The Smell Test

The reasons a man has for holding poop and feathers under the beaks of sleeping penguins.

October 21, 2015

Photo: Gregory Cunningham

When winter struck last year, Greg Cunningham went south to hit the beach for a month. Scratch any mental images of sipping mai tais and surfing—it wasn’t that kind of beach. Cunningham, a biologist at St. John Fisher College in Rochester, New York, was holed up in a hut in Antarctica. His companions were a few humans and 200,000 king penguins that breed on a flat stretch of Cape Ratmanoff, on Kerguelen Island.

“You hike seven hours from the main base to get to the beach, come around a corner, and are greeted by the sight of all these penguins,” says Cunningham. “I’d seen it before on a previous visit and knew what to expect. But still. You stop and make some rather flowery comments about how incredible it is—you can’t help yourself.”

Photo: Gregory Cunningham

Incredible they are, and so is the stench their mass congregation generates. But the odoriferous environs were rather fitting, given what Cunningham was there to investigate: a penguin’s sense of smell. He did this by sneaking up to sleeping birds and placing feces beneath their beaks—obviously.  

“I’m out there on a beach doing something a six-year-old might have thought up,” he says.

The approach might be simple, but the study is shedding light on an area that’s been virtually untested. Even though kings, second only in size to emperors, nest in dense colonies and are among the best-studied penguins in the world, nobody had ever examined the bird’s olfactory prowess. Cunningham says that’s probably because of the long-held—and incorrect—belief that most avian species can’t sniff out scents. “When I was an undergraduate, I remember my ornithology professor saying, ‘Birds don’t have a sense of smell, let’s move on.’” The prof was way wrong, but that widespread misconception meant that the field of avian olfaction was wide open for study—and Cunningham jumped right in.

Photo: Gregory Cunningham

Most of the olfaction work on marine birds has focused on how they find food. Trying to pinpoint schools of fish or krill from above or within a vast, dark ocean is a daunting task. Cunningham’s mentor, biologist Gabrielle Nevitt, has proposed that petrels and other tube-nosed procellariiformes (an order of seabirds) actually home in on prey by detecting a chemical they emit called dimethyl sulfide, or DMS. What looks like a flat ocean to human eyes is, actually, to a bird’s sniffer, a dramatically varied landscape with peaks of DMS above areas with high concentrations of food.

Cunningham previously studied how blue petrel chicks learned to detect odors while still in the burrow and showed that African penguins can smell DMS. For his latest work on king penguins, he teamed up with Francesco Bonadonna, of France’s Center of Functional and Evolutionary Ecology, to explore the gastronomic and social roles scents may play. The research could help explain how penguins find their way back to remote breeding grounds and locate their offspring among the masses, and possibly enable scientists to better predict how the birds will fare as sea temperatures continue to rise and food becomes less available.  

Originally, Cunningham had planned to test whether chicks can smell. When birds are a few days old, it’s easy to lull them to sleep by holding an incandescent light bulb nearby. “As a biologist, I should never say this, but it’s super cute,” he says of the technique, which he previously applied to blue petrels. Once they nod off, you present them with different scents and see how, or if, they respond. Unfortunately, the young penguins at Cape Ratmanoff were too mature for this trick. “The chicks were huge, and they go crazy if you pick them up,” Cunningham recalls.

So instead, the team tried putting odors on the stretches of ground where the birds walk a lot, but that didn’t work either. “The winds down there are quite fierce… mak[ing] working with odors hard,” he says. Then Cunningham went high-tech, sending out a remote-control car attached with a GoPro camera and a petri dish of smelly cotton balls. Alas, the rig couldn’t handle the terrain.

At that point, 10 days into his 30-day trip, Cunningham grew frustrated. He was sitting in the kitchen (where by the way, his French colleagues baked fresh bread every day, even croissants once), staring out the open doorway at penguins and wishing he’d arrived early enough for the light-bulb trick. That’s when he realized he was looking right at about 30 birds sleeping naturally.

Cunningham spent the next couple of weeks sneaking up on as many dozing penguins as he could find. In all, he tested 108 adult kings. For each trial, he’d take a stick, attach duct tape, and roll it in a sample—sand, feathers, or feces. The sand and feathers were abundant and easy to collect; the guano took more effort. “You’d be amazed—on a beach with 100,000 penguins, sometimes it would take forever to get a sample,” he says. “I’d think, ‘Guys, I’ve been waiting here for 15 minutes. Someone please poop.’”

By and large, the birds didn’t react to sand, but the feathers and poop elicited a strong and similar response. “They woke up quite commonly and would give you a honk,” says Cunningham, who published his results in the Journal of Experimental Biology. His team proved that king penguins can smell, but “we haven’t really cracked the code as to what it means,” says Cunningham.

They have a few ideas.  The birds may sniff their way back to the colony from feeding grounds, which can be 250 miles away. A sense of smell might also help the birds find their offspring and partner once they return. Previous research has found that the penguins go to a “rendezvous zone” within eight meters of their chick or partner and then start to sing for recognition. “But we don’t know how they get to that rendezvous spot,” says Cunningham. “It could be that they use smell to find the colony, then switch over to acoustic cues when they get to the neighborhood where their family lives.” (Chicks stick close to where they hatch, so the same birds are in close association with each other, which may give groups a distinct odor profile.) Finally, penguins might use scent to identify individual birds.

The findings are only the tip of the iceberg of understanding king penguin olfaction, says Cunningham, who’s back in Rochester these days. He might be home, but Antarctica continues to invade his slumber. “The very few reoccurring dreams I have are of that place,” he says. Maybe someone is holding something under his nose. 

Photo: Gregory Cunningham

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