Donna Fraser remembers the day in 1993 when her team found the first gentoo penguin nests ever recorded at Biscoe Point. Fourteen pairs had set up a tiny colony on the rocky headland, which lies just 8 miles from Palmer Station. Gentoos are Fraser’s favorite penguin, and her response was, “Awesome, we’ve got gentoos in our study area!” But as much as she likes them personally—“I think gentoos just make everything right with the world,” she told me—it’s been a shock to see how drastically Adelie penguins have declined while gentoos have increased in the last 20 years.

Fraser and other penguin scientists are still researching the details of this switch, but the root cause is clear. The climate around Palmer Station has become more suitable for gentoos and less suitable for Adelies—and in geological terms it’s happened quickly. Click through the slideshow to explore the gentoo arrival in more detail:

My descriptions of penguin sounds weren’t so good, but fortunately I also have recordings from a couple of the nearby colonies. Listen to them below—and then if you can think of a good way to describe the sounds, write it in the comments. We’d love to hear your descriptions.

Here’s the gentle sound of a gentoo penguin colony from Biscoe Point, recorded on Jan. 12:

And here’s the harsher sound of an Adelie penguin colony from Torgersen Island, recorded on Jan. 10:

***Mt. Shackleton was named for the great British explorer Ernest Shackleton, who nearly reached the South Pole in 1908 and who sailed into the Weddell Sea in 1914 on a ship called the Endurance. The penguin team’s Shawn Farry reminded us that today was the 100th anniversary of the day that the Endurance became trapped in sea ice, forcing Shackleton and his men to camp out on the sea ice for the winter—and that’s just the beginning of one of the greatest survival stories in Antarctic history.