Feathers Aid Bird's Mating Song

Ornithologists have discovered a male bird in South America that attracts mates by rubbing its wings together to generate "songs."

The male club-winged manakin, a colorful, sparrow-size bird that lives on the western slopes of the Andes, evolved special feathers that allow it to produce the unusual calls, the researchers determined.

"Essentially an instrument has evolved in this species, in this case a refined instrument," said Kimberly S. Bostwick of Cornell University, who reported the discovery in the July 29 issue of Science with Richard O. Prum of Yale University. The calls consist of a distinctive "ringing tick-tick-ting" -- described as two "tonal clicks" followed by a "sustained violin-like note."

The researchers found that the birds had special inner feathers -- some with enlarged shafts that form clublike structures that rub against adjacent feathers that have both ridges and enlarged, hollow shafts.

When the researchers examined slow-motion video recordings of the birds, they saw that the creatures produce the "tick" sound by rotating their wings forward and quickly pulling them toward their bodies, which flips the feathers above their backs and causes the tips to rapidly strike together. The birds also "shiver" their wings, causing the feathers to oscillate, creating the "ting."

Although other birds make sounds with their wings, none is as complex as these are, the researchers said. The skill probably evolved because the males are polygamous, making them particularly competitive.

"In general, if an adaptation is really weird and out there, it is produced by sexual selection," Bostwick said in a news release.

-- Rob Stein

More Destructive Hurricanes

Hurricanes have grown stronger and more destructive over the past 30 years, according to a paper published yesterday in the online version of the journal Nature.

The duration of storms and their maximum wind speeds have increased about 50 percent since the mid-1970s, wrote Kerry A. Emanuel, an atmospheric scientist at the Massachusetts Institute of Technology. He charted the increase from records for the North Atlantic and North Pacific oceans.

Despite a rash of hurricanes in the past few years, some scientists say this may not represent a new trend and could be in keeping with past patterns of weather variability. Others, however, have suggested the recent storms could be the result of recent climate change.

Emanuel's study is the first to document that they have become more powerful in recent decades.

"The total energy produced by hurricanes has nearly doubled over the last 30 years, because the intensity has increased by about 50 percent, and they're lasting longer," Emanuel said in an interview.

This increase in storm intensity mirrors the recent rise in ocean surface temperatures, he added, suggesting that global warming may produce fiercer hurricanes.

-- Juliet Eilperin

A Sensitivity to Bitter Tastes

Scientists studying subtle variations in people's taste-bud genes have found evidence that early humans benefited from a random mutation that enhanced their sensitivity to bitter flavors.

Bitterness is one of five tastes that humans can detect. Sensitivity to bitterness can help minimize the odds of getting poisoned, because many natural toxins, including cyanide-based chemicals that plants produce to protect themselves against insects and other predators, are naturally bitter.

A team of researchers from Britain, Germany and the United States looked at variations in a gene that controls bitterness recognition -- variations that make some people more sensitive to bitter tastes than others. An analysis of the global distribution of those gene variants in 997 people from 60 ethnic populations around the world suggested that a version of the gene that makes people extra sensitive to bitterness first arose in Africa as the result of a random mutation about 400,000 years ago.

That version gradually became the dominant form, suggesting it offered people a survival advantage, the team reports in the July 26 issue of Current Biology. At the time the gene arose, they reason, early humans were hunter-gatherers and probably would have benefited from an enhanced ability to avoid toxic plants.

Interestingly, they note, the supersensitive version is less prevalent among people living in parts of Africa where malaria is prevalent. For these people, the scientists speculate, it may make sense to find bitter flavors less aversive, since some cyanide compounds cause red blood cells to deform into a sickle shape that can help resist infection by the malaria parasite.

For these individuals, the team concludes, the small added risk of finding poisonous plants less aversive may be outweighed by those plants' anti-malarial benefits.

-- Rick Weiss

The male club-winged manakin attracts mates by rubbing its wings together to generate "songs." The bird evolved special feathers that allow it to produce the unusual calls, researchers determined.