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Behavior Brief

A round-up of recent discoveries in behavior research

By | September 21, 2011

Dolphin chatter

Dolphin communication seems to be more akin to humans talk than originally thought. Dolphin calls recorded in the 1970s were re-analyzed to reveal that dolphins use tissue vibrations rather than whistles to communicate. The research, published in Biology Letters, broke the recordings down using mathematical computing and visualization scripts. This allowed the team to determine the frequency and harmonics of each whistle-like sound.

The whistles dolphins produce turn out not to be whistles at all, but tissue vibrations akin to the vocalization produced by terrestrial mammals. This explains why dolphins can convey information and identify themselves to one another regardless of the depth they are swimming, the researchers told Wired Science. The findings could have implications for all toothed whales since true whistles would be less effective for communicating the ocean depths. Tissue vibrations allow the animals to recycle air and quickly change their tone mid-chatter, whereas whistling blasts air out at once.

Listen to dolphins talk at Wired Science.

Live hard, age fast 

In many animals, females outlive males. The houbara bustard—a large Middle Eastern bird with elaborate male courtship displays—is no exception to this rule, and it may provide clues about the biological costs of wooing females. Most male houbara bustards age faster than females, Ecology Letters reports, but the most flashy males decline fastest of all.

Researchers used female bustard mannequins to collect sperm samples from enthusiastic males, compiling a ten year record of the birds’ semen outputs, reports Wired Science. These were cross-referenced with each male’s courtship efforts. In their extravagant courting rituals—which involve ornamental shields of long white feathers, running around a rock or bush, and emitting supersonic booming calls, and can continue for up to 18 hours—the most debonair males produce the largest amounts of high quality semen. But this only lasted for a few years: by 4 years of age (captive bustards live up to 20 years), the showiest males’ virility had significantly declined, their ejaculates shrinking in size and containing many dead or abnormal spermatozoa.  Undaunted by their dwindling outputs, however, the birds continued their displays at nearly full-throttle, a desperate ornithological equivalent of human “posers,” the researchers said in a press release.

A male houbara struts his stuff in this video. Credit: Yves Hingrat

Gooey gut hitchhikers 

Horn snails at home in the marsh.
Horn snails at home in the marsh.
KEVIN LAFFERTY

Travel via bird stomach may have been the unlikely method of transportation for two species of marine horn snails that were divided by a land bridge about 3 million years ago. Today, Pacific horn snails occupy the mangroves between Baja to Panama, while the Atlantic horn snails inhabit coasts from Texas to Panama, but at some point since their separation, it appears the two species did come into contact with each other. DNA analysis from 29 populations of snails revealed that the groups had intermingled at least twice, according to a recent study published in Proceedings of the Royal Society: B, about one million years ago and then again about 70,000 years ago.

Researchers suspect that shore birds like herons—in whose bellies the ingested snails can survive for several days—provided airborne transportation over the 200 kilometer stretch dividing the two populations. Such chance events—though extremely rare—have larger ecological implications. Hitchhiking snails can introduce new genes into native populations that could increase resistance to disease, the researchers said in a press release. (Hat tip to ScienceNOW)

Plumage players

 

Fluttering tail feathers create a titillating courtship song
Fluttering tail feathers create a titillating courtship song
ANAND VARMA

When male hummingbirds compete for mates, they climb high into the air on their tiny wings, only to nose-dive back down again at speeds up to 20 meters per second, belting out high-pitched squeaky calls along the way. But the hummers are not humming: research published in Science revealed that it’s the birds’ tail feathers that are actually making the sound.

Ornithologists at Yale University fist identified the fortissimo feathers when they plucked out the hummingbirds’ outermost tail plumes and found this silenced the courting birds. But it still wasn’t clear how the feathers were making the sounds. In the new study, tail feathers from 14 different hummingbird species were put into a wind tunnel that mimicked the birds’ normal dive-bombing velocities. Each groups’ feather made a different sound, and likewise, when the researchers tested the feathers from non-hummingbird genera, they also made individualized, species-specific sounds. Feathery communication could be quite common in the bird world, and may provide a more accurate proxy of a bird’s flight prowess than vocal signals, the researchers said in a press release.

Listen to hummingbird feathers sing. Credit: Christopher Clark

Death-seeking caterpillar zombies

A viral infection will drive this gypsy moth caterpillar to zombie suicide.
A viral infection will drive this gypsy moth caterpillar to zombie suicide.
MICHAEL GROVE

Like something from a horror movie, the baculovirus infects gypsy moths, turning them into automaton zombies that climb to the top of trees to die, liquefy, and rain down viral particles to infect their unsuspecting fellow caterpillars below.  Healthy caterpillars, on the other hand, spend their days hiding in bark crevices and emerge only at night to feed in the safety of darkness.

Though pathogens controlling host behavior is not a new story, the genetic basis for these behavior changes remains a mystery. Researchers now have identified a gene, called egt, which allows the baculovirus to take the joystick and manipulate the caterpillars’ climbing behavior. Researchers placed healthy and infected caterpillars into tall, sealed plastic bottles with food at the bottom. Healthy caterpillars remained below while the infected ones climbed and clung to the top of the container until they died, the researchers describe in Science.  When the scientists deleted the egt gene, this behavior ceased, while reinserting the gene restored the climbing compulsion. This provides the first lead offering a genetic explanation on how some viruses are able to control their host’s behavior, according to the press release.

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