Hearing
Baleen whales probably have well-developed hearing, which is valuable in the poorly lit ocean, where vision is less helpful.
A whale's ears are adapted for hearing underwater, not in air.
- The middle and inner ears of cetaceans follow a basic mammalian ear structure.
- A baleen whale has a small external ear opening on each side of the head. Each ear opening leads to a narrow auditory canal that is completely plugged by a waxy substance.
- Both bone and soft tissue are probably important in conducting sound to the ears.
The anatomy of the baleen whale ear is somewhat typical of an ear adapted to hear low-frequency sounds.
Eyesight
The lens of a marine mammal's eye is stronger than that of a land mammal.
In the eye of a land mammal, the cornea focuses light rays toward the lens, which further focuses the light rays onto the retina. Underwater, the cornea isn't able to adequately focus waves into the lens because the refractive index of water is similar to that of the interior of the eye.
The eye of a marine mammal compensates for this lack of refraction at the cornea interface by having a much stronger, spherical lens. It is more similar to the lens of a fish’s eye than the lens of a land mammal's eye.
In air, a marine mammal's eye compensates for the added refraction at the air-cornea interface. At least in bright light, constricting the pupil helps, but it doesn't fully explain how a whale achieves visual acuity in air. Research is ongoing.
The retina of a baleen whale's eyes contains mostly "rod cells", which are sensitive to low intensity light. "Cone cells", which distinguish between different colors and are most sensitive to bright light, are less abundant.
The tapetum lucidum is a reflective layer behind the retina. It reflects light back through the retina a second time, making the most of available light under low light conditions.
A whale's eyes are constantly bathed in water. There are no tear ducts, but glands at the outer cornea and eyelids secrete an oily substance that lubricates and cleans the eyes.
Tactile
The tactile sense has not been well studied in baleen whales, and the sensitivity of their skin is largely unknown.
Gray whales in certain breeding lagoons in Baja California, Mexico seem to seek out people and solicit interaction including touch. So far we do not have an accurate interpretation of this behavior.
Taste
The sense of taste has not been well studied in baleen whales, and whether they have any sort of taste reception is unknown.
Smell
Olfactory nerves and bulbs are present in baleen whales during the fetal stage, but they are greatly reduced in the adult brain. The sense of smell has not been well studied in baleen whales, and whether they have any sort of ability to smell is unknown.
