Social Behavior

Photo courtesy of Dominique Black

Mating system

The mating system of California sea lions is polygyny. It has been described as highly polygynous, moderately polygynous, as well as lek polygyny (Riedman, 1990; Renouf, 1991).

Territorial bulls are relatively inactive in courtship toward females, though the females do exhibit mate choice (Peterson, 1967). Females initiate courtship and copulation by displaying submissive postures in front of the male, and rarely breed more than once in a single season (B.E.C., 2004). Copulation has been observed on land, and in shallow and deep water (B.E.C., 2004; Peterson, 1967).

As discussed in the Social Spacing segment of this web page, California sea lions have mating only territories. These territories are maintained for 2-6 weeks and the bulls fast during this time. The territorial boundaries are fluid and unstable, but extend from land to deep water (Riedman, 2004). The preferred territories contain the largest amount of females and are controlled by the largest breeding bulls (male sea lions) (Riedman, 2004). To give an approximation of typical sex ratios during the breeding season, on San Nicolas Island, California the estimates are: pups 1:1, females to territorial males on rookeries 16:1, females to pups 2:1 (Ridgeway, 1981). Females give birth 1-2 days after arrival to the territory, and come into estrus is between 2 weeks and 28 days after the birth (Price, 2002; Riedman, 2004). Gestations is about 11 months, and implantation of blastocysts appears to be delayed (Riedman, 2004). Mothers are extremely aggressive shortly after birth (Peterson, 1967). Mothers make progressively longer trips to the sea to feed after their initial trip at 4 days after birth (Price, 2002; Riedman, 2004). Mother-pup relationships may persist for a year or longer, as lactation lasts several months (Ono, 1996; Riedman, 2004).

Here is a curious pup on one of the Galapagos Islands, though his mother is no where to be seen (probably out foraging). Photo courtesy of Molly Downey.

Why polygyny?

According to Peterson (1967), polygyny could have resulted of the production of a combination of interactions between (1) their amphibious habits, (2) the gregariousness of the females, (3) the aggressiveness of the males during the period of sexual activity, and (4) a basic pattern of reproductive physiology similar to most mammals, which permitted the exclusion of some males from the breeding population.

More specifically, there are hypotheses for certain characteristics evident in resource defense polygyny and male dominance (lek) polygyny in pinnipeds:

Resource defense polygyny:

Renouf (2001) suggests that there are four major features of a resource defense system: (1) territorial males arrive before females; (2) females become receptive in close proximity to where they give birth; (3) the rookery substrate is discontinuous; and (4) there may be a relatively low level of aggressive interactions among males.

(Relatively low level of aggressive activity in species exhibiting resource defense polygyny may reflect the ‘dear enemy’ phenomenon and the exclusion of non-territorial animals from the rookery area.)

Male dominance (lek) polygyny:

Bradbury (1981) suggests that there are four major features of classical lek systems: (1) there is no male parental care; (2) males aggregate at an arena to which females come to mate; (3) the display sites of males contain no critical resources required by females; and (4) females have an opportunity to select mates at the arena although the extent to which females have an opportunity to select mates is controversial.

Many species have leks which are intermediate between a resource defense system and classical leks (Bradbury, 1981). California sea lions may fall into this category. Males do not settle in their locations before the arrival of at least some females, and the locations of males that account for most copulation do not coincide with where most females give birth and care for their pups, suggesting that they do not exhibit resource defense polygyny. Females exhibit mate choice, suggesting lek polygyny, and males do not exert effort to control females. It is controversial as to whether California sea lions have male parental care as well as if there is a critical resource required by females where the males display, so these factors are difficult to sort into either type of polygyny.

Non-breeding season social interactions

During the non-breeding season (approximately August through April), the aggregations of sea lions on land have no stable social organization (Peterson, 1967). The same is also true on the hauling grounds (as contrasted with the rookeries) throughout the breeding season. However, there is a clear, size-related dominance relationship among non-breeders, regardless of sex (Peterson, 1967). The sight and sound of a larger animal often suppressed vocalization and movement by the male of the next smaller size, when a larger male was capable of physically attacking and punishing smaller males. When a small individual is approached or threatened by a larger one, the smaller usually yields by scrambling aside or running (Peterson, 1967). The hierarchical relations are weak and transient, but detectable in the non-breeding aggregation (Peterson, 1967).

Non-breeding individuals are always highly gregarious while on land. They often pack into congested groups, and they are strongly thigmotactic, which means they prefer squeezing into tight places where their backs and undersides make contact with other surfaces (Reidman, 1990). Therefore, they tend to keep their bodies pressed against each other as they sleep.

Parental Care

Here is a pup on one of the Galapagos Islands, curious of the human visitors. Photo courtesy of Dominique Black.

Mother to pup parental care is easily the most key social relationship within this species. Sea lion pups are among the most precocial of mammals; they have their eyes open at birth and within 10 to 15 minutes after delivery they can carry out highly coordinated motor activities (Peterson, 1967). However, mother-pup relationships may persist for a year or longer, as lactation lasts several months. Mothers make progressively longer trips to the sea to feed after their initial trip at 4 days after birth (Riedman, 2004). Females use a specific vocalization during the mother-pup recognition sequence, and pups make bleating mother-pup recognition vocalizations (B.E.C., 2004). The lactation period ranges from six months to a year, with females having longer lactation periods (Price, 2002). Females care for pups and yearlings simultaneously. California sea lions reach sexual maturity between four and five years of age (Price, 2002).

Alloparenting, which is common among pinnipeds, has been reported in California Sea Lions, but prevalence of occurrence is controversial (Price, 2002; Riedman1990). The term allomother describes a female that provides parental care for young that are not her own. This has been sometimes observed when females adopt and foster a pup that has been abandoned by its mother (Price, 2002). Single adult females have also been observed to watch over a group of young pups and "babysit" while other mothers are fishing (Wildelife, 2005). They are careful to keep the young pups out of deep water where they may be eaten by sharks. This female behavior is may be considered as reciprocal altruism. Some studies have shown that males also alloparent, as the bull watches out for his "family," of females and pups, by warning them of the presence of a nearby shark with barks, and even occasionally chasing away the intruder (Miller, 1971). However, the existence and frequency of this male behavior is also controversial (Barlows, 1972).

Why alloparent?

Individuals that care for another’s young may in fact derive selective advantages associated with the caring for genetically related young, called increased inclusive fitness. However, if the young is not related, it would seem that providing parental care for another’s young would be a disadvantage to the individual, as they expend unnecessary energy. If there are no genes of an individual being passed on to the offspring that it is caring for, there would seem to be no real benefit of doing so. Advantages of raising a non-related individual include parental experience, reciprocal altruism, and the exploitation (usually in primates) of the fostered young (Renouf, 2001). Therefore, California sea lions probably alloparent to gain parental experience and reciprocal altruism, such as baby sitting. Maternal errors involving cases of mistaken identity may be responsible for other cases of adoption.

In other pinnipeds, environmental constraints, such as a scarcity of breeding resources or food resources that require cooperative foraging strategies, also seem to have promoted the evolution of fostering behavior and parenting systems in which young are cared for communally (Riedman, 1990). Also, a shortage of breeding sites often results in the formation of high-density breeding colonies where mother-pup separations frequently occur (Renouf, 2001). The preponderance of orphaned pups and pup less females therefore set the stage for fostering behavior (Renouf, 2001).

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