ABOVE: Adélie penguin family Jacqueline Deely

Penguins are some of the slowest-evolving birds ever studied, a trait that could make them particularly vulnerable to the effects of climate change, according to a paper published today (July 19) in Nature Communications

Researchers used genomic and fossil data to piece together the history of penguin diversification starting 60 million years ago, when the birds lost their ability to fly. The team found that although penguins have become highly specialized to thrive in their extreme environments, their evolutionary rate has decreased drastically, meaning that they may struggle to adapt to rapidly warming ocean temperatures and other effects of anthropogenic climate change.

“Modern penguins seem to be less well equipped to survive these rapid environmental changes than ancient penguins because of this decrease in evolutionary rate,” Vanesa De Pietri, an avian paleontologist at the United Kingdom’s University of Canterbury who was not involved in the work, tells National Geographic“Have they specialized themselves into a corner? Yeah, probably.”

The study identified various ways in which penguins’ evolution has tracked geological and climatic conditions in the past. For example, many of the 18 species of penguin in the world today seem to have arisen within the last 3 million years—something that the researchers suggest was driven by climatic changes leading up to and following the last ice age. 

“As ice volumes increased during the [last glacial period,] high-latitude penguin species were likely forced into isolated mid-latitude refugia,” the authors write in their paper. “As climate warmed from the late Pleistocene to Holocene, these species moved back towards the poles, recolonizing landmasses and islands as they became habitable once again, and, notably, experiencing secondary contact with one another.”

It’s not clear exactly what caused penguin evolution to decelerate to the extent that it did. While the birds’ large size and slow reproduction may play some role, “we would never have guessed that would have the slowest rate yet seen in birds,” study coauthor Daniel Ksepka of the Bruce Museum in Greenwich, Connecticut, tells the UK Natural History Museum (NHM) news site.

The researchers note that penguins’ sister group, the Procellariiformes—which includes albatrosses and other seabirds—also have low evolutionary rates compared with those of other avian orders, suggesting there might be “a gradual slowdown associated with increasingly aquatic ecology,” they write in their paper. 

“It’s a topic that certainly warrants more investigation to try and discover why this occurs,” Ksepka tells NHM.