A single male elephant seal can guard a group of up to 100 females during the breeding season.

Northern Elephant Seals gather on beaches like Año Nuevo State Park in California from December to March. A dominant male is called an alpha bull. He can weigh 2,300 kilograms or 5,000 pounds. This is about three times heavier than a female seal.The alpha bull uses his size to keep other males away from his group. Researchers from the University of California, Santa Cruz, found that alpha males do 90% of the mating in their group. Other males stay on the edges of the group and wait for a chance to challenge the leader.Defending a harem is hard work. The alpha bull does not eat or drink for up to three months so he never has to leave his spot. He survives by burning the thick layer of fat, or blubber, on his body.Female seals arrive at these beaches to give birth to pups born from the previous year. A few weeks after giving birth, they are ready to mate again. This timing keeps the whole colony together while the large males provide protection.