Los Farallones

Dispatches from Point Blue’s field station on the Farallon Islands National Wildlife Refuge

Oh the Times They Are a Changin’

By | February 10, 2018

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Early February is a time of change for the Southeast Farallon Island’s northern elephant seal inhabitants. Since our last update, we have had some amazing weather and that has allowed the young seals that survived January’s storm to continue to nurse and grow. In fact, earlier this week we had our first pups successfully wean from their mothers! These individuals have put on some considerable weight during the nursing period, a phase that takes an average of 26.5 days! (Costa et al. 1986)

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The next few weeks will be an interesting time for these weaned seals as they prepare to head off into the harsh north Pacific in search of food. The first thing that will happen to these young animals is that they will molt their black lanugo fur for a fresh, shiny, silver coat (stay tuned for photos of shiny new coats in the weeks to come!).  This molting will occur quickly over the next few weeks as the weaned pups spend their time learning how to move and swim like a seal. The young seals are able to do all of this without continuous nursing because of the large energy transfer that takes place from mother to pup during the nursing period.

Speaking of mother seals, early February is also a very important time for the population of adult female seals on the island.  After fighting storms, hot weather, angry bulls and each other, the female elephant seals are beginning to depart the island and their pups for their short pre-molt, foraging migration. The winter is a trying time for adult female seals, and this year’s season has taken a lot out of our local cow population, quite literally.

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Female elephant seals lose an average 42% of their total body mass during the nursing period (Costa et al. 1986). Around the time that the cows finish nursing their pups, they will go into estrous so that they can mate with an adult male seal prior to departing. They will not return to the island until next winter, when they are ready to give birth to a new generation of seals.

Early February is an important time for the large male elephant seals of the island as well. While the male seals have been fighting for dominance all season, we have seen a notable uptick in male versus male confrontation. The non-alpha males are attempting to mate at any opportunity that arises, and our resident alpha male (who we have affectionately named Becky) is being forced to move all around the colony to defend his harem. With all the testosterone in the air, we have been fortunate to observe a couple male seal interactions, which we have recorded so that we can share them with you here on the Los Farallones blog.

 

Work cited

Costa, D. P., Boeuf, B. J. L., Huntley, A. C. and Ortiz, C. L. (1986), The energetics of lactation in the Northern elephant seal, Mirounga angustirostris. Journal of Zoology, 209: 21–33. doi:10.1111/j.1469-

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