Recognizing one’s reflection is considered an advanced ability, and it’s only been confirmed in a handful of species, such as chimpanzees, orangutans, and dolphins.
“Snakes demonstrate many of the same cognitive and perceptual mechanisms as other animals if you study them in the right way, ask the right questions, and respect their biology and way of dealing with the world,” Burghardt says. (Read about 14 animals that have shown us how smart they are.)
In the study, published recently in the journal BehaviorBurghardt and colleagues studied 24 garter snakes born in a single litter in their Tennessee lab.
the snakes had been housed individually since birth and fed either an all-fish or all-worm diet, making it possible to differentiate the snakes’ faeces chemically.
When the snakes were four months old, the team exposed them individually to four different stimuli: their own dirty cage liner, the dirty cage liner from a same-sex sibling fed the same diet, the dirty cage liner from a same-sex sibling fed a different diet, and a clean cage liner.
During each experiment, the scientists measured the rate of each snake’s tongue-flicking and its overall movement around the cage. (In pictures: amazing amphibians.)
Snakes flicked their tongues less when exposed to the dirty cage liner from a littermate fed the same diet than they did to their own dirty cage liner.
Burghardt says this behavior shows that the garter snakes can recognize their own chemical cues as distinct from those of other snakes, even closely related snakes eating the same diet.
About 50 years ago, American psychologist Gordon Gallup and colleagues developed a mirror self-recognition test that is still the standard for many experimental studies.
Researchers put a mark somewhere on an animal’s body that it can only see in its mirror reflection. If the animal looks in the mirror and then touches or examines the mark on its body, it passes the test. People tend to pass the test as toddlers, and some great apes—chimpanzees, orangutans, and bonobos—recognize themselves. A select few non-primates, such as elephants and dolphins, may qualify as well.
But Gallup and his colleagues are skeptical of the evidence for mirror self-recognition in any species other than humans and great apes. They have also criticized non-visual self-recognition studies, such as those using odors or other chemicals, that purport to be equivalent to mirror tests.
That’s why one of Gallup’s frequent collaborators, psychologist James Anderson of Kyoto University, says that even though the snakes in Burghardt’s study may demonstrate chemical self-recognition, it’s not the same as an ape or human recognizing their appearance in a mirror.
“Many researchers overlook the spontaneity of great apes’ [and our own] use of mirrors simply to check on our appearance, perhaps to rearrange it or observe it from different viewpoints,” he said in an email. “No convincing demonstration exists of any so-called ‘chemical mirror’ being used in this way.”
Burghardt says, “I don’t make the claim that these snakes are self-conscious. But they seem to have an awareness of themselves as a different entity than another organism.”
Scientists are also divided about what an animal recognizing itself in the mirror really means in terms of cognition. Gallup and Anderson contend that passing the test is equated with self-awareness, self-consciousness, and possibly even the awareness of others’ unique selves.