Narwhals (Monodon monoceros) are really cool animals. This unicorn of the sea is found in the Arctic waters around Greenland, Russia and Canada, and is best known for its helical tusk that can be as long as 3 meters. All males have them, and some females also grow a horn, but research suggest that only about 15 % of the females get a horn.
A sketch of a narwhal. Image is Public Domain.
The tusk of the narwhal is not really a tusk or horn per se; it is in reality an elongated upper left canine tooth, the equivalent of the teeth you probably use when you want to break of parts of meat to eat (it's the one next to your four upper front teeth).
The narwhal is one of only two living members of the family Monodontidae (the other being the beluga whale). It can grow to be a little over 5 meters long, and weight over 1,500 kilograms.
It feeds mostly on benthic fish such as flatfish, but can also grab cob and halibut during the summer. To reach the sea floor they have been recorded of diving as far as 1,500 meters down in the sea, with dives that can last up to 25 minutes.
A group of narwhals. Image is Public Domain.
That was a very quick into to an incredible animal, and for the rest of the post we will take a closer look at the use of its “unicorn horn”, and how we have changed our theory about how and why it is used.
Why they have their characteristic horn
Charles Darwin apparently believed that the horn of the narwhal was a secondary sexual structure, much like the big feathers of the peacock. This means that the horns would be used to both attract females, as well as the likely aggressive combat between males.
Some biologists also went one step further with the combat theory, and suggested that the horns might be weapons that the males used as a spar to impale other narwhals during combat for females.
These theories sound very logical, and we see both these features in several other animals both on land and at sea.
Image is Public Domain.
Martin Nweeia from Harvard University recently published a vastly different hypothesis based from studying the anatomy of the tusk/horn. He and his research team believe that the tusk acts as a sensory organ that is mainly used for communication, and has nothing to do with combat at all.
First they figured out that the composition of the tusk is made of distinct layers, including a permeable outer layer that is used to channel seawater to the inner layer, and further to the central core that is full of nerve endings and blood vessels.
Knowing this the team took the research one step further and applied different types of water to the horn, and saw that the heart rate changed based on whether it was saline water or freshwater that was added. A higher salt concentration led to a higher heart rate, and essentially suggested that they are able "feel" the concentration of salt in the water.
Image is Public Domain.
While this information might not sound useful to us humans, it is very nice for narwhals and other animals who live in areas where there is a lot of change in the salinity of the water. A low salt concentration can tell the narwhal that the ice is melting in the area where the water is coming from, or a high salt concentration can tell it that there is no melting in progress.
The scientists goes as far as believing that this information can be shared among the males by touching the horns against each other, and thus telling the other whales where there is ice, and where the ice has already melted.
Not everyone accepts this theory
It is worth to keep in mind that this theory is not really commonly accepted, and many biologists believe it to be wrong, or at least incomplete. I guess you have to decide for yourself, but hopefully more research in the future will shed light on this debate.
The reason why a lot of people are skeptical is because of the study design of the research, where the heart rate was measured after the whale being caught by the research team. Some argue that this is what lead to the different heart rate when it was exposed to different concentrations of saline water. Other believe that while this might affect the heart rate to a certain effect, the evidence is still strong enough to be believable.
Another point that makes this theory a bit strange is that since only 15 % of the females grow a horn, these would have a clear advantage over the other females, which over time would lead to more females having them (due to natural selection favoring the horned females). And I agree that it does sound kind of strange that 85 % of the females are missing out on a very useful sensory organ.
There are probably many more narwhal secrets
The narwhals are really cool animals, but they spend most of their time hidden away under the ice that covers a lot of the Arctic sea. No one really knows a lot about the narwhals despite them being of ecological importance in the area, so I am sure we will see many interesting discoveries from this species as our technology allows us to study them even in the winter.
Thanks for reading
If you want to learn more about narwhals, then I suggest checking out narwhal.org. This website is ran by Dr. Martin T. Nweeia, the same person who lead the study that hypothesizes that the horn is in fact a sensory organ. This post at Harvard’s website is also worth checking out. Thanks for reading!
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