In water, over tens of metres deep, the light is so weak that it is impossible to rely on the eye sight to move around. When divers can use artificial light, orcas have a much more sophisticated system to visualise their environment, even without any light. This incredible device is called ECHOLOCATION. The principle is simple and extremely complex at the same time. Schematically, the killer whale will produce a high frequency sound to the front. This sound will then spread and meet with an obstacle (or a prey). An echo phenomenon happens which means that the frequency transmitted will be blocked and will have no other way to go than come back. Because of the irregular contact with the obstacle, the return frequency will be modified. It will then be picked up and decoded by the animal who will create a virtual image of the obstacle. This echolocation system is also known as SONAR.

In the aquatic environment, the sound is of vital importance. Outside water the sound travels at about 340m per second when in water, the same sound will travel at …. 1500m per second. Which is 5 times faster. It now becomes clear why marine animals use it so much! Obviously, this speed will vary according to different criteria, which are the water temperature (4.5m/s per degree C), the salinity of the water (1.3m/s per salinity unit) and the depth (16m/s per 1000 m). The killer whale usually dives at about 300m so the latter will have less influence. The speed is therefore very high. These transmitted sounds act like virtual eyes able to give a clear image at several, up to tens of, kilometres. The sonar principle is one of the common characteristics the odontoceti have. But let’s have a closer look at how it works…

To visualise its environment, a killer whale will need to create sounds and interpret them when they come back. As a result, the system is made of a transmitter and a receiver. In fact, everything starts next to the blowhole, or to be more precise, under the blowhole. There, is found 6 small pockets called aerial bags, they are divided as follows; 2 vestibular bags, 2 accessory bags and finally 2 pre maxilla bags (each time 1 on each side on the longitudinal cut). These 3 pairs of bags are the sound transmitters. They are filled with air that the orca is going to use as a wind instrument, transferring the air from one bag to the other via openings that the killer whale warbles at will, thus producing sounds at very high frequencies. However, to have an efficient echolocation these frequencies must be sent in the same direction. The bony surfaces have this most important role. The bony surface of the skull, close to the nasal cavity, will send these frequencies back to the front, making it impossible for a backward transmission. These frequencies will then arrive to the MELON, either directly or after having been sent back from the bony surface to the superior jaw. Here the melon plays a crucial role of acoustic lens. The sound will be focused and sent very precisely towards a given target.

Actually, there are 2 kinds of frequencies sent for the echolocation; a high frequency and a low frequency. The high frequency gives a very precise and rich image as it can transport more information. Unfortunately, its range is much shorter. So the killer whale will combine high and low frequencies to evolve. It first sends a low frequency transmission in order to analyse its environment, such as depth, obstacles, and profile of the bottom of the sea. This will allow the animal to virtually create the environment. If it receives an abnormal or unusual echo, it will increase the frequency while getting near to define the problem better. To do so, it will sweep with its head the area to control. Finally it will send high frequency in order to have a detailed picture of the shape, but most of all of the internal structure of the object. It can, in effect, differentiate between 2 objects visually identical but with different density. It can also see what is inside a hermetical box… Much more than a third eye, it is a scanner.

All is left now, is to gather the information back and analyse it …

The ear, via the ear canal, will then receive the sounds. This ear is phonetically insulated by the eardrum bubbles compact and bony (situated in the skull cavity) and by a mucous and fat layer. This to allow the treatment of a sound transmitted by the ear canal only, which means without parasite noises. However, it is not there that the information will be collected. There is actually an area much more sensitive to the sounds. It’s actually the inferior maxilla and the ears (middle and internal zone) that form the receptor. The waves reach the rostrum extremity, the lips being very sensitive, travel then in a very thin fat layer along the inferior maxilla to arrive eventually in the internal ear, via the jaws articulation. All this information received will now be treated. In order to do so, the information will be sent, thanks to the acoustic nerve (very developed and also called the auditory nerve) to a specific area of the cortex (also very developed). This process allows the restitution of a virtual image of the environment.

Obviously, all of these are going to happen at a great speed, as the killer whale has to move, hunt, … fast. Note that the echolocation frequency is about 16 to 20 kilohertz (kHz) and for an about 210-microsecond duration. The frequency above 15 kHz (language) is normally dedicated to the echolocation.

The language is created by the rear (and deep) area of the larynx. These sounds are used for communication, hunting techniques, the alert state, and also the sexual excitation. The frequency of these signals is closed to 15 kHz and therefore especially sensitive to the ear…