The mating system of this sea lion is polygynous. A male secures a breeding territory on the beach and actively defends it against other males though ritualized posturing and aggressive confrontation. The male leaves his territory to feed in the ocean for a few hours at a time. Upon his return, he may have to battle to regain his territory.
Males keep several females on their territories. If the female strays, the male will aggressively herd her back, sometimes entering another male's territory to do so. (Nowak, 1999)
Males have been seen killing pups, although presumably not their own. Defense of territories may be an indirect mechanism of paternal care for young.
There is some evidence of cooperative breeding (See Behavior) in which females care for pups other than their own.
Mating System: polygynous ; cooperative breeder
Australian sea lions have a breeding cycle of approximately 17.6 months. These non-annual cycles are affected by some unknown factor, not by environmental influence as previously thought (Higgins, 1993). Some females do not produce young in consecutive breeding seasons (Nowak, 1999). Births can occur over a period of 4-6 months in any colony of N. cinerea, making births highly unsynchronized.
When the breeding cycle begins, males copulate with harems of four or five females at a time (Ridgway, 1972). Males also have the ability to herd the females into mating groups, a feature rare in other species of sea lion (Riedman, 1990).
Females enter estrous about 6 days after giving birth, and are mated by the male at this time. There is some debate in the literature about the ensuing gestation period. Pinnipeds typically experience a delay in implantation of about three months, followed by an eight or nine month placentation. Because N. cinerea experiences a much longer interbirth interval, it is clear that this species differs from the typical pinniped pattern. Some investigators think that Australian sea lions experience a longer than average dely in implantation of the blastocyst, amounting to 10-11 months, and a normal length pregnancy (8-9 months). Others think there is a more typical pinniped length delay in implantation (5-6 months) and a longer than average placentation (over 12 months). (Nowak, 1999)
Young are typically weaned just before the birth of subsequent offspring, at 15-18 months. However, females have been seen nursing pups of different ages at the same time.
Breeding season: Because the breeding interval is oddly spaced, the breeding season steadily shifts throughout the calendar year.
Average number of offspring: 1.
Range gestation period: 512 to 576 days.
Range weaning age: 15 to 18 months.
Range age at sexual or reproductive maturity (female): 3 to 6 years.
Range age at sexual or reproductive maturity (male): 3 to 6 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous ; delayed implantation
Average birth mass: 7075 g.
Average number of offspring: 1.
Female N. cinerea come to shore about two days before they give birth in order to establish a natal site. After giving birth to a pup, the female will stay at the natal site for approximately 10 days before returning to the sea to forage. She will return to land every couple of days to nurse her young, staying with the pup for about 33 hours at a time. A mother uses both vocal and scent communication to locate and identify her pup.
As pups grow up, they often form small groups and swim in shallow rock pools before they venture into the ocean with their mothers.
Females care for their own young, nursing them until about 26 days before giving birth to their next pup. Some mothers have been seen nursing both a yearling and a newborn pup. There are reports of females being aggressive to pups other than their own, but there are also some reports of females taking care of groups of pups. This makes it difficult to determine how much cooperative care of young there might actually be, although it is clear that some cooperative care occurs. Altricial at birth, pups are able to follow their mothers both on land and into the sea at approximately 3 months of age.
No specific male parental care has been reported for N. cinerea, but by maintaining territories, fathers may protect their offspring from other males of the species.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)
- Nowak, R. 1999. Walker's Mammals of the World. Baltimore: The Johns Hopkins University Press.
- Ridgway, S. 1972. Mammals of the Sea: Biology and Medicine. IL: Charles C. Thomas.
- Riedman, M. 1990. The Pinnepeds: Seals, Sea Lions, and Walruses. CA: University of California Press.