A minority of 'super mothers' give birth to most puppies within an American elephant seal population in California. These 'super mothers' are an extreme minority among female marine elephants, but give birth to more than half of all puppies in the population. Scientists from the University of California describe the mothers in the scientific journal Canadian Journal of Zoology .
The scientists observed a marine elephant colony off the coast of Aña Nuevo, which lies below San Francisco. Here lives the northern elephant seal Mirounga angustirostris.
7,735 female marine elephants live in this colony. 6 percent of these females give birth to at least ten puppies in their lives. 55 percent of all young born in the colony come from these females. The scientists call these 6 percent 'super mothers'. The oldest 'super mother' in the population turned 23 and gave birth to seventeen puppies.
The 'super mothers' are mainly the older females, which is remarkable according to the researchers. "You would expect the many young females to contribute more to the population." This probably does not happen because many female northern elephant seals die young before they can mate. The females that do mature are usually only one to three times pregnant.
For a young female, giving birth is hard, because they have to spend a lot of time raising their young, while they also develop themselves. The 'super mothers' apparently can do this.
Sea elephants give birth to one puppy every year in the winter and usually starts with that when she is three or four years old. One of the 'super mothers' gave birth to a puppy sixteen years in a row.
Most puppies do not survive the first visit to the sea
After birth, the young are breastfed for four weeks. After those weeks the pup learns to hunt and goes into the sea to look for food. Many puppies do not survive their first visits to the sea, possibly because they cannot find food or because a predator finds the pup.
The scientists are not sure why the mortality rates among puppies are so high, because the animals often die in the sea and it is therefore difficult to observe.
It was, however, relatively easy for these researchers to observe the marine elephant colony for fifty years. The coast where the colony lives is pretty close to the campus of the University of California in Santa Cruz.
The sea elephant colony on the beach at Año Nuevo. (Photo: Wikimedia Commons / Rhododendrites)