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Smell May Play Role in Bird Courtship, Study Finds

John Pickrell in England
for National Geographic News
May 27, 2003
 
For centuries ornithologists denied the importance of birds' sense of smell, looking more to birdsong and flashy plumage as typical means of communication. Now, a new study on the striking-looking crested auklet adds to evidence that smell is as important to birds as to other animals.

Scientists report that the sea bird, found in Alaska's Aleutian islands, produces a strong tangerine-like smell which they link to courtship displays. The research, published in an upcoming edition of the journal Proceedings of the Royal Society B, reveals for the first time that birds can be attracted to their own scents, and hints at the use of chemical signals for communication.

Fragranced signals could be a "largely unexplored and possibly widespread means of [bird] communication," says the report.


Unnatural History

19th-century ornithologist and painter John James Audubon might be partly responsibility for spreading the idea that smell was unimportant, said lead researcher Julie Hagelin, a behavioral biologist at Swarthmore College in Pennsylvania.

The results of Audubon's experiment testing whether turkey vultures locate carrion by sight or smell were misinterpreted, she said. The birds flocked upon one deer carcass in the open, but ignored a more decomposed carcass obscured from view. "We now know they use smell to locate food," says Hagelin, "they just prefer fresher carcasses."

The Audubon study began what Hagelin refers to as an "unnatural history" of birds—the assumption that they can't smell.

However, in the last two decades, research has shown both that most birds have a functional sense of smell, and that they use it, like other vertebrates, to gather information. Studies have shown that Corsican blue tits pack nests with fragrant herbs to ward off parasites, and that sea birds locate nesting sites and dinner items by following their noses.

Social odors, chemical signals used to pass messages—such as, "I'm ready to mate" or "get out of my territory!"—to other individuals of the same species, have been found in fish, reptiles, amphibians, and mammals. Their absence in birds seemed surprising, said Hagelin.

However, several unusual attributes of crested auklets, Aethia cristatella, warranted further investigation. Not only did the birds produce a tangerine-like fragrance from the neck-ruff region, but they also exhibited a behavior associated with this region of the body. "A suspicious link between and odor and a display is the best place to start looking for a chemical signal," said Hagelin

Auklet courtship proceeds with cackling vocalizations, and mutual burying of bills in nape and neck feathers, otherwise known as the "ruff-sniff display," said auklet behavior expert Ian Jones, who is with the Atlantic Cooperative Wildlife Ecology Research Network at the Memorial University of Newfoundland, in St. John's, Canada.

Wild Auklet Chase

To test the link, Hagelin joined forces with Jones, and biochemist Bets Rasmussen at the Oregon Graduate Institute in Beaverton. The team collected ruff feathers and carried out behavioral experiments during the breeding months of the Alaskan summer. Feathers collected during winter from captive auklets at the Long Beach Aquarium, California, suggested that the fragrance is only produced during the breeding season.

Chemical analysis of summer feathers revealed fragrance substances, which could be synthesized. The team set up airtight maze experiments on the island breeding colony. A total of 174 temporarily captive wild auklets had a choice of paths that led them to either naturally fragranced auklet plumage, or the unscented plumage of a related species, the parakeet auklet. Other experiments tested their response to synthesized tangerine-like odor chemicals, banana fragrance, and mammalian musk.

The results showed that crested auklets spent up 65 percent of their time in the maze stretches containing scented feathers. They responded even more strongly to more concentrated synthetic auklet odor. The birds were found to avoid musk, and showed no response to banana fragrance, indicating that they could distinguish between fragrances. "Recognizing and distinguishing fragrances is an important [requirement] for chemical communication," said Hagelin.

The fragrance might act as a "sexual ornament," said Hagelin. Crested auklets already display other traits such as bright beaks, which are used, like the peacocks' tail, to attract mates or advertise status. The strength of a bird's smell might signal its quality to a mate, though this requires further investigation, said Hagelin.

Instant Messenger

It's too early to establish how important social odors are in other species, but the potential for scent signals certainly exists. Many birds produce odors detectable to people, and mutually preen plumage, which could transmit information.

A related species, the whiskered auklet, has a similar tangerine-like plumage odor, and other sea birds such as shearwaters and storm petrels have distinct musky odors. The kakapo, an endangered, flightless parrot from New Zealand, has a sweet musky scent detectable meters away.

"This is a great study," said Bart Kempenaers, ornithologist at the Max Planck Research Centre for Ornithology in Seewiesen, Germany. "There have been few studies on the importance of smell in birds." The next step is to establish if the fragrance has any role in how crested auklets choose their mates, he said.

For many years researchers ignored the importance of smell in birds, said Kempenaers, but new studies are slowly challenging that view. "I guess it all boils down to our prejudices," biased by how we ourselves view the world, he said.

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