised, showing that roosters can distinguish between reflection and reality through vision rather than smell or sound.
Since the birds acted similarly when alone and with a reflection, they may realise their reflection is of themselves, say the researchers. While the research suggests that roosters may recognize themselves in mirrors, it is too early to claim that chickens possess this ability.