Northern Elephant Seal - Social Behavior and Reproduction

Social Behavior and Reproduction

Northern elephant seals return to their terrestrial breeding ground in December and January, with the bulls arriving first. The bulls haul out on isolated or otherwise protected beaches, typically on islands or very remote mainland locations. It is important that these beach areas offer protection from the winter storms and high surf wave action. The bulls engage in fights of supremacy to determine which few bulls will achieve a harem.

After the males have arrived the beach, the females arrive to give birth. Females fast for five weeks and nurse their single pup for four weeks; in last few days of lactation, females come into estrus and mate. In this polygynous society, a high-ranking bull can have a harem of 30–100 cows, depending on his size and strength. Males unable to establish harems will wait on the periphery, and will try to mount nearby females. Dominant bulls will disrupt copulations of lower-ranking bulls. They can mount females without inference, but commonly break off to chase off rivals. While fights are not usually to the death, they are brutal and often with significant bloodshed and injury; however, in many cases of mismatched opponents, the younger, less capable males are simply chased away, often to upland dunes. In a lifetime, a successful bull could easily sire over 500 pups. Most copulations in a breeding colony are done by only a small number of males and the rest may never be able to mate with a female. Pups are sometimes crushed during battles between bulls.

After arrival on shore, males fast for three months, and females fast for five weeks during mating and when nursing their pups. The gestation period is about 11 months. Sometimes, a female can become very aggressive after giving birth and will defend her pup from other females. Such aggression is more common in crowded beaches. While most females nurse their own pups and reject nursings from alien pups, some do accept alien pups with their own. An orphaned pup may try to find another female to suckle and some are adopted, at least on Año Nuevo Island. Pups nurse about four weeks and are weaned abruptly approximately two months before being abandoned by their mother. Left alone, weaned pups will gather into groups and stay on shore for 12 more weeks. The pups learn how to swim in the surf and eventually swim farther to forage. Thus, their first long journey at sea begins.

Elephant seals communicate though various means. Males will threaten each other with the snort, a sound caused by expelling air though their probosces, and the clap-trap, a loud, clapping sound comparable to the sound of a diesel engine. Pups will vocalize when stressed or when prodding their mothers to allow them to suckle. Females make an unpulsed attraction call when responding to their young, and a harsh, pulsed call when threatened by other females, males or alien pups. Elephant seals produce low-frequency sounds, both substrate-borne and air-borne. These sounds help maintain social hierarchy in crowded or noisy environments and reduce energy consumption when fasting.