Chinstrap penguins, known by their distinctive marking, are among the most prominent inhabitants of Antarctica. The black-and-white birds with their characteristic stripe at the throat breed at well-known visitor sites such as Half Moon Island and Deception Island. They also form the largest known penguin colony on Zavodovski Island, an island of the South Sandwich Archipelago, with around 1.5 million animals. A study by an international team has shown now that these seabirds may have experienced a marked decline over the past 30 years, especially along the Antarctic Peninsula.
The study by PhD student Noah Strycker of Stony Brook University in the USA concludes that there are currently about 3.42 million breeding pairs of chinstrap penguins in 375 colonies. But a comparison with numbers of colonies on the Antarctic Peninsula that have been under surveillance for some time shows that 45 percent of all of these colonies have seen a decline in the population and only 18 percent have seen an increase. However, the researchers also write that the numbers are difficult to compare with previous figures of the overall population. In addition to the usual on-site counting methods, the team also used the latest technologies such as high-resolution satellite images, fixed-installed cameras from the Penguinwatch project and aerial surveillance by unmanned aerial vehicles (drones). This was the first time that the researchers were able to produce a comprehensive study of chinstrap penguins and now publish the results in the journal Scientific Reports.
According to the researchers, most of the chinstrap penguins live in the South Sandwich Archipelago, where about 2.7 million animals are expected to exist. On the island of Zavodovski alone, there could be up to 1.5 million individuals. However, as the islands have been closely monitored only recently, comparisons with previous estimates are not possible. On the South Orkney Islands, the researchers estimate another 1.9 million animals in total and 0.5 million on Elephant Island. The smallest populations of the distinctive penguins are found on the remote islands of Bouvet in the Indian Ocean and Balleny in East Antarctica. A total of 375 out of 398 suspected colonies were confirmed by the researchers in their work, mainly thanks to satellite images.
As reasons for the decline of the chinstrap penguin colonies on the west side of the Antarctic Peninsula, the scientists suspect a connection with the reduced krill supply, which in turn has to do with the dwindling sea ice. Chinstrap penguins rely on krill as food, much like the related Adélie penguins. However, the researchers also suspect the increasing krill fishing as an additional pressure, as chinstraps tend to go foraging in the same areas as the krill fishing boats. In their study, the team tends to rule out a connection with rising whale and seal numbers as food competitors. Even a lower breeding success in the summer months does not explain the decline. Rather, according to the researchers, the focus should be on the overwintering period. Because here they suspect an important factor. But they hope to get more data in the future, especially from places such as the South Sandwich Islands or the South Orkneys. They see their work as a kind of baseline for future comparative studies to learn more about the populations of chinstrap penguins. This species could also be a red light for the ecological state of Antarctica and the effects of climate change in the white wilderness.
Dr Michael Wenger, PolarJournal
Link to the study: Strycker, N., Wethington, M., Borowicz, A. et al. A global population assessment of the Chinstrap penguin (Pygoscelis antarctica). Sci Rep 10, 19474 (2020). https://doi.org/10.1038/s41598-020-76479-3
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