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The Scent of a Warbler: Birds May Use Sense of Smell in Mating

Study helps puncture myth that scent is a weak sense in avian world



Photo courtesy of Jacques Balthazart

Scientists long believed that birds had little if any sense of smell. That view shifted toward the end of the 20th century, as researchers gradually learned that certain species, such as vultures, kiwis and albatrosses, use olfaction to help find food, and homing pigeons seem to rely at least partly on their nostrils to find their lofts.

New evidence suggests that the sense of smell may play an important role in another vital activity for birds: mating. Researchers report in the journal Behavioural Brain Research) that blocking the nostrils of male Japanese quail before they copulate disrupts the activity of a master gene, called c-Fos, expressed in the brain during sexual reproduction

Study leader Jacques Balthazart, a neuroendocrinologist at the University of Liège in Belgium, says he's not convinced his experiment proves that quail use smell to pick up sex cues from females. "By blocking the nose you interfere with the birds' breathing, which might change brain activity," he says. "But we're seeing these changes in areas that are directly linked to behavior and not respiration."

Balthazart says he would like to conduct a follow-up experiment in which he would sever the quails' olfactory nerves or anesthetize their nasal mucosa and observe the effects on c-Fos activity in the brain during mating.

Whereas sniffer-shy quail still attempted to mate with females, the researchers suspect the males were being driven by sight—birds' primary romantic trigger. Visual cues are so strong in the avian world that male Japanese quail are known to try their luck with stuffed females. Smell deprivation might have more pronounced effects on copulation in sexually naive birds that have not yet developed a strong association between olfactory and visual cues that are typical of females, Balthazart speculates.

Biologist Julie Hagelin of Swarthmore College in Pennsylvania says the latest study has "remarkable promise" to help dispel the stubborn misconception about the role of odors as social signals for birds. Hagelin studies crested auklets, small seabirds that live in cold, northern waters and which produce a tangerine-like odor from their feathers. She believes the citrus scent may serve as a mating signal for auklets, a view bolstered by the fact that the creatures produce the smell almost exclusively during their breeding season.

"The fact that birds like the crested auklet and the Japanese quail are showing these behaviors is really exciting," Hagelin says. "We've potentially hit upon an entirely new mode of communication among birds that has been long overlooked."

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