When the keepers at the Netherlands' Emmen Zoo opened the night enclosure for 112 baboons on July 29, they expected the animals would be, as usual, eager to get inside.
After all, the baboons knew there was food for them in there.
Instead, biologist and zoo press officer Wijbren Landman tells All Things Considered the baboons didn't want to budge. "It took us about an hour to get them inside," he says. That night, the baboons didn't eat.
Over the next week, the baboons continued to behave oddly. They would sit with their backs to the public. They wouldn't make much noise; "it was rather silent, which is not normal for a baboon," says Landman. They were, in a word, looking rather sad. The zoo took to calling them "troubled."
It was about a week before the baboons began acting like themselves again.
So what happened?
It's a mystery, Landman says.
Just as when this sort of thing occurred at the zoo three times before — in 1994, 1997 and 2007 — keepers don't have any clear idea about what caused such melancholy. The most likely explanation seems to be that something was bothering one of the male leaders and others behaved as he did.
"If one of the leaders is shocked by something than most of the colony will obey him and then the whole colony will be shocked," says Landman. "But what really caused one of the leaders to be shocked, well, we didn't find out."
Among the theories:
-- Lightning and thunder during storms that came through the area.
-- An earthquake that escaped the attention of humans (though we don't see any near the Netherlands on the U.S. Geological Survey's record of temblors for July 31).
-- A snake or some other kind of animal entering the baboons' area.
-- Aliens. "We didn't see them. Maybe the baboons saw them," Landman says with a laugh.
As you might imagine, there's also no clear answer for why the baboons have seemed to cheer up.
Theories are welcomed in the comments thread.
For much more on baboons, including audio of their sounds, check this package by National Geographic.
We'll add the as-broadcast version of Landman's conversation with NPR's Melissa Block to the top of this post later. Click here to find an NPR member station that broadcasts or streams the show.
MELISSA BLOCK, HOST:
To the Netherlands now where something has traumatized a large group of baboons at a zoo. Last week, the normally gregarious troupe of 112 baboons at the Emmen Zoo suddenly stopped eating. They sat motionless and turned their backs on zoo visitors.
Wijbren Landman is a biologist and a spokesman at the Emmen Zoo. He said the first sign that something was wrong came at night when the baboons are supposed to head indoors.
WIJBREN LANDMAN: In our zoo, all the animals are in night enclosures, and the baboons would normally go to that night and closure without any problem. And we open the door, and within 30 seconds, 112 balloons are inside. But that evening, it took us about one hour to get them inside. So there was certainly something strange going on.
BLOCK: And were they vocalizing in any way?
LANDMAN: No. It was rather silent, which is not normal for a baboon. They - it is a very social group, and they are constantly communicating with each other. And, well, they didn't.
BLOCK: And at some point, as we say, they turned their backs on zoo visitors, which I would say might be a completely understandable behavior, but I guess would be a little unusual, right?
LANDMAN: Yes. That is not what they normally do. Normally, let's say, a baboon mother carrying a just-born baby has her back between the baby and the visitors. But they did it all, and that is not normal.
BLOCK: Well, are there any explanations for what caused this trauma or this panic among the baboons?
LANDMAN: Well, we had almost 300 explanations of all different kinds.
BLOCK: What were some of those ideas that you did field?
LANDMAN: Well, we had some suggestions about real bad weather we had on Sunday with extremely many lightnings and thunders. Some suggestions were earthquakes, escaped snakes, big predators. Well, we are near in the city center, so there are no big predators coming here. We even had the reason that there were aliens or unidentified flying objects coming on so - but we didn't see them, so maybe the baboons saw them.
BLOCK: Mm. So nothing that makes sense.
LANDMAN: No. No.
BLOCK: Well, this has happened before, is that right...
BLOCK: ...among the baboon population at the zoo, that they've shown this behavior before.
LANDMAN: Yes, they did this in 1994, in '97, and in 2007.
BLOCK: Well, Mr. Landman, how are the baboons doing now? Are they back to normal?
LANDMAN: Yes. The whole strange behavior took about a week. And at this moment, we don't see any strange behavior anymore. Now, they are strolling around in harem groups, which is normal by baboons. A male with, you know, depending on his social position, he has two to six females around him, and they are grooming each other within a harem. Males fight for their social position. Young baboons are punished for being disobedient. They mate, which is a very important behavior in baboons. So they are back to normal.
BLOCK: Oh, so the mystery remains.
LANDMAN: It's still a mystery, yes.
BLOCK: Well, Mr. Landman, thanks for talking to us about it. And glad to hear the baboons are - seem to be happier now.
LANDMAN: Thank you.
BLOCK: That's Wijbren Landman. He's a biologist and spokesman at the Emmen Zoo in the Netherlands. What's the word for baboon in Dutch, by the way?
BLOCK: Baviaan? Baviaan?
LANDMAN: Yeah, baviaan.
BLOCK: Baviaan. I learned a bit of Dutch today.
LANDMAN: It's a good word to know in the (unintelligible). Transcript provided by NPR, Copyright NPR.