The killer whales’ eyes are not visible, almost secret. Each eye is situated behind the mouth opening, in front and below the white temporal mark. The eye also has an eyelid which main function is to lubricate the cornea in order to avoid saline corrosion (salt is very corrosive). This lubrication is done thanks to the lachrymal glands, very developed and secreting oily tears.

The eye is flattened from front to back at the detriment of the anterior chamber. The pupil is large to compensate the strong luminosity contrast. Wide open, it picks up a large quantity of light, allowing the animal to see in a darker environment. Outside water or close to the top the pupil is reduced to a thin slit to avoid being blinded by the light. The most external layer, the sclerotic, is very thick in order to resist the pressure during deep dives. The crystalline lens is nearly spheroidal. The choroids membrane, situated at the front of the retina, is highly vascular. The retina is also highly vascular; except for an avascular horizontal band, situated above the papilla) (beginning of the optic nerve), it is rich in rods. The optic nerves are well developed. All their fibres suffer decussating. Which means that absolutely ALL the optic nerve fibres are sent to the opposite hemisphere (in most mammals, the majority is sent). There is a total decussating with the orcas. Unlike some cetacean, the killer whale muscles are quite developed which allows a quick misshaping of the eye curve, adapting it rapidly from an underwater environment to an external one and vice versa. The orca’s eyesight is good in and out of water (which is unusual). It is an important hunting element when the animal is in “spying” position (prey observation outside the water, the head is above the water and the rest of the body nearly vertical in the water).

The eyelids have no tarsal cartilage, or eyelashes, or Meibomian Glands. Unlike a lot of cetaceans, the killer whales have mobile eyelids (as the delphinidae generally). These mobile eyelids aim at lubricating and protecting the eyes from the saline attacks. The lachrymal glands and the Harder eye gland, which are very developed, generate an oily substance recovering the cornea and the conjunctiva. So the eyes are protected from seawater, a very corrosive element.

If the eyesight is good, unfortunately it is monocular. Hence the animal sees mainly sideway and need to move to the side for a better vision. To palliate this problem, the eye moves very quickly to gain a larger field of vision. There is a certain form of binocular vision but it’s limited to the front (close to the mouth). It is important to highlight that the eyes are independent from each other (one can see at the front and the other will see at the back, but one at a time).

But can orcas see in the dark? Since the deeper the darker, to the point of total darkness…
As we previously mentioned, a larger opening of the pupil allows more light caption. However, without sufficient light, the pupil is useless. Yet, the orcas, dreadful predators, move in the dark as well as troubled waters!!!

It is therefore another ultra sophisticated system that will take on the navigation and chase with which the orcas will be able to find its ways, the ECHOLOCATION.

Slight details, if you meet up with a killer whale (lucky devils) swimming at slow pace and eyelid shut… it’s asleep.

If the killer whale can see well, it can hear even better. Actually it’s its whole motion, communication and attack systems that are based on emissions and receptions of sound waves.

Killer whales’ hearing system is therefore very developed, and is sensitive to frequencies comprised between 500 hertz (Hz) and 105 kilohertz (which is 105 000 Hz, 105kHz). Itself, the animal will emit sounds comprised between 100 Hz and 40kHz. It is thought that the low frequencies transmitted, although inaudible by them, are used to hunt or for its enemy…

Language is in a frequency around 15-20kHz. The highest frequencies are used for the echolocation.

If Jacques-Yves Cousteau called the oceans “the world of silence”, it’s because human did not realise how much noise there was (although it could hear it). The average audible frequency underwater is 10kHz.

The auditory orifice is situated in the extension of the jaws as the inferior area of the animal mouth picks up the echolocation waves.

Orcas have evolved a great deal through time. The brain area dedicated to hearing has developed a lot, more than the area dedicated to the eyesight. The external pavilions have disappeared totally and the external conduit opens thanks to a simple orifice at the skin level. The ears have become a mere conduit with a diameter the size of a needle hole. This tube has lost its auditory function to become a barometer, needed for the atmospheric pressure calculations. The conduit becomes larger as it reaches the tympanic area. The said tympanic membrane is curved on the external side and is in contact with the hammer via a muscle. Like humans, the hammer is linked to the anvil, itself linked to the stirrup. These last 3 are quite bulky and isolated so they can resist high pressure. The joints between the ossicles are stiff. This layout allows an easier passing through of the high frequencies, especially the language’s 15-20kHz. The tympanic bubble is wrapped up in adipose tissues that become elastic fibrous tissues, recovered by a thick tissue, hollow with air filled cavities.

The ear is hence wrapped up in a thick tissue full of air bubbles whose function is to reduce or muffle the frequencies in order to minimise sound interference or resonance (like a recording studio). Noises are then transmitted to the cochlea (sound amplification) and then to the auditive nerve to be analysed

The ear is not directly used for echolocation. It’s the inferior jaw, hollow like a flute, which will receive these waves and will transfer them to the other reception organs…

The auditory area in the brain is exceptionally large, which confirm that orcas have a sonorous and vibratory stimuli environment.

Comme nous l'avons vu, l'orque a perdu son odorat, trop rarement sollicité... Néanmoins, la zone olfactive du cortex est toujours existante. Ce n'est donc plus qu'une trace ancestrale...