You often see sea lions resting quietly on the surface of the water in "rafts" of several animals, heads and flippers poking above the water. By waving a flipper in the air, they absorb heat from the sun and avoid losing heat to the water.
Groups of sea lions can be very noisy; their constant, piercing barking can be heard from a quite a distance.
Although once depleted, California sea lion populations have rebounded due to the protections afforded by the Marine Mammal Protection Act. Of the five species of sea lions worldwide, the California sea lion is the only one whose population is expanding. Other species are either in decline or limited to very small populations (less than 10,000).
Sea lions often body surf.
Sea lions stick their flippers out of the water to regulate their body temperature.