Emperor penguins are the only animals that return to the Antarctic coastline in the winter time to breed and raise their chicks on the sea ice that is fastened to the continent. Because they live in such inaccessible places, emperor penguins have been traditionally difficult to study and that means that a full understanding of their habitat requirements and global population trends have been elusive until now. We combined counts of adult birds from aerial photographs and ground counts, with data from high-resolution satellite imagery (just like in Google Earth) to learn how many adult emperor penguins were in attendance at colonies in the springtime (mostly the months of September and October) during 2009-2018. We also wanted to understand what factors influence their choice in habitat: in other words, why do they live in some places and not in other places?

Accounting for observation errors and population processes in our statistical models, we learned that there is an 88% chance that the global population of emperor penguins in Antarctica is smaller in 2018 than in 2009 (going from approximately 250,000 birds to approximately 230,000 birds; these are indices of abundance). We estimate an approximate 9.6% decrease in the index of birds in attendance at the colony during the spring time, and we note that this is a conservative estimate since we are unlikely to be accounting for failed breeders or non-breeding animals. However, we cannot attribute the change we detected to any environmental variables yet, and changes in populations differed by region. For example, there was a decrease in the Weddell Sea sector but populations seemed to have remained stable in a few places like the Bellingshausen Sea. The declines we detected could be consistent with reduced breeding propensity, increased reproductive failure, and/or increased mortality of any age class, i.e. lower recruitment.

Emperor penguins are well-known to return to the same locations to breed and so we were also interested in the reasons emperor penguins choose certain locations to breed over others. We combined information about colony location with several characteristics about the fast ice (the sea ice "fastened" to land), and other physical and biological environment characteristics to determine if there is a set of criteria that emperor penguins "choose" when choosing their habitat to breed. As it turns out, the habitats emperor penguins choose are quite diverse and depend on the region where the colony is located. For example, in the Ross Sea (home to the largest marine protected area in the world since 2017) emperor penguins tend to choose habitat that is far from Weddell seals with low persistence of the fast ice; but in East Antarctica, emperor penguins like to be near Weddell seals and the persistence of the fast ice there is high. These two examples are basically opposites of each other. Within each region, we also found little difference between the colony locations and areas devoid of emperor penguin colonies. Together, we interpret this to mean that emperor penguins may exhibit what is called, "behavioral plasticity", which is another way of saying they can cope with unusual challenges.

In summary, we found a probable decrease in the index of abundance of birds we are seeing on the satellite images during the springtime over the course of 10 years. But, we note that emperor penguins seem to respond to their environments differently depending on the region, and there does not seem to be one defining factor that influences habitat selection for the species. Our work can be used to inform conservation and policy decisions within the Antarctic Treaty Consultative Meetings (ATCM), the Commission on the Conservation of Antarctic Marine Living Resources (CCAMLR), and the International Union on the Conservation of Nature (IUCN).

Last Modified: 10/29/2023
Modified by: Michelle A Larue