Mirounga Mania!

Northern elephant seal rookery. Photograph by Sarah Chinn

This is one of the most spectacular times of the year and one of my favorites because the Northern elephant seal (Mirounga angustirostris) breeding season is underway. Thousands of elephant seals emerge from the ocean to fill selected beaches along the west coast of the US. These areas are called rookeries. Within the rookery there can be several alpha bull males who defend a territory that includes several females, his harem. Males can grow up to 16 ft and weigh between 3,300-5,000 lb, while females are smaller and can grow up to 11 ft and weigh between 990-2,000 lb.

Adult male elephant seals fighting. Photograph by Sarah Chinn.

During the month of December males arrive to challenge and battle other males over beach territory. When a battle ensues it can either fizzle rather quickly with the dominant male simply vocalizing his adversaries back into the water, or forever brand your mind with a ferocious, full-contact spectacle. Elephant seals get their name from their unique proboscis. Mature bulls males develop the pronounced trunk nose by about 9 years-old. Also, in order to be considered a bull versus a sub-adult male, he must develop a full chest shield – like a callus around his neck to use to hit another male and also protect him against the blows during a fight.

Females arrive a few of weeks after the males have battled over their tenuous territories. Elephant seal females are gregarious and will congregate together to give birth, nurse their pups, and copulate. During the entire breeding season, alpha males are constantly defending their territory borders and females. However, females are free to move throughout the rookery from harem to harem.

Female elephant seal with pup. Photograph by Sarah Chinn.

At birth elephant seal pups are about 4 ft long and weigh 75 lbs. Pups are born with a dark black lanugo coat. They are nursed by a female (not necessarily its mom) for about 28 days before she abruptly weans the pup, all without teaching it how to swim or catch its own food. After 4 weeks of nursing her pup without eating anything herself, a female may have lost about one-third, or about 500 lbs, of her own body weight.

http://www.youtube.com/watch?v=kwKcI5lIfIk&feature=youtu.be

The “weaners’” then molt, with their fur coat turning light silver and then gradually to gray or brown over the next year. Often times as the emaciated female is leaving the beach for the ocean, she is copulated with by the alpha male of the harem. A successful alpha male can copulate with more than 50 females during the breeding season.

As March approaches, the rookery demographics change. Most of the females have gone back into the ocean to fatten up for next year’s pupping season, leaving their weaners and the adult males on the beach.

For a live streaming view of a rookery, please visit Friends of the Elephant Seal live webcam in San Simeon, CA http://www.elephantseal.org/Rookery/livecam.html. I highly suggest that everyone experience this event in person if at all possible, it is an amazing sight to witness the life history of the largest pinniped.