Slumbering northern elephant seals on Año Nuevo.
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Photo by Brian Switek.
Slumbering northern elephant seals on Año Nuevo.

Science Word of the Day: Super-weaner

There are some technical terms that make me think “Hah, that’s funny”, but not actually laugh out loud. That’s how this weekly feature got started. But thanks to intellectual neoteny that has let me maintain a juvenile sense of humor, I can’t help but giggle at some science words. “Super-weaner” is one of them.

I first heard the word during a trip to California’s Año Nuevo State ParkAño Nuevo State Park. Scores of plump northern elephant seals haul out there every winter to breed, and since I arrived relatively early in the season, the stink emanating off the shore wasn’t too bad yet. A few mother elephant seals had even birthed their pups, which led the park ranger leading our tour to introduce us to “weaners” and “super-weaners”.

At first I thought the ranger was making a joke. It sounded like he was calling the pups “wieners”. Made sense to me. The pups looked like sausages wrapped in buns of blubber.

Of course, this wasn’t what the ranger meant. He was talking about how seals nurse. Weaners, not wieners. The higher echelon of my brain quickly scolded the baser part, and I learned the difference between the standard elephant seal pup and a super-weaner.

Mother elephant seals usually feed their pups for about twenty eight days. That might not seem like very long, but their milk is about 55% fat. That’s richer than heavy whipping cream, straight from the nipple. And given the thirst of their pups, mother elephant seals quickly become diminished. Already starting off depleted from a pre-birth fast, female elephant seals lose about half their body fat while nursing their offspring. After nearly a month of giving their pup everything, they need to return to the sea to feed. The 300 pound pup, now having to fend for itself, is a “weaner”.

But some pups still want more. There’s almost always another mother on the beach with a new baby, and some weaners badger and nag them to get more milk. Male pups are especially persistent, and, as Joanne Reiter and colleagues once wrote, “exceptionally large weaners are always males.”

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Get lost, weaner. Illustrations of female elephant seals rejecting a pushy pup. From Reiter et al., 1978.

It doesn’t always work. Most mothers don’t take kindly to alien weaners prodding them for milk. A swift bite sends most interlopers on their way, and the whole harem of females might join in if the weaner screams in protest. But, for reasons unknown to us, some mothers will let the intruding pups nurse. These pushy pups are super-weaners, and they certainly look the part. After supping on extra milk, super-weaners can weigh 600 pounds.

Not all super-weaners gain their edge through theft, though. There is a safer way for pups to become so bulbous. Some pups will be adopted by a second female while they’re still nursing or immediately after. They don’t have to try to “steal” milk, but can simply enjoy the largesse. Reiter and colleagues gave these super-weaners the extra title “double-mother sucklers”.

A few early season super-weaners inchwormed across the crowded beach during my December visit. They could still live large, at least for a little while. Little did they know that they would be cut off in March. At the cusp of spring all the mothers have typically vacated the beach, leaving the pups alone save for the beachmasters and adolescent males that spar in the shallows. So, with no one else to turn to, the pups do the logical thing to stay comfortable. They pile next to and on top of each other to bask in the sun. These, as you may have guessed, are weaner pods.


Costa, D., Le Boeug, J., Huntley, A., Ortiz, C. 1986. The energetics of lactation in the northern elephant seal, Mirounga angustirostrisThe energetics of lactation in the northern elephant seal, Mirounga angustirostris. Journal of the Zoological Society of London. 209: 21-33.

Reiter, J., Stinson, N., Le Boeuf, B. 1978. Northern elephant seal development: The transition from weaning to nutritional independence. Behavioral Ecology and Sociobiology. 3: 337-367.

Riedman, M., Le Boeuf, B. 1982. Mother-pup separation and adoption in northern elephant seals. Behavioral Ecology and Sociobiology. 11: 203-215.