Each December, more than 3,000 northern elephant seals haul themselves out of the frigid Pacific waters onto the shores of northern California’s Año Nuevo State Park.

For the mothers among them, it’s a race against time. The 1,500-pound animals have just one month to give birth, nurse their pups, and wean them before returning to the ocean to eat and rebuild their strength.

It’s an extremely brutal lifestyle, with many females producing just a few pups before dying. But according to a new analysis of a half-century of data on more than 7,700 northern elephant seal mothers, just a small proportion of long-lived “supermoms” are responsible for most pups in the colony. Some of these moms raised 17 pups