The paper: Ari, C., & Agostino, D. P. D. (2016). Contingency checking and self-directed behaviors in giant manta rays : Do elasmobranchs have self-awareness ? Journal of Ethology, 34(2), 167–174. doi:10.1007/s10164-016-0462-z.
When you look into a mirror, you know you are looking at your reflection; anything you do -wink, smile, frown- will be replicated by the image looking back at you. It may seem obvious to us, but understanding that mirrors show us our own reflection, and not another person, has been considered a proxy for self-awareness, or understanding our place in the world as an individual. Very few non-human animals have been shown to grasp this concept. Only chimpanzees, orangutans, bonobos, elephants, dolphins, orcas, and magpies have passed what is known as “the mirror test”, suggesting some level of self-awareness. But most of those animals shouldn’t surprise you – apes are our closest relatives, dolphins have long been characterized as one of the most intelligent animals, and even magpies are notoriously inquisitive. But what if someone told you that a species of fish might soon be added to that list?
Manta rays (Figure 1) are a type of cartilaginous fish that filter feed on zooplankton using their cephalic fins to funnel water into their mouths (Figure 2). They frequently form large cooperative feeding groups, which suggests that they have complex social structure. Manta rays also have the largest brains and largest relative brain mass (weight of brain relative to body size) of any fish species. With over 30,000 species to compete with, that is a pretty remarkable feat! Furthermore, manta ray brains are rather complex, indicating a high level of cognition. This has prompted researchers to test the bounds of their brain power to see if manta rays possessed a sense of self-awareness.
How can you tell if an animal is self-aware: The Mirror Test
Since the 1970’s researchers have used the mirror test to determine if an animal is self-aware; that is to say that the animal can recognize itself as an individual. Here’s the run down (pet owners, feel free to test it out on your own pets!): you put an animal in front of a mirror – does the animal behave differently towards the reflection than it does towards other animals (conspecifics)? Animals that are not self-aware tend to display acts of aggression or affection towards the reflections whereas animals that are self-aware tend to test out the mirror by performing unusual behaviors in front of it. This can include repeatedly sticking out their tongue or blowing bubbles to see if the reflection does the same thing at the same time (called a “contingency check”) or examining places on their body they can’t usually see (called a “self directed behavior”).
The next test in the series is usually “the spot test”. Discretely put a spot on the animal’s body. An animal is considered “self-aware” if upon seeing the spot on the reflection, they touch the spot on their own body, not on the mirror. Essentially, if you see a smudge on your cheek, you understand that it is your own face and go towards your face (not the reflection in the mirror) to remove the smudge. Although it is not foolproof, this method has been the bench mark for studying if animals are self-aware and has allowed us to better understand animal cognition. For more examples on how this test works, watch this video.
Mirror Test on Manta Rays
To test the possibility that manta rays are in fact self-aware, researchers implemented the mirror test on two manta rays at the Atlantis Aquarium in the Bahamas. A large mirror was lowered into the manta ray tank and individuals were observed for 10 – 50 minutes. During this time, researchers recorded behaviors and categorized them as social (closely interacting with one another – not with the mirror), feeding, and behaviors that appeared to indicate some sort of self-awareness : contingency checking (i.e. unusual/repeated behaviors while in front of the mirror) or self-directed behavior (examining parts of the body not normally visible to the individual while in front of the mirror). To make sure that manta ray behaviors were in response to the mirror, control trials were also performed with the mirror out of the water and with a similar-sized, non-reflective white board placed in the tank instead of the mirror.
Do you see what I see?
When the mirror was in the water, the manta rays spent significantly more time in the observation area than they did when there was no mirror or
when the white board was in place (Figure 3a), suggesting that the mantas were interested in the reflective mirror – and not just novel objects in the tank (represented by the white board control).
Not only did the manta rays spend more time in the area, but when in front of the mirror they also performed some unusual behaviors. When the mirror was in the water, the mantas were frequently seen circling the tank to swim towards the mirror (Figure 3b). When in front of the mirror, they would frequently open and close their cephalic fins (Figure 3c) or blow bubbles- a novel behavior only seen in front of the mirror. Manta rays were also seen exposing their bellies to the mirror in a manner that could have been a self-directed behavior for inspecting that region of their body. Neither of the two manta rays displayed traditional aggressive or social behaviors towards the reflection.
Are Manta Rays Self Aware?
This is only the first step in answering this intriguing question. The researchers would like to perform a spot test (see above) on the manta rays to see if they can be added to the list of species that have “passed” the test, thereby joining the ranks of species considered to be self-aware. The mirror and spot tests do not definitively prove that an animal is, or is not, self-aware but this experiment has definitely left researchers thinking about manta ray cognition. Who knows what researchers will reveal next about the way manta rays and other fishes are able to think!
For more information on manta rays and conservation efforts for the species follow the links below: