AUDIE CORNISH, HOST:
Hundreds of thousands of penguins make their home on a patch of seashore along the coast of Argentina. It's called Punta Tombo. Science correspondent Christopher Joyce went there in 2003 for NPR's Radio Expeditions program. He visited a biologist who's been studying the penguins who now says our changing climate is threatening the colony.
CHRISTOPHER JOYCE, BYLINE: When I visited Dee Boersma in 2003, she was living in the midst of the world's largest colony of magellanic penguins. And she was worried. Their numbers were dropping by 20 percent that year. You wouldn't have known it, though, on the beach at Punta Tombo. Once you walked over a big dune, it was all penguins.
(SOUNDBITE OF PENGUINS)
JOYCE: A stunning army of fluffy, two-foot-tall birds. They're also called jackass penguins, for obvious reasons.
(SOUNDBITE OF PENGUINS)
JOYCE: Nearby was a ragged, double-wide trailer, at the time, Boersma's temporary home away from the University of Washington.
DEE BOERSMA: We get to live really close to the penguins. See right here, right underneath the trailer?
JOYCE: Oh, there's, there's a penguin right under the trailer.
BOERSMA: That's right. And, in fact, last night, there were fights under the trailers.
JOYCE: That was Boersma's 20th year at Punta Tombo.
BOERSMA: One of the things that I certainly didn't anticipate when I started this is that these penguins could tell us as much as I think they are starting to tell us about the environment.
JOYCE: What they were saying was things weren't going well. The colony had shrunk and Boersma didn't know why. She had electronic tags on some penguins, and she knew they were swimming farther than normal to find food. She suspected that something in the environment was changing.
BOERSMA: It could well have something to do with the long-term climate changes or the variation in climate changes.
JOYCE: It wasn't until around 2010 that Boersma figured it out: bigger, stronger, wetter rainstorms.
BOERSMA: When you get three years in a row where lots of chicks die because they get wet, it hits you pretty hard.
JOYCE: Now, wait a minute. Penguins swim. They live in cold places. And they were dying from hypothermia after a heavy rain? How can that be?
BOERSMA: Chicks are covered in down and they don't get their juvenile plumage. It doesn't even really, you know, come in to protect them at all until they're older than 40 days. So until they get some of their juvenile plumage, they're not waterproof at all.
JOYCE: And local weather records showed that things had been changing for years.
BOERSMA: There's more rainfall and more of these severe storms. And that's what can kill penguin chicks, if the storm comes when they're vulnerable.
JOYCE: And they are more vulnerable. Here's why. Usually, the penguins hatch their young at the same time - over about two weeks in December. But now, for some reason, they're hatching over a six-week period. So the period of time when chicks are vulnerable to storms has increased. Moreover, the hatch is now later in the year, when there are more storms. The penguins are struggling with this new climate. In one year, half the chicks born died in storms. On a few occasions, chicks have also died from heat waves.
BOERSMA: It's these climate change events that penguins didn't have in the past, and it's not like penguins can adapt.
JOYCE: Boersma published her findings in the journal PLOS One. She got research funding from the Wildlife Conservation Society. The society's South American expert, Martin Mendez, says when things go wrong with wildlife, it's hard to track down the cause. There are so many potential culprits.
MARTIN MENDEZ: This show you the value of being on the ground for a long time, especially as it relates to climate change.
JOYCE: Boersma has 30 years of data on her colony. Mendez says one other project in the region has that kind of history - in the Patagonian Mountains. There, there's less rainfall on average now. And that's changing the mountain lakes, where Argentina's flamingos live.
MENDEZ: And the less water, they become more salty and more suitable for flamingos.
JOYCE: For wildlife, a changing climate is a crap shoot. Christopher Joyce, NPR News.
CORNISH: And those penguin recordings you heard came from the Radio Expeditions archive at the Cornell Lab of Ornithology.