Should you meet a turtle basking on a log in the sun, you might reasonably conclude that the turtle is in a good mood.
Granted, there has been little scientific evidence that reptiles experience such emotional richness -- until now, at least. Researchers in England identified what they describe as "mood states" -- emotional experiences that are more than momentary -- in red-footed tortoises by administering tests that use responses to ambiguity as windows into the psyche. The results of the study, published in the journal Animal Cognition in June, could apply to many more reptiles and have profound implications for how people treat them.
"There was an acceptance that reptiles could do these short-term emotions," said Oliver Burman, who studies animal behavior at the University of Lincoln in England and is an author of the paper. "They could respond to positive things and unpleasant things. But the long-term mood states are really important." As for why it took so long to show this in reptiles, Burman said, "maybe we just haven't asked them correctly."
Reptiles have a long-standing reputation as being unintelligent. Writing in 1892, Charles Henry Turner, the pioneering comparative psychologist, described reptiles as "intellectual dwarfs." Eight decades later, in 1973, prominent scientists were referring to them as "reflex machines" and (in a paper titled "The Evolutionary Advantages of Being Stupid") as possessing "a very small brain which does not function vigorously."
Burman is among the scientists responsible for what some have called a "reptilian renaissance." An array of findings -- tortoises learning from one another, snakes with social networks, crocodiles displaying complex communication -- indicate that reptiles are no less brainy than mammals and birds.
But do they have moods?
Burman and his colleagues approached that question using what is known as a cognitive bias test. These operate on a principle common to many animal minds, human and nonhuman alike: Individuals in a good mood are more optimistic about uncertain outcomes, whereas those in a bad mood tend to be pessimistic.
The researchers placed each of 15 tortoises inside an enclosure with two empty bowls set on the floor. When a tortoise approached one of the bowls, it received a helping of arugula, a favorite treat. When it approached the other bowl, it received nothing. After the tortoises had learned to associate each location with a reward or the lack thereof, the researchers placed three additional bowls at intermediate points between the original bowls. The speed, relatively speaking, with which a tortoise investigated these new, ambiguously placed bowls served as a proxy for its emotional state.
Then, over a period of two weeks, the researchers presented each tortoise with an unfamiliar object -- a coaster made of beads -- and put the tortoise in an enclosure with walls and a floor covered in patterns it had not previously encountered. Such novelties are known to make tortoises anxious, but the tortoises that were most optimistic in the earlier test showed the least anxiety in this one. (A tortoise extends its head when it is relaxed; the farther the extension, the less anxious it is likely to be.) They appeared to be buffered by their good moods.
"These results significantly extend contemporary knowledge of the capacity for reptiles to experience mood states," Burman and his colleagues wrote in the paper. They noted that the results echoed those of a similarly designed 2010 study on dogs experiencing separation anxiety.
How broadly can the new findings be extrapolated to other reptiles? "We can't say for sure, but evidence of a capacity within the group tells us that it can exist," said Anna Wilkinson, a reptile cognition specialist at the University of Lincoln and an author of the study. "We need to test other groups of reptiles."
On a Facebook group devoted to reptiles and amphibians, some underwhelmed members remarked that scientists had merely discovered what reptile owners already knew. But Gordon Burghardt, a comparative psychologist at the University of Tennessee, Knoxville, and pioneer in the study of reptile intelligence, noted the value of empirical demonstration. "Experimental evidence is important," said Burghardt, who was not involved in the study.
Asked whether he thought that many and perhaps even all reptiles experienced moods, Burghardt replied, "Certainly."