How Smart Are Manatees?
These aquatic mammals are a study in contradictions

We tend to be impressed with fast-moving predators like hawks and social species like dolphins. But manatees have a relatively simple social structure and have not evolved with rapid, complex movements because they do not prey on other animals and are not themselves preyed upon. (Manatee photo © Walker Stanberry)

By Dr. Roger Reep

First of all, what do we mean by ‘smart’? The type of intelligence an animal possesses depends in part on what it senses through its vision, hearing, touch, smell and taste. Only then can thinking and behavior be organized in a meaningful way.

Click here to watch video showing the slow, relaxed movements of manatees. (MPEG format, 2 min.; courtesy of the U.S. Geological Survey, Sirenia Project)

We humans tend to be impressed by fast-moving predators like hawks, and social species like dolphins. Because manatees do not prey on other animals and are not themselves preyed upon, they have not evolved rapid, complex movements associated with these behaviors. Furthermore, they have a relatively simple social structure. Thus, they appear relaxed as they forage slowly for hours on abundant underwater vegetation and interact in small groups.

In addition, manatee brains have several unusual traits that have led some to assume they are unintelligent. But manatees are really just a study in contradictions. For starters, manatees have small brains in relation to their body size, and there is a long but misguided tradition of equating large brain size with greater intelligence. But the brain probably appears to be small in manatees due to the evolution of large body size to accommodate the very large gut needed to process all that food, and to provide for less loss of heat due to their low metabolic rate. So, rather than saying that manatees have relatively small brains, it is more accurate to say that manatees have relatively large bodies.

Although manatee brains are very smooth-surfaced for their size, the proportion of cerebral cortex -- the "wrinkled" part thought to be indicative of higher level functions -- is similar to other mammals with large brain sizes. (Images courtesy of the University of Wisconsin, University of Florida, and Michigan State University)
 

Secondly, manatee brains are very smooth-surfaced for their size, leading some to conclude that this lack of convolutions reflects a lack of adequate brain development. In 1902 one eminent scientist even compared manatee brains to the brains of human idiots!

Yet, the proportion of manatee brain composed of cerebral cortex (the “wrinkled” part of the brain thought to be indicative of higher level functions such as learning or memory) is similar to other mammals with large relative brain sizes and would seem to indicate a rich cognitive capacity.

It is very likely that our impression of manatees as perhaps not very smart reflects our inability to imagine the type of mental world created by a predominance of tactile sensation and sound over vision, as appears to be the case in manatees. As we learn more about their sensory abilities, their capacity to distinguish the vocalizations of other individuals, and their ability to learn and remember a variety of spatial and other information, it seems likely that our own appreciation of ‘smart’ will be expanded as well.

Dr. Reep is a Professor in the Department of Physiological Sciences at the University of Florida and a member of the SMC Board of Directors.

Rather than saying that manatees have relatively small brains, it is more accurate to say that manatees have relatively large bodies. (Photo © William Garvin)

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