Male southern elephant seals arrive at breeding grounds several weeks before females and, through vocalizations, body positions, and occasional fighting, claim territories on the beach. The best and largest territories go to the largest and strongest males. These “alpha” males become the head of a harem when the females arrive, often mating with up to 60 females in their harem. If harems exceed this size, additional “beta” males may be present, each claiming as many females as they can. Females become a part of a harem simply through their position on the beach and may move from one harem to another incidentally.

In addition to their mating duties, alpha males are responsible for keeping unwanted males away from the harems. This is done through the same vocalizations and aggressive body postures that were used originally to claim their harem. Males must remain on their territory to defend it and, therefore, go for periods of months without eating. This, and the stress of aggressive encounters with other males and the energy expense of mating with multiple females, can take a significant toll on male physical condition. Only males in the best physical condition at the beginning of breeding season will successfully defend their territory and breed with multiple females. Subordinate males attempt to copulate with females on the edges of territories or in the surf as they leave the beach.

Females that were pregnant from the previous year’s mating give birth to one pup shortly after arriving on land. A period of lactation follows the birth. Then, several days before the pups are weaned from their mother’s milk, females enter estrus and mate with the alpha male or a successful beta male. Shortly following mating, males return to sea. Females return to the sea immediately after the pups are weaned. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Baldi et al., 1996; Englehard et al., 2002; ESRG - Filippo Galimberti and Simona Sanvito, 2002; Galimberti, Fabiani, and Boitani, 2003; Gaskin, 1972; Le Boeuf and Petrinovich, 1974; McCann, 1980; McCann, 1982; Nowak, 2003; Seal Conservation Society, 2001; Slip and Clippingdale, 2002)

Once a year, from August to November, southern elephant seals return to land to breed. Amazingly, most return to the very same breeding grounds on which they were born. Five to seven days after pregnant females arrive on the beaches, they give birth to one pup. Occasionally twin pups are born but one typically dies soon afterwards. The mothers then nurse their young for about 23 days. Females may nurse longer if their energy reserves allow them to do so. During their time on the breeding grounds females eat little or not at all. Towards the end of this time, females enter estrus and mate with a male. Shortly after mating, females wean their young. At this point, they abandon their young and return to the ocean. Pups then forage on their own for several weeks before venturing out to sea in small groups. Female southern elephant seals typically reach sexual maturity by the age of 3 and participate in the annual breeding cycle by age 6. Males reach sexual maturity by age 5 or 6, but rarely are developed enough to compete for mates until they reach 10 to 12 years of age. The gestation period of female M. leonina is about eight months. There is a period of several weeks during late October when all mature females mate. In order to maintain the yearly birthing cycle with an eight-month gestation period, there is delayed implantation of the fertilized egg for about three months. After the three-month delay, the egg implants and begins to develop to become mature enough for birth during the next breeding season. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Englehard et al., 2002; ESRG - Filippo Galimberti and Simona Sanvito, 2002; Gaskin, 1972; Le Boeuf and Petrinovich, 1974; McCann, 1980; McConell et al., 2002; Nowak, 2003; Seal Conservation Society, 2001; Slip and Clippingdale, 2002; Van Der Toorn, 1999)

Female southern elephant seals are the sole caregivers for their young from the moment of conception until weaning, a period that lasts around one year. After delayed implantation, which follows mating, the nine-month gestation period of the pregnancy begins. During this time, the pup develops inside the mother as she is diving and feeding in sub-Antarctic waters. Shortly after coming to land, females give birth to their pups, typically weighing between 25 and 50 kg at birth. Following birth, mothers bond vocally and through smell with their pup. For the next 20 to 25 days (sometimes as long as 35 days) mothers are responsible for providing milk and protecting pups. Mothers are typically less than one-meter from their pups during the stage of suckling, regardless of tide, the position in the harem, or the time in the breeding season. A pup might get separated from its mother due to male harassment and herding of females. This can result in an abandoned pup. Once a pup is separated from its mother the results are fatal. Alien suckling (nursing between unrelated cows and pups) isn't tolerated in this species. If an orphan pup attempts to steal milk from a sleeping or resting cow, it usually is bitten and will succumb to starvation or the effects of the bites. The most dire threat to young pups is adult males who crush pups as they travel and fight on beach territories. During lactation, mothers do not return to the water to feed and instead live on fat reserves built up during the previous foraging season. At weaning pups weigh from 120 to 130 kg, a weight gain of as much as 105 kg in a few weeks! ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Baldi et al., 1996; Englehard et al., 2002; ESRG - Filippo Galimberti and Simona Sanvito, 2002; Gaskin, 1972; Hindell et al., 1999; McCann, 1980; McCann, 1982; McConell et al., 2002; Nowak, 2003; Seal Conservation Society, 2001; Slip and Clippingdale, 2002)

Immediately following weaning, female southern elephant seals return to sea, leaving their pups alone on the beach. Eventually the pups begin to get hungry and find their way to the ocean, learning to feed and swim on their own. After weaning, there is no interaction between parents and pups. Approximately 30% of these pups will not live through their first year. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Baldi et al., 1996; Englehard et al., 2002; ESRG - Filippo Galimberti and Simona Sanvito, 2002; Gaskin, 1972; Hindell et al., 1999; McCann, 1980; McCann, 1982; McConell et al., 2002; Nowak, 2003; Seal Conservation Society, 2001; Slip and Clippingdale, 2002)