Monday, February 15, 2010

Foster Mothers

At the north end of the beach, where last year there would have been hundreds of pups and weaners, there are about four dozen. A lot of sand is washed away.

The survivors crowd together in the space available, and more are moving higher on the banks. One even moved almost to the trail. Visitors stand about six feet from this large weaner.

My impression is that many of the surviving pups are much larger than usual. This one is very large. Sampling weights would be a good research project this year. Because so many pups were washed away, a lot of mothers were left with no pup to nurse. Biologists suspect that the females have to lose some amount of weight in order to trigger estrus and mate. Many stayed on the beach and nursed any willing pups.

Pups are born weighing 65-80 lbs. They can gain as much as 10 lbs. a day, nursing on the high-fat seal milk. By the time lactation is concluding, they weigh 350-400 lbs. Some are fully nourished by their own mothers, then go on to steal milk from other mothers. They get even larger, well over 500 lbs. Looking over the beach, I saw plenty of weaners with rolls of fat circling their chubby necks. One lost his balance and rolled down the beach, so fat he was unable to stop himself.
This mother is nursing two pups at the same time. Some mothers are willing to nurse all comers, others are more limited in their tolerance. Researchers have found that females who nurse additional pups gain experience as mothers. A female can carry only enough weight to nurse a single pup, and twins have never been observed, so are probably never born. But the practice of sharing milk is certainly commonplace, at least this year, when harsh weather has caused so much chaos on the beach.

No comments:

Post a Comment