Penguins may be able to smell some feathery, waddling whiff of kinship on others of their kind.
In some sniff tests, Humboldt penguins (Spheniscus humboldti) in the Brookfield Zoo outside Chicago could discriminate between the odor of birds they knew and birds they weren’t familiar with, says Jill Mateo of the University of Chicago. More intriguingly, the birds also showed evidence of an ability to distinguish between the scents of relatives and nonrelatives even if they weren’t personally familiar with the scent owners, Mateo and her colleagues report September 21 in PLoS ONE.
The ability to recognize kin by smell has shown up in many other kinds of animals, including mammals, amphibians and fish. Although the new study is limited by its small size, it could be the first to show odor-based kinship recognition among birds.
New evidence that a sense of smell may be important in birds also makes the study intriguing. For decades, scientists thought that most species of birds responded minimally, if at all, to odor cues. In recent years, though, researchers have uncovered more and more evidence for functionally significant sniffing, such as the odor detection of food out in the open ocean by blue petrels and some other tubenose seabirds.
Odor-based kin recognition would make sense for colony-dwelling birds with lifetime monogamy such as the Humboldt penguins, which return to the same rookeries where they hatched in search of mating prospects. Birds hatched in different years by same parents could easily meet, Mateo says. “If familiarity is the only mechanism available to them, they might say, ‘Hey, I’m not related to you. Let’s have sex.” So a sniff test for kinship could come in handy.
To test the idea, Mateo’s team set up tests of odor discrimination for zoo penguins known to have had significant past contact with each other or not. Oily glandular secretions that the penguins use to preen their feathers provided the odors, and researchers smeared samples onto plastic dog kennels. Birds were allowed a short session of exploring an observation room with a pair of the plastic kennels, each newly perfumed with a different bird’s preen secretion.
Initially, researchers tested the birds’ ability to discriminate scents by comparing kennels scented with a familiar, nonrelated bird with that of an unrelated stranger. The birds spent about six times as long inside the familiar-smelling kennels.
Then researchers added kinship to the mix. In a test of 12 penguins, birds spent more than twice as long inside kennels scented with unfamiliar, unrelated birds than in kennels smelling of unfamiliar kin, the researchers noted.
Also, birds were twice as fast to toddle over and investigate the novel smell of unrelated strangers than when taking a closer sniff of unfamiliar kin. And nine of the 12 penguins entered that unrelated stranger’s kennel first, although neither of these results were as statistically convincing as the time the birds spent inside.
Working with a small colony of 22 birds and no more than 12 penguins for any given test, Mateo acknowledges that some results indicate only trends and more work is needed.
“It’s a very intriguing and promising start,” says avian behavioral ecologist Julie Hagelin of the University of Alaska Fairbanks, who studies chemical communication in birds.
Gabrielle Nevitt of the University of California, Davis, who works on bird olfaction, would like to know more about just what the penguins might have been detecting. “There is currently very little evidence to suggest that volatile signatures associated with preen gland secretion represent necessarily a ‘genetic’ signature of odor,” she says.
Other laboratories are investigating kin recognition by looking at underlying mechanisms, either at the genetic or biochemical level, Nevitt says.