Hearing is one of the most important senses for a California sea lion.
Researchers believe that under water, a California sea lion can hear sounds in the range of 1 to 40 kHz, with a peak sensitivity of 15 to 30 kHz. California sea lions generally vocalize between 1 to 4 kHz. The average hearing range for humans is about 0.02 to 20 kHz.
Hearing in water is probably acute, with good directional ability.
In air, a California sea lion's hearing is probably slightly inferior to that of a human. California sea lions are more sensitive to airborne sounds than "true" seals (family Phocidae), but less sensitive than fur seals.
There is no evidence to support theories that sea lions have the ability to echolocate.
Underwater vision is acute. Like other pinnipeds, California sea lions have rounded lenses that allow their eyes to focus on light that is refracted upon entering water.
On land, California sea lions have good discrimination of bold outlines and rapid movements. Humans approaching too quickly will cause an alarm reaction.
A sea lion's eyes are very sensitive to changes in light intensities.
- The retina of the eye contains more light-gathering rod cells than cone cells, which discriminate color.
- California sea lions have a well-developed tapetum lucidum, a layer of reflecting plates behind the retina. These plates act as mirrors to reflect light back through the retina a second time, increasing the light-gathering ability of the rod cells. (The tapetum lucidum is the same structure that makes a cat's eyes appear to "glow" when reflecting light at night).
- In the water, a sea lion's eyes adapt easily to decreasing light levels; in the air, decreased light causes a dramatic decrease in visual acuity.
Recent studies show that sea lions can discriminate color in the blue-green spectrum; this is probably an adaptation for their aquatic environment.
California sea lions seek out physical contact with other sea lions. On land, California sea lions form groups, often touching and lying with each other.
A sea lion uses its sensitive vibrissae to explore objects on land and in the water. A nerve network transmits tactile information from the vibrissae to the brain.
Researchers believe that a sea lion's sense of taste is poorly developed.
The olfactory lobes of the pinniped brain are generally small; however, on land, smell is important in female-pup recognition and male recognition of estrous females. Sea lions may be able to detect a human by smell from hundreds of meters away.