Image of the Day: Penguin Populations
Image of the Day: Penguin Populations

Image of the Day: Penguin Populations

Chinstrap penguins are decreasing in numbers due to a lack of krill, their only food source.

Emily Makowski
Dec 3, 2019

ABOVE: Gentoo penguins (with red beaks, left) and chinstrap penguin (with white face, center)
RACHAEL HERMAN

Animals with specialized diets—such as chinstrap penguins, which only eat krill—could be more sensitive to the effects of human activities than those that eat a wider variety of foods, according to a study published yesterday (December 2) in PNAS.

Chinstrap penguins (Pygoscelis antarcticus) and gentoo penguins (P. papua) both live in the Antarctic Peninsula region of Antarctica, but the two species have different eating habits. While chinstraps exclusively eat krill, gentoos are generalists that can also eat fish and squid. Researchers led by Michael Polito of Louisiana State University analyzed amino acids in the penguin feathers of both species collected in the 1930s, 1960s, 1980s, and 2010s and found that while gentoos mainly ate krill in the 1930s, their diet has widened over the past several decades to include fish and squid. Meanwhile, chinstraps have continued to only eat krill.

The gentoos’ diet shift coincides with a decline in the Antarctic krill population starting in the 1970s due to warming waters and an increase in ocean acidification from climate change, along with the rise of commercial krill fishing for use in fish food and dietary supplements. While gentoo populations increased six-fold between 1979 and 2010, chinstrap populations in the region decreased 30–53 percent. This suggests that other penguin species heavily dependent on krill, such as Adélie penguins, could also decrease in numbers due to human-induced environmental changes, according to the authors.

Chinstrap penguins with egg
MICHAEL J. POLITO

K.W. McMahon et al., “Divergent trophic responses of sympatric penguin species to historic anthropogenic exploitation and recent climate change,” PNAS, doi:10.1073/pnas.1913093116, 2019.

Emily Makowski is an intern at The Scientist. Email her at emakowski@the-scientist.com