A California sea lion's primary means of communication is vocalization. Sea lions produce sounds both above and below water.
California sea lions are among the most vocal of all mammals. Vocalizations include barks, growls, and grunts.
During the breeding season, male California sea lions bark incessantly when establishing territories; once established, the males bark only when maintaining and defending their territories.
During periods of nonbreeding, submissive males become more vocal than dominant males.
Females use a specific vocalization during the mother-pup recognition sequence. This occurs when a female returns to the rookery after feeding to locate her pup. The female emits a loud trumpeting vocalization, which elicits a bleating response from her pup. This exchange continues until mother and pup find each other. Mother and pup also recognize each other by smell and sight.
Females become very aggressive immediately before and after giving birth. Their "threat vocals" progress from a bark to an intense squeal to a more forceful belch and finally to an irregular growl.
Pups make a bleating mother-pup recognition call and a high-pitched alarm call. They later develop an adult-like bark.