Bug repellent might not set human hearts aflutter, but it does crested auklets. These arctic sea birds produce citrus-scented secretions that repel ticks--and attract mates, according to new research. The discovery clears up a long-standing mystery over the purpose of the compounds, and--because birds rub each other with the secretions during courtship--it represents the first documented transfer of chemical defenses between birds.
Crested auklets (Aethia cristatella) live in massive colonies on islands off Siberia and Alaska. Compounds similar to the auklet secretions act as insecticides in other species, so researchers believed they might play a role as a natural defense against the ticks and other arthropods that plague the birds. In addition, auklets' habit of rubbing the strongly scented napes of each other's necks during courtship fueled speculation that the compounds serve as a sexual attractant. However, the questions have proved difficult to answer, in part because of the remoteness of the birds' habitat.
Hector Douglas found some answers at the zoo. The University of Alaska, Fairbanks, biologist placed two taxidermic auklets into an enclosure with 14 live birds at the home of one of the world's few captive populations--the Cincinnati Zoo. The models were placed on top of rock piles and dispensers placed underneath wafted out the scent of a synthetic version of the auklet "essence."
Auklets approached the scented piles more than twice as often as they did control dispensers containing only ethanol, even rubbing their bills in the scented dispensers, Douglas reported online 17 August in Naturwissenschaften. Douglas also found that wild birds on Alaska's St. Lawrence Island were attracted to the scent, although he used no control in these trials.
To test the odorant's role as an insecticide, Douglas placed ticks near a droplet of the synthetic essence on a petri dish. Although not fatal to the ticks, its scent did slow their pace by more than 50% compared to ethanol controls. Douglas also identified the source of the secretions for the first time, using chemical assays and electron microscopy to pinpoint translucent, hairlike feathers with hollow cores--known as wick feathers--between the birds' shoulder blades.
"These are incredibly exciting conclusions," says Ian Jones, a behavioral ecologist at Memorial University in St. John's, Canada. Jones notes that more work is needed, especially as the ticks used were not the same species that parasitize auklets in the wild and because the study sample was small, but he calls these quibbles.