The annual breeding cycle of the northern elephant seal begins in December, when the huge males haul out onto deserted beaches. Large numbers of pregnant females soon follow the males, aggregating into large groups known as harems, with each group presided over by a large, dominant male (3). Competition for this dominant position is intense (3), with males establishing their supremacy through stares, gestures, and snorts and grunts amplified by the inflation of their proboscis (2). Spectacular fights may ensue, with males delivering serious, but rarely fatal, blows with their large canine teeth (2).
Between two and five days after arriving at the colony, each female will give birth to a single pup (3). For the next 27 days (2), the female will stay with her new pup, feeding it large quantities of rich, fatty milk, while she relies on her own thick blubber for sustenance (3). Shortly before the young are weaned, the females come into oestrus and mate with the dominant male. After weaning their young, the females return to sea, leaving the pups to fend for themselves (3). For the next four to six weeks, the pups practice swimming and diving, before leaving the beach where they were born to spend the next six months at sea. Northern elephant seal pups are highly vulnerable at this time, with around 30 percent perishing (3).
After breeding, many northern elephant seals travel north towards Alaska to feed. Northern elephant seals feed primarily on deepwater fish and squid, a diet that necessitates an exceptional diving ability (3). They can dive down to over 1,500 metres, remaining underwater for up to an extraordinary 120 minutes, although most dives are to shallower depths and last for around 20 minutes (3). More than 80 percent of the year is spent feeding at sea, in order to build up their essential blubber stores to provide energy for breeding and moulting, times at which the seals do not feed (3).
Northern elephant seals return to their southern breeding ground to moult, a process in which the very outer layer of skin is shed in addition to the hair. As rich supplies of blood are pumped to the skin to enable the growth of the new skin and hair, conserving body heat becomes essential, and so the seals do not enter the water to feed for the next three to five weeks (3). Following moulting, northern elephant seals travel northwards once more, before returning to their breeding colonies to commence the breeding cycle again. This remarkable journey, undertake twice each year, covers an impressive 10,000 kilometres (3).