SENSORY PROCESSES
Narwhals inhabit high Arctic areas, where they are seasonally exposed to extensive ice coverage with darkness prevailing in mid-winter and limited daylight for half of the year. As a result of the underwater icescape, narwhals must rely on acoustics for sensing their environment, navigating the pack-ice habitat, bathypelagic foraging, and communicating with conspecifics. Echolocation clicks and buzzes are used for social communication and serve the purpose of feeding, and calls. They listen to the echoes to form a reconstruction of their surroundings based on how those sound waves bounce off nearby prey or rock formations. According to this article, Narwhals Can 'See' Unlike Any Other Animal on Earth, "these clicks can be produced at a rate of up to 1,000 clicks per second, but cannot be perceived by the human ear. Their echoes are then detected by fleshy pads in the narwhals' lower jaws. The clicks are extremely directional, allowing them to home in on things like a flashlight." Echo reflection is also a method popularly used by all whales. Narwhals produce clicks to locate prey and obstacles at a short distance. These sounds are focused on their melons and regulated by musculature. Melons are round sensory organs in the heads of all toothed whales. They also produce bangs in order to incapacitate the prey which makes hunting an easier affair. Unless they are competing for a mate, whistles are rarely produced by narwhals.
Despite living in pristine environments with limited human activity, narwhals are greatly impacted by hunting. Narwhal habitats have been rendered more exposed to noise pollution due to the increase in ship traffic and the exploration of minerals.
As stated by Blackwell et al. (2018), early studies of narwhal sounds described the fundamental components of their vocal repertoire, i.e., clicks, burst pulses, and whistles. A few other studies have investigated behavioral aspects of the vocal repertoire, such as the possible use of "signature" calls, the vocal repertoire during the winter, and the possible relationship between call use and behavioral state. Buzzes are used during feeding by providing the whale with the fine-scale positional information needed over the last moments preceding prey capture. Non-feeding vocalizations are thought to serve communication during various social contexts, e.g., cohesion or recognition between individuals. Calls are also recorded in aggressive and agonistic interactions and between mothers and calves.
​​​
According to NAMMCO, a recent study in which a camera was attached to free-ranging narwhals demonstrated that narwhals spend a high proportion of their time upside down while diving and swimming at the sea bottom. This may allow them to better project their echolocation clicks to locate prey, and perhaps also to protect their lower jaw and tusk from contact with the bottom.
Figure 1. Echolocation of male indo-pacific bottlenose dolphins, similar to the narwhal. Retrieved from: https://www.researchgate.net/figure/Echolocation-of-male-indo-pacific-bottlenose-dolphins-Among-toothed-whales-captive_fig1_292615749.
TUSK
​
In fact, the only tooth these whales possess is their tusk. The tusk is a modified canine tooth and usually, only one tusk erupts from the left side of the upper jaw. However, in a small proportion of male narwhals, a second tusk erupts from the right side of the jaw. The role of the tusk has also been believed to be involved in feeding, but it cannot be obligatory since female groups are often segregated from the males during a large part of the year but are still able to obtain food.
Martin Nweeia et al. (2014) conducted a study that suggested that the tusk may have another function altogether as a sensory organ. The tusk is innervated and small channels in the tusk allow the inner, pulpy core of the tusk to come in contact with the marine environment. A tusked narwhal may therefore be able to directly sense changes in the marine environment, such as variations in salinity and temperature, through its tusk. This may aid in navigation as well as in avoiding being caught in rapidly freezing seas.
Researchers identified that "unlike most mammal teeth, the horn is not protected by enamel. Seawater enters the horn through cementum channels, which are also present in human teeth. The liquid then travels through a network of tubules to the center of the tooth. There, the water excites nerve endings in the pulp of the tooth, sending signals to the brain of the animal" (Maynard, 2014).​
Figure 9. Sensory model of the erupted male narwhal tusk. https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.22886