It should have been obvious as the beaks on their face that penguins have an acute sense of smell, but scientists at Brookfield Zoo and University of Chicago discovered that there was scant research showing how penguins used smell to get along.
In a study released in September, two local scientists who live in Brookfield and Riverside have managed to prove that Humboldt penguins can recognize neighbors and relatives by the smell of preening oil on their feathers.
"These birds live in giant groups in Punto San Juan, Peru, where everybody looks pretty much the same," says Jason Watters, Brookfield resident and director of animal behavior research at Chicago Zoological Society. "It's important for birds to know who their neighbors are so that they can find their nesting areas."
And, since siblings from previous years return to nesting areas, it's important for birds to avoid the potential of becoming mates. Humboldt penguins recognize their own relatives by smell, even if they've never met before, the study shows.
Scientists have long known that birds - especially sea birds - have a large "olfactory bulb" that sends nerve signals to the brain. Sea birds use odors to navigate and sniff out chemical odors given off by food. But birds also have good hearing and often excellent eyesight.
"It's hard to tell if a bird is sniffing something" said Riverside's Jill Mateo, a kin recognition expert at University of Chicago's Department of Comparative Human Development. She and Watters both advise the Committee on Evolutionary Biology at University of Chicago.
Their research helped complete an article titled "Odor-based Recognition of Familiar and Related Conspecifics: A First Test Conducted on Captive Humboldt Penguins (Spheniscus humboldti)" in the scientific journal PLoS ONE.
The study's lead author was University of Chicago graduate student Heather Coffin. Research was conducted in 2009. The zoo has two groups of penguins - some on display and some not - and keeps detailed animal husbandry lists of who's related to whom. Other zoos also have Humboldt penguins which they swap around - also with long pedigree lists. The study tested around 20 birds.
Scientists swabbed preen oil from a gland near the penguins' tails and then wiped it inside dog kennels that resemble the nests where the captive penguins live at the zoo. Preen oil helps penguins keep their feathers from becoming waterlogged and disintegrated by sea salt.
For the first experiment, one cage was swabbed with oil from a familiar bird who was no relation, and the other from an unfamiliar, non-kin bird.
"We shut the door and spied on them," says Watters.
Penguins waddled into cages that smelled like neighbors they knew and avoided "going into a stranger's nest," Watters said.
For the second experiment, cages were swabbed with oil from kin who were strangers to the penguins and unfamiliar birds who were no relation. The penguins favored the cages that smelled like oil of non-relatives.
"This is the first study to provide evidence for odor-based kin-discrimination in birds," said Mateo.
Humboldt penguins are an endangered species living in South America. They are monogamous, live for 20 years and return to the same nesting site every year. They share Brookfield Zoo's Living Coast exhibit with Inca terns and grey gulls.
Mateo says other animals such as montjac deer and ground squirrels, which live in colonies, recognize kin via sense of smell. This is an evolutionary behavior to avoid mating with a relative, she says.
"There's some evidence that even humans do," she says.
Much of intra-human odor recognition is unconscious.
"When you grow up you form a template [of smells] and when you encounter strangers, there's a degree of match related to the strangers."
"Even though we try to mask and alter our odors," adds Watters.
The Living Coast exhibit has a definite odor, visitors note.
"That's more of an oceanic smell and the smell of their food," says Mateo.
But she says she herself didn't notice a specific smell of the penguins.
"I couldn't smell the preen oil on the swabs at all," she says.
The research may be helpful when relocating birds to the wild, by allowing naturalists to apply familiar-smelling preen oil to a release area so birds feel at home.
Mateo hopes the research will shed light on more bird behavior based on sense of smell.
"Song birds often display a behavior called bill wiping [where they wipe their beaks on sticks or tree trunks]. It has no known function," says Mateo. "Maybe it has something to do with [the smell of] preen oil."