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February 23, 2006

Northern Elephant Seals: Pups

A Very Pregnant Female Elephant Seal
Año Nuevo State Reserve

When a female Elephant Seal hauls out at Año Nuevo State Reserve in late December or early January, it certainly isn't easy. She's been at sea for many months and now she's very, very pregnant. And now, as she hauls her big body up onto the sand dunes, she has to run a gauntlet of eager males wanting to mate prematurely, and find a safe harem to birth her helpless little pup. She generally gives birth that first week, usually within five days of coming ashore.

Births Are Followed By Shorebirds Eating Afterbirth
Año Nuevo State Reserve

Not many people ever witness an Elephant Seal birth. The cow only ever gives birth to only one dark brown-furred pup, which weighs between 60 and 90 pounds. The pup is born with his eyes open and can move soon after, snuggling at his mother to nurse. You can often tell where a birth has happened because lots of gulls will land nearby to eat the afterbirth.

Cow & Pup Bond Vocally
Año Nuevo State Reserve

Soon after a cow gives birth, she will vocalize, or sing, to her new pup. The pup responds by yapping a bit and now the cow will be able to recognize her own pup amongst the others, should they be separated. That said, the cow will not leave her pup willingly for the entire time she nurses him - 28 days. However some pups wander off, or are separated when an alpha bull flops by. The male plays no role in the raises of young.

Cow & Pup Bond For The Month
Año Nuevo State Reserve

The cow and pup will spend the first 28 days together. During this time, the cow will have no food or water. She will devote herself exclusively to nursing her newborn. It is very important that the pup gets to nurse for the full four weeks, for he was born without the protective blubber to keep him warm, nor does he know how to swim. He will need that milk.

Pups Drink Rich Fatty Milk
Año Nuevo State Reserve

Although the pup is very small when he is born, he grows fast, sometimes gaining 10 pounds a day. Within a week, he has doubled his birth weight. The thick, oily milk he nurses is 55% butterfat, full of fat and protein. Soon he will be so fat that although he hasn't learned to swim, he cannot sink, either. By the end of the month, the cow may have dropped almost 50% of her body weight.

Cows Bicker Over Harem Spots
Año Nuevo State Reserve

The cows of the harem bicker and nip at each other over the best spots in the harem, but they don't fight like the males do. She feeds her pup until he looks like a fat little sausage, having grown not much in length but decidedly in girth. She does not teach him anything, though. If she has not chosen a safe spot to nurse him, storm surge and flooding can drown the little pups before they are old enough to fend for themselves.

28 Days Later, Weaned Pups Rival Mom
Año Nuevo State Reserve

After a month of nursing, the cow goes into estrus, or heat. She mates with the male during these last few days as she weans her pup. Then, she returns to the sea. By the time she weans her pup, he is almost as big as she is. These newly weaned pups are left to fend for themselves, and they produce a mighty racket in protest. They are now called weaners.

Milk Thieves Become Super Weaners
Año Nuevo State Reserve

Some weaners don't much like being weaned. They become milk thieves, stealing milk from another cow and depriving her pup. Some weaners manage to nurse for ANOTHER 28 days, and become so fat, they are called super weaners. These guys can weigh up to 500lbs and are generally males. Funny that.

Pup Mortality Is High
Año Nuevo State Reserve

Despite the fact that Elephant Seals have no real predators on land, pup mortality is still about 50%. Some pups are trampled to death by passing males; others wander off and lose their mothers. Coyotes help keep the beaches clean. Still more will be eaten once they enter the water, which is full of great white sharks, the primary predator of the Northern Elephant Seal. In fact, the great whites of the San Francisco Bay area are significantly larger than the ones around South Africa for this very reason - diet. Our great whites eat big, fat Elephant Seals, while the South African great whites feast on the much smaller Cape Fur Seal.


Posted by sorsha at February 23, 2006 1:41 PM

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hi i just been to Ano Nuevo today for a class fieldtrip


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