If you’re like me, some nights you stare up at your ceiling and think about life’s big questions. Where is the human race going? What would a Kanye-Coldplay album be like? What influences the distribution of breeding colonies of African penguin populations? Well, wonder no more about that last one. On today’s Research Thursday, we’re bringing you a paper titled “Influences of the abundance and distribution of prey on African penguins Spheniscus demersus off western South Africa.”
Full disclosure, Andrew and I are too cheap to pay the $50.00 required to purchase the entire article. We’ll then be taking a page out of Inception’s book by providing you a summary of the article’s abstract (which is a summary of the article itself). Dr. Rob Crawford and his team of researchers compared the distribution of African penguin breeding populations along the Western Cape Province with the populations of anchovies (Engraulis encrasicolus) and sardines (Sardinops sagax), two major prey items for the African penguin, in the same area.
What the discovered was that the temporal shift in these populations, meaning their changes over time, exhibited similar patterns of rises and falls. In 1996, for example, the combined spawner biomass and young-of-the-year biomass for sardines and anchovies measured in at < 1 million tons and 200,000 tons, respectively. The number of penguin breeding pairs during that year was 18,000. Over the next five years, the young-of-the-year biomass increased to 3.2 million tons and the number of breeding pairs rose above 30,000. If we go five years further down the road, young-of-the-year biomass falls to about 400,000 million tons and the number of breeding pairs drop to 21,000.
This evidence suggests that the population of African penguins is closely correlated with the biomass of some of its most popular prey items, in this case anchovies and sardines. While an all-you-can-eat anchovy and sardine buffet might make me personally want to puke, it may very well be one of the driving factors of successful breeding populations for these penguins. Changes in environmental or climatic conditions, or even fluctuations in prey items further down the food web could have caused the spike and subsequent drop in fish populations off the coast of South Africa. During times where food is scarce, African penguins may either not mate successfully or may not engage in mating behavior to conserve energy. However, once food is plentiful again, these birds get down to business. This type of data is crucial for endangered species like the African penguin. We can only prepare for and manage fluctuations in species distributions when we better understand what types of phenomena or conditions are associated with these changes.
It’s important to note, though, that correlation does not mean causation. It would be interesting to see if this study or other studies have been able to directly link prey availability in the area to African penguin breeding populations. While it certainly seems plausible that food availability is a critical component of favorable breeding habitats, I would bet that other variables like human activity, shelter, and atmospheric conditions may also influence fluctuations in the number of breeding pairs over the years.
Enjoy the Podcast!